Combined QP-specific pre-trained filters

Abstract

Multiple Quantization Parameter (QP)-specific pre-trained filters may be combined during Adaptive Loop Filtering (ALF). A video coding device, which may be, for example, an encoder device or a decoder device, may comprise at least one processor configured to determine a plurality of pre-trained ALF QP-specific filter sets. The video coding device may determine a QP value and may select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets from the plurality of pre-trained ALF QP-specific filters sets. The video coding device may apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples. The video coding device may combine the respective output samples.

Description

COMBINED QP-SPECIFIC PRE-TRAINED FILTERSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of EP patent application number 24305050.7 filed January 9, 2024, the contents of which are hereby incorporated by reference herein in their entirety.BACKGROUND

[0002] Video coding systems may be used to compress digital video signals, e.g., to reduce the storage and / or transmission bandwidth needed for such signals. Video coding systems may include, for example, block-based, wavelet-based, and / or object-based systems.SUMMARY

[0003] Systems, methods, and instrumentalities are disclosed for combining multiple Quantization Parameter (QP)-specific pre-trained filters during Adaptive Loop Filtering (ALF).

[0004] A video encoding device, which may be referred to as an encoder, may comprise at least one processor and may be configured to determine a quantization parameter (QP) value and to select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets. The video encoding device may be configured to apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples, and to combine the respective output samples.

[0005] The plurality of ALF QP-specific filter sets may comprise two ALF QP-specific filter sets. The video encoding device may be further configured to determine, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor. The video encoding device configured to combine the respective output samples may be further configured to apply a respective weighting factor to a corresponding one of the respective output samples. The video encoding device may be further configured to send, for each CTU comprised in the video data, the respective weighting factor.

[0006] The video encoding device may be configured to derive, based on the QP value, a first weighting factor and a second weighting factor. The video encoding device configured to combine the respective output samples may be configured to apply the first weighting factor to a first of the respective output samples and to apply the second weighting factor to a second of the respective output samples.

[0007] The video encoding device may be configured to determine an adaptive filter with at least one added tap. The video encoding device configured to combine the respective output samples may be configured to apply the adaptive filter with at least one added tap. The video encoding device may be further configured to send an indication of the adaptive filter with at least one added tap.

[0008] A video decoding device, which may be referred to as a decoder, may comprise at least one processor and may be configured to determine a quantization parameter (QP) value, and to select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets. The video decoding device may be configured to apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples, and to combine the respective output samples.

[0009] The plurality of ALF QP-specific filter sets may comprise two ALF QP-specific filter sets. The video decoding device may be further configured to determine, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor. The video decoding device configured to combine the respective output samples may be further configured to apply a respective weighting factor to a corresponding one of the respective output samples. The respective weighting factors may be received in the video data.

[0010] The video decoding device may be configured to determine an adaptive filter with at least one added tap. The video decoding device may receive an indication of the adaptive filter with at least one added tap. The video decoding device configured to combine the respective output samples may be configured to apply the adaptive filter with at least one added tap.

[0011] A video coding device, which may be, for example, an encoder device or a decoder device, may comprise at least one processor configured to determine a plurality of pre-trained ALF QP-specific filter sets. The video coding device may determine a QP value and may select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets from the plurality of pre-trained ALF QP- specific filters sets. The video coding device may apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples. The video coding device may combine the respective output samples.

[0012] The video coding device may determine that the plurality of ALF QP-specific filter sets comprise two ALF QP-specific filter sets. The video coding device may determine, for each CTU comprised in the video data, a respective weighting factor. The video coding device may send the video data and, for each CTU comprised in the video data, may send the respective weighting factor. The video coding device may be further configured to send in the video data an indication the plurality of ALF QP-specific filter sets have been applied.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented.

[0014] FIG. 1 B is a system diagram illustrating an example wireless transmit / receive unit (WTRU) thatmay be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0015] FIG. 1 C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0016] FIG. 1 D is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0017] FIG. 2 illustrates an example video encoder.

[0018] FIG. 3 illustrates an example video decoder.

[0019] FIG. 4 illustrates an example of a system in which various aspects and examples may be implemented.

[0020] FIG. 5 illustrates a workflow of example loop filtering.

[0021] FIG. 6 illustrates an example implementation of ALF filters.

[0022] FIG. 7 depicts a workflow of example filtering.

[0023] FIG. 8 illustrates example minimum and maximum filter set indices.

[0024] FIG. 9 illustrates an example luma ALF signaled filter shape.

[0025] FIG. 10 illustrates an example process for combining QP-eligi ble filters.

[0026] FIG. 11 illustrates an example 37-tap signaled adaptive filter shape.

[0027] FIG. 12 illustrates an example 40-tap signaled adaptive filter shape.DETAILED DESCRIPTION

[0028] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings.

[0029] FIG. 1A is a diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0030] As shown in FIG. 1A, the communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a RAN 104 / 113, a CN 106 / 115, a public switched telephonenetwork (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a “station” and / or a “STA”, may be configured to transmit and / or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c and 102d may be interchangeably referred to as a UE.

[0031] The communications systems 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106 / 115, the Internet 110, and / or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a gNB, a NR NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0032] The base station 114a may be part of the RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector ofthe cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0033] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0034] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 115 / 116 / 117 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and / or High-Speed UL Packet Access (HSUPA).

[0035] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A) and / or LTE-Advanced Pro (LTE-A Pro).

[0036] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access, which may establish the air interface 116 using New Radio (NR).

[0037] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for instance using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to / from multiple types of base stations (e.g., an eNB and a gNB).

[0038] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0039] The base station 114b in FIG. 1 A may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106 / 115.

[0040] The RAN 104 / 113 may be in communication with the CN 106 / 115, which may be any type of network configured to provide voice, data, applications, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 / 115 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 / 113 and / or the CN 106 / 115 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 / 113 or a different RAT. For example, in addition to being connected to the RAN 104 / 113, which may be utilizing a NR radio technology, the CN 106 / 115 may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0041] The CN 106 / 115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or the other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and / or the internet protocol (IP) in the TCP / IP internet protocol suite. The networks 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 / 113 or a different RAT.

[0042] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0043] FIG. 1 B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1 B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138, among others. It will be appreciated that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0044] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1 B depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0045] The transmit / receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0046] Although the transmit / receive element 122 is depicted in FIG. 1 B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or moretransmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0047] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit / receive element 122 and to demodulate the signals that are received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11 , for example.

[0048] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 and / or the removable memory 132. The nonremovable memory 130 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0049] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0050] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0051] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs and / or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a Virtual Reality and / or Augmented Reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor; an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and / or a humidity sensor.

[0052] The WTRU 102 may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and downlink (e.g., for reception) may be concurrent and / or simultaneous. The full duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor 118). In an embodiment, the WRTU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the downlink (e.g., for reception)).

[0053] FIG. 1 C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0054] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a.

[0055] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, and the like. As shown in FIG. 1 C, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0056] The CN 106 shown in FIG. 1 C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. While each of the foregoing elements are depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0057] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0058] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0059] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0060] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers.

[0061] Although the WTRU is described in FIGS. 1 A-1 D as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network.

[0062] In representative embodiments, the other network 112 may be a WLAN.

[0063] A WLAN in Infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have an access or an interface to a Distribution System (DS) or another type of wired / wireless network that carries traffic in to and / or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be consideredand / or referred to as peer-to-peer traffic. The peer-to-peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11e DLS or an 802.11 z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an “ad-hoc” mode of communication.

[0064] When using the 802.11 ac infrastructure mode of operation or a similar mode of operations, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented, for example, in 802.11 systems. For CSMA / CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0065] High Throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHz wide channel.

[0066] Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. The 40 MHz, and / or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse Fast Fourier Transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above-described operation for the 80+80 configuration may be reversed, and the combined data may be sent to the Medium Access Control (MAC).

[0067] Sub 1 GHz modes of operation are supported by 802.11af and 802.11 ah. The channel operating bandwidths, and carriers, are reduced in 802.11af and 802.11 ah relative to those used in 802.11 n, and 802.11ac. 802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11 ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11 ah may support Meter Type Control / Machine-Type Communications, such as MTC devices in a macro coverage area. MTCdevices may have certain capabilities, for example, limited capabilities including support for (e.g., only support for) certain and / or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life).

[0068] WLAN systems, which may support multiple channels, and channel bandwidths, such as 802.11 n, 802.11 ac, 802.11 af, and 802.11 ah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA, from among all STAs operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.11 ah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or Network Allocation Vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode), transmitting to the AP, the entire available frequency bands may be considered busy even though a majority of the frequency bands remains idle and may be available.

[0069] In the United States, the available frequency bands, which may be used by 802.11 ah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the available frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11 ah is 6 MHz to 26 MHz depending on the country code.

[0070] FIG. 1 D is a system diagram illustrating the RAN 113 and the CN 115 according to an embodiment. As noted above, the RAN 113 may employ an NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also be in communication with the CN 115.

[0071] The RAN 113 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point(CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0072] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing varying number of OFDM symbols and / or lasting varying lengths of absolute time).

[0073] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing other RANs (e.g., such as eNode-Bs 160a, 160b, 160c). In the standalone configuration, WTRUs 102a, 102b, 102c may utilize one or more gNBs 180a, 180b, 180c as a mobility anchor point. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration WTRUs 102a, 102b, 102c may communicate with / connect to gNBs 180a, 180b, 180c while also communicating with / connecting to another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In the non-standalone configuration, eNode- Bs 160a, 160b, 160c may serve as a mobility anchor for WTRUs 102a, 102b, 102c and gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for servicing WTRUs 102a, 102b, 102c.

[0074] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support of network slicing, dual connectivity, interworking between NR and E- UTRA, routing of user plane data towards User Plane Function (UPF) 184a, 184b, routing of control plane information towards Access and Mobility Management Function (AMF) 182a, 182b and the like. As shown in FIG. 1 D, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface.

[0075] The CN 115 shown in FIG. 1 D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. While each of the foregoing elements are depicted as part of the CN 115, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0076] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N2 interface and may serve as a control node. For example, the AMF 182a, 182b maybe responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different PDU sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of NAS signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b in order to customize CN support for WTRUs 102a, 102b, 102c based on the types of services being utilized WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases such as services relying on ultrareliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for machine type communication (MTC) access, and / or the like. The AMF 162 may provide a control plane function for switching between the RAN 113 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi.

[0077] The SMF 183a, 183b may be connected to an AMF 182a, 182b in the CN 115 via an N11 interface. The SMF 183a, 183b may also be connected to a UPF 184a, 184b in the CN 115 via an N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP address, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, and the like. A PDU session type may be IP-based, non-IP based, Ethernet-based, and the like.

[0078] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like.

[0079] The CN 115 may facilitate communications with other networks. For example, the CN 115 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 115 and the PSTN 108. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to a local Data Network (DN) 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and an N6 interface between the UPF 184a, 184b and the DN 185a, 185b.

[0080] In view of Figures 1 A-1 D, and the corresponding description of Figures 1 A-1 D, one or more, or all, of the functions described herein with regard to one or more of: WTRU 102a-d, Base Station 114a-b,eNode-B 160a-c, MME 162, SGW 164, PGW 166, gNB 180a-c, AMF 182a-b, UPF 184a-b, SMF 183a-b, DN 185a-b, and / or any other device(s) described herein, may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0081] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and / or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and / or may perform testing using over-the-air wireless communications.

[0082] The one or more emulation devices may perform the one or more, including all, functions while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and / or a nondeployed (e.g., testing) wired and / or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0083] This application describes a variety of aspects, including tools, features, examples, models, approaches, etc. Many of these aspects are described with specificity and, at least to show the individual characteristics, are often described in a manner that may sound limiting. However, this is for purposes of clarity in description, and does not limit the application or scope of those aspects. Indeed, all of the different aspects may be combined and interchanged to provide further aspects. Moreover, the aspects may be combined and interchanged with aspects described in earlier filings as well.

[0084] The aspects described and contemplated in this application may be implemented in many different forms. FIGS. 5-12 described herein may provide some examples, but other examples are contemplated. The discussion of FIGS. 5-12 does not limit the breadth of the implementations. At least one of the aspects generally relates to video encoding and decoding, and at least one other aspect generally relates to transmitting a bitstream generated or encoded. These and other aspects may be implemented as a method, an apparatus, a computer readable storage medium having stored thereon instructions for encoding or decoding video data according to any of the methods described, and / or acomputer readable storage medium having stored thereon a bitstream generated according to any of the methods described.

[0085] In the present application, the terms “reconstructed” and “decoded” may be used interchangeably, the terms “pixel” and “sample” may be used interchangeably, the terms “image,” “picture” and “frame” may be used interchangeably.

[0086] Various methods are described herein, and each of the methods comprises one or more steps or actions for achieving the described method. Unless a specific order of steps or actions is required for proper operation of the method, the order and / or use of specific steps and / or actions may be modified or combined. Additionally, terms such as “first”, “second”, etc. may be used in various examples to modify an element, component, step, operation, etc., such as, for example, a “first decoding” and a “second decoding”. Use of such terms does not imply an ordering to the modified operations unless specifically required. So, in this example, the first decoding need not be performed before the second decoding, and may occur, for example, before, during, or in an overlapping time period with the second decoding.

[0087] Various methods and other aspects described in this application may be used to modify modules, for example, decoding modules, of a video encoder 200 and decoder 300 as shown in FIG. 2 and FIG. 3. Moreover, the subject matter disclosed herein may be applied, for example, to any type, format or version of video coding, whether described in a standard or a recommendation, whether preexisting or future-developed, and extensions of any such standards and recommendations. Unless indicated otherwise, or technically precluded, the aspects described in this application may be used individually or in combination.

[0088] Various numeric values are used in examples described in the present application, such as filtered values, clipping parameters, etc. These and other specific values are for the purpose of describing examples and the aspects described are not limited to these specific values.

[0089] FIG. 2 is a diagram showing an example video encoder. Variations of example encoder 200 are contemplated, but the encoder 200 is described below for purposes of clarity without describing all expected variations.

[0090] Before being encoded, the video sequence may go through pre-encoding processing (201 ), for example, applying a color transform to the input color picture (e.g., conversion from RGB 4:4:4 to YCbCr 4:2:0), or performing a remapping of the input picture components in order to get a signal distribution more resilient to compression (for instance using a histogram equalization of one of the color components). Metadata may be associated with the pre-processing and attached to the bitstream.

[0091] In the encoder 200, a picture is encoded by the encoder elements as described below. The picture to be encoded is partitioned (202) and processed in units of, for example, coding units (CUs). Each unit is encoded using, for example, either an intra or inter mode. When a unit is encoded in an intramode, it performs intra prediction (260). In an inter mode, motion estimation (275) and compensation (270) are performed. The encoder decides (205) which one of the intra mode or inter mode to use for encoding the unit, and indicates the intra / inter decision by, for example, a prediction mode flag. Prediction residuals are calculated, for example, by subtracting (210) the predicted block from the original image block.

[0092] The prediction residuals are then transformed (225) and quantized (230). The quantized transform coefficients, as well as motion vectors and other syntax elements, are entropy coded (245) to output a bitstream. The encoder can skip the transform and apply quantization directly to the nontransformed residual signal. The encoder can bypass both transform and quantization, i.e. , the residual is coded directly without the application of the transform or quantization processes.

[0093] The encoder decodes an encoded block to provide a reference for further predictions. The quantized transform coefficients are de-quantized (240), and inverse transformed (250) to decode prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. In-loop filters (265) are applied to the reconstructed picture to perform, for example, deblocking / SAO (Sample Adaptive Offset) / ALF (Adaptive Loop Filter) filtering to reduce encoding artifacts. The filtered image is stored at a reference picture buffer (280).

[0094] FIG. 3 is a diagram showing an example of a video decoder. In example decoder 300, a bitstream is decoded by the decoder elements as described below. Video decoder 300 generally performs a decoding pass reciprocal to the encoding pass as described in FIG. 2. The encoder 200 also generally performs video decoding as part of encoding video data.

[0095] In particular, the input of the decoder includes a video bitstream, which may be generated by video encoder 200. The bitstream is first entropy decoded (330) to obtain transform coefficients, motion vectors, and other coded information. The picture partition information indicates how the picture is partitioned. The decoder may therefore divide (335) the picture according to the decoded picture partitioning information. The transform coefficients are de-quantized (340) and inverse transformed (350) to decode the prediction residuals. Combining (355) the decoded prediction residuals and the predicted block, an image block is reconstructed. The predicted block may be obtained (370) from intra prediction (360) or motion-compensated prediction (i.e., inter prediction) (375). In-loop filters (365) are applied to the reconstructed image. The filtered image is stored at a reference picture buffer (380). Note that, for a given picture, the contents of the reference picture buffer 380 on the decoder 300 side is identical to the contents of the reference picture buffer 280 on the encoder 200 side for the same picture.

[0096] The decoded picture can further go through post-decoding processing (385), for example, an inverse color transform (e.g., conversion from YCbCr 4:2:0 to RGB 4:4:4) or an inverse remapping performing the inverse of the remapping process performed in the pre-encoding processing (201). Thepost-decoding processing can use metadata derived in the pre-encoding processing and signaled in the bitstream. In an example, the decoded images (e.g., after application of the in-loop filters (365) and / or after post-decoding processing (385), if post-decoding processing is used) may be sent to a display device for rendering to a user.

[0097] FIG. 4 is a diagram showing an example of a system in which various aspects and examples described herein may be implemented. System 400 may be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this document. Examples of such devices include, but are not limited to, various electronic devices such as personal computers, laptop computers, smartphones, tablet computers, digital multimedia set top boxes, digital television receivers, personal video recording systems, connected home appliances, and servers. Elements of system 400, singly or in combination, may be embodied in a single integrated circuit (IC), multiple ICs, and / or discrete components. For example, in at least one example, the processing and encoder / decoder elements of system 400 are distributed across multiple ICs and / or discrete components. In various examples, the system 400 is communicatively coupled to one or more other systems, or other electronic devices, via, for example, a communications bus or through dedicated input and / or output ports. In various examples, the system 400 is configured to implement one or more of the aspects described in this document.

[0098] The system 400 includes at least one processor 410 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this document. Processor 410 can include embedded memory, input output interface, and various other circuitries as known in the art. The system 400 includes at least one memory 420 (e.g., a volatile memory device, and / or a non-volatile memory device). System 400 includes a storage device 440, which can include non-volatile memory and / or volatile memory, including, but not limited to, Electrically Erasable Programmable Read-Only Memory (EEPROM), Read-Only Memory (ROM), Programmable Read-Only Memory (PROM), Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), flash, magnetic disk drive, and / or optical disk drive. The storage device 440 can include an internal storage device, an attached storage device (including detachable and non-detachable storage devices), and / or a network accessible storage device, as non-limiting examples.

[0099] System 400 includes an encoder / decoder module 430 configured, for example, to process data to provide an encoded video or decoded video, and the encoder / decoder module 430 can include its own processor and memory. The encoder / decoder module 430 represents module(s) that may be included in a device to perform the encoding and / or decoding functions. As is known, a device can include one or both of the encoding and decoding modules. Additionally, encoder / decoder module 430 may beimplemented as a separate element of system 400 or may be incorporated within processor 410 as a combination of hardware and software as known to those skilled in the art.

[0100] Program code to be loaded onto processor 410 or encoder / decoder 430 to perform the various aspects described in this document may be stored in storage device 440 and subsequently loaded onto memory 420 for execution by processor 410. In accordance with various examples, one or more of processor 410, memory 420, storage device 440, and encoder / decoder module 430 can store one or more of various items during the performance of the processes described in this document. Such stored items can include, but are not limited to, the input video, the decoded video or portions of the decoded video, the bitstream, matrices, variables, and intermediate or final results from the processing of equations, formulas, operations, and operational logic.

[0101] In some examples, memory inside of the processor 410 and / or the encoder / decoder module 430 is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. In other examples, however, a memory external to the processing device (for example, the processing device may be either the processor 410 or the encoder / decoder module 430) is used for one or more of these functions. The external memory may be the memory 420 and / or the storage device 440, for example, a dynamic volatile memory and / or a non-volatile flash memory. In several examples, an external non-volatile flash memory is used to store the operating system of, for example, a television. In at least one example, a fast external dynamic volatile memory such as a RAM is used as working memory for video encoding and decoding operations.

[0102] The input to the elements of system 400 may be provided through various input devices as indicated in block 445. Such input devices include, but are not limited to, (i) a radio frequency (RF) portion that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a Component (COMP) input terminal (or a set of COMP input terminals), (iii) a Universal Serial Bus (USB) input terminal, and / or (iv) a High-Definition Multimedia Interface (HDMI) input terminal. Other examples, not shown in FIG. 4, include composite video.

[0103] In various examples, the input devices of block 445 have associated respective input processing elements as known in the art. For example, the RF portion may be associated with elements suitable for (i) selecting a desired frequency (also referred to as selecting a signal, or band-limiting a signal to a band of frequencies), (ii) down converting the selected signal, (iii) band-limiting again to a narrower band of frequencies to select (for example) a signal frequency band which may be referred to as a channel in certain examples, (iv) demodulating the down converted and band-limited signal, (v) performing error correction, and / or (vi) demultiplexing to select the desired stream of data packets. The RF portion of various examples includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters,demodulators, error correctors, and demultiplexers. The RF portion can include a tuner that performs various of these functions, including, for example, down converting the received signal to a lower frequency (for example, an intermediate frequency or a near-baseband frequency) or to baseband. In one set-top box example, the RF portion and its associated input processing element receives an RF signal transmitted over a wired (for example, cable) medium, and performs frequency selection by filtering, down converting, and filtering again to a desired frequency band. Various examples rearrange the order of the above-described (and other) elements, remove some of these elements, and / or add other elements performing similar or different functions. Adding elements can include inserting elements in between existing elements, such as, for example, inserting amplifiers and an analog-to-digital converter. In various examples, the RF portion includes an antenna.

[0104] The USB and / or HDMI terminals can include respective interface processors for connecting system 400 to other electronic devices across USB and / or HDMI connections. It is to be understood that various aspects of input processing, for example, Reed-Solomon error correction, may be implemented, for example, within a separate input processing IC or within processor 410 as necessary. Similarly, aspects of USB or HDMI interface processing may be implemented within separate interface ICs or within processor 410 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 410, and encoder / decoder 430 operating in combination with the memory and storage elements to process the data stream as necessary for presentation on an output device.

[0105] Various elements of system 400 may be provided within an integrated housing, Within the integrated housing, the various elements may be interconnected and transmit data therebetween using suitable connection arrangement 425, for example, an internal bus as known in the art, including the I nter-IC (I2C) bus, wiring, and printed circuit boards.

[0106] The 400 system includes communication interface 450 that enables communication with other devices via communication channel 460. The communication interface 450 can include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 460. The communication interface 450 can include, but is not limited to, a modem or network card and the communication channel 460 may be implemented, for example, within a wired and / or a wireless medium.

[0107] Data is streamed, or otherwise provided, to the system 400, in various examples, using a wireless network such as a Wi-Fi network, for example IEEE 802.11 (IEEE refers to the Institute of Electrical and Electronics Engineers). The Wi-Fi signal of these examples is received over the communications channel 460 and the communications interface 450 which are adapted for Wi-Fi communications. The communications channel 460 of these examples is typically connected to an access point or router that provides access to external networks including the Internet for allowingstreaming applications and other over-the-top communications. Other examples provide streamed data to the system 400 using a set-top box that delivers the data over the HDMI connection of the input block 445. Still other examples provide streamed data to the system 400 using the RF connection of the input block 445. As indicated above, various examples provide data in a non-streaming manner. Additionally, various examples use wireless networks other than Wi-Fi, for example a cellular network or a Bluetooth® network.

[0108] The system 400 can provide an output signal to various output devices, including a display 475, speakers 485, and other peripheral devices 495. The display 475 of various examples includes one or more of, for example, a touchscreen display, an organic light-emitting diode (OLED) display, a curved display, and / or a foldable display. The display 475 may be for a television, a tablet, a laptop, a cell phone (mobile phone), or other device. The display 475 can also be integrated with other components (for example, as in a smart phone), or separate (for example, an external monitor for a laptop). The other peripheral devices 495 include, in various examples, one or more of a stand-alone digital video disc (or digital versatile disc) (DVD, for both terms), a disk player, a stereo system, and / or a lighting system. Various examples use one or more peripheral devices 495 that provide a function based on the output of the system 400. For example, a disk player performs the function of playing the output of the system 400.

[0109] In various examples, control signals are communicated between the system 400 and the display 475, speakers 485, or other peripheral devices 495 using signaling such as AV. Link, Consumer Electronics Control (CEC), or other communications protocols that enable device-to-device control with or without user intervention. The output devices may be communicatively coupled to system 400 via dedicated connections through respective interfaces 470, 480, and 490. Alternatively, the output devices may be connected to system 400 using the communications channel 460 via the communications interface 450. The display 475 and speakers 485 may be integrated in a single unit with the other components of system 400 in an electronic device such as, for example, a television. In various examples, the display interface 470 includes a display driver, such as, for example, a timing controller (T Con) chip.

[0110] The display 475 and speakers 485 can alternatively be separated from one or more of the other components, for example, if the RF portion of input 445 is part of a separate set-top box. In various examples in which the display 475 and speakers 485 are external components, the output signal may be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs.

[0111] The examples may be carried out by computer software implemented by the processor 410 or by hardware, or by a combination of hardware and software. As a non-limiting example, the examplesmay be implemented by one or more integrated circuits. The memory 420 may be of any type appropriate to the technical environment and may be implemented using any appropriate data storage technology, such as optical memory devices, magnetic memory devices, semiconductor-based memory devices, fixed memory, and removable memory, as non-limiting examples. The processor 410 may be of any type appropriate to the technical environment, and can encompass one or more of microprocessors, general purpose computers, special purpose computers, and processors based on a multi-core architecture, as non-limiting examples.

[0112] Various implementations involve decoding. “Decoding”, as used in this application, can encompass all or part of the processes performed, for example, on a received encoded sequence in order to produce a final output suitable for display. In various examples, such processes include one or more of the processes typically performed by a decoder, for example, entropy decoding, inverse quantization, inverse transformation, and differential decoding. In various examples, such processes also, or alternatively, include processes performed by a decoder of various implementations described in this application, for example, attendant to combining multiple QP-specific filtering processes, etc.

[0113] As further examples, in one example “decoding” refers only to entropy decoding, in another example “decoding” refers only to differential decoding, and in another example “decoding” refers to a combination of entropy decoding and differential decoding. Whether the phrase “decoding process” is intended to refer specifically to a subset of operations or generally to the broader decoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art.

[0114] Various implementations involve encoding. In an analogous way to the above discussion about “decoding”, “encoding” as used in this application can encompass all or part of the processes performed, for example, on an input video sequence in order to produce an encoded bitstream. In various examples, such processes include one or more of the processes typically performed by an encoder, for example, partitioning, differential encoding, transformation, quantization, and entropy encoding. In various examples, such processes also, or alternatively, include processes performed by an encoder of various implementations described in this application, for example, to combine multiple QP-specific filtering processes, etc.

[0115] As further examples, in one example “encoding” refers only to entropy encoding, in another example “encoding” refers only to differential encoding, and in another example “encoding” refers to a combination of differential encoding and entropy encoding. Whether the phrase “encoding process” is intended to refer specifically to a subset of operations or generally to the broader encoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art.

[0116] Note that syntax elements as used herein are descriptive terms. As such, they do not preclude the use of other syntax element names.

[0117] When a figure is presented as a flow diagram, it should be understood that it also provides a block diagram of a corresponding apparatus. Similarly, when a figure is presented as a block diagram, it should be understood that it also provides a flow diagram of a corresponding method / process.

[0118] The implementations and aspects described herein may be implemented in, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method), the implementation of features discussed can also be implemented in other forms (for example, an apparatus or program). An apparatus may be implemented in, for example, appropriate hardware, software, and firmware. The methods may be implemented in, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. Processors also include communication devices, such as, for example, computers, cell phones, portable / personal digital assistants ("PDAs"), and other devices that facilitate communication of information between end-users.

[0119] Reference to “one example” or “an example” or “one implementation” or “an implementation”, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the example is included in at least one example. Thus, the appearances of the phrase “in one example” or “in an example” or “in one implementation” or “in an implementation”, as well any other variations, appearing in various places throughout this application are not necessarily all referring to the same example.

[0120] Additionally, this application may refer to “determining” various pieces of information. Determining the information can include one or more of, for example, estimating the information, calculating the information, predicting the information, or retrieving the information from memory. Obtaining may include receiving, retrieving, constructing, generating, and / or determining.

[0121] Further, this application may refer to “accessing” various pieces of information. Accessing the information can include one or more of, for example, receiving the information, retrieving the information (for example, from memory), storing the information, moving the information, copying the information, calculating the information, determining the information, predicting the information, or estimating the information.

[0122] Additionally, this application may refer to “receiving” various pieces of information. Receiving is, as with “accessing”, intended to be a broad term. Receiving the information can include one or more of, for example, accessing the information, or retrieving the information (for example, from memory). Further, “receiving” is typically involved, in one way or another, during operations such as, for example,storing the information, processing the information, transmitting the information, moving the information, copying the information, erasing the information, calculating the information, determining the information, predicting the information, or estimating the information.

[0123] It is to be appreciated that the use of any of the following 7”, “and / or”, and “at least one of’, for example, in the cases of “A / B”, “A and / or B” and “at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and / or C” and “at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This may be extended, as is clear to one of ordinary skill in this and related arts, for as many items as are listed.

[0124] Also, as used herein, the word “signal” refers to, among other things, indicating something to a corresponding decoder. Encoder signals may include, for example, any attendant to combining multiple QP-specific filters. In this way, in an example the same parameter is used at both the encoder side and the decoder side. Thus, for example, an encoder can transmit (explicit signaling) a particular parameter to the decoder so that the decoder can use the same particular parameter. Conversely, if the decoder already has the particular parameter as well as others, then signaling may be used without transmitting (implicit signaling) to simply allow the decoder to know and select the particular parameter. By avoiding transmission of any actual functions, a bit savings is realized in various examples. It is to be appreciated that signaling may be accomplished in a variety of ways. For example, one or more syntax elements, flags, and so forth are used to signal information to a corresponding decoder in various examples. While the preceding relates to the verb form of the word “signal”, the word “signal” can also be used herein as a noun.

[0125] As will be evident to one of ordinary skill in the art, implementations may produce a variety of signals formatted to carry information that may be, for example, stored or transmitted. The information can include, for example, instructions for performing a method, or data produced by one of the described implementations. For example, a signal may be formatted to carry the bitstream of a described example. Such a signal may be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information that the signal carries may be, for example, analog or digital information. The signal may be transmitted over avariety of different wired or wireless links, as is known. The signal may be stored on, or accessed or received from, a processor-readable medium.

[0126] Many examples are described herein. Features of examples may be provided alone or in any combination, across various claim categories and types. Further, examples may include one or more of the features, devices, or aspects described herein, alone or in any combination, across various claim categories and types. For example, features described herein may be implemented in a bitstream or signal that includes information generated as described herein. The information may allow a decoder to decode a bitstream, the encoder, bitstream, and / or decoder according to any of the embodiments described. For example, features described herein may be implemented by creating and / or transmitting and / or receiving and / or decoding a bitstream or signal. For example, features described herein may be implemented a method, process, apparatus, medium storing instructions, medium storing data, or signal. For example, features described herein may be implemented by a TV, set-top box, cell phone, tablet, or other electronic device that performs decoding. The TV, set-top box, cell phone, tablet, or other electronic device may display (e.g., using a monitor, screen, or other type of display) a resulting image (e.g., an image from residual reconstruction of the video bitstream). The TV, set-top box, cell phone, tablet, or other electronic device may receive a signal including an encoded image and perform decoding.

[0127] Systems, methods, and instrumentalities are disclosed for combining multiple Quantization Parameter (QP)-specific pre-trained filters during Adaptive Loop Filtering (ALF). A video coding device, which may be, for example, an encoder device or a decoder device, may comprise at least one processor configured to determine a plurality of pre-trained ALF QP-specific filter sets. The video coding device may determine a QP value and may select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets from the plurality of pre-trained ALF QP-specific filters sets. The video coding device may apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples. The video coding device may combine the respective output samples.

[0128] In-loop filters may be provided. Block-based intra / inter prediction and transform coding, together with residuals quantization, may induce a variety of artifacts at medium and low bitrates. To reduce those artifacts, in-loop filters, such as Deblocking Filtering (DBF), Bilateral Filtering (BIF), Sample- Adaptive Offset (SAO), and Adaptive Loop Filtering (ALF) may be used.

[0129] Deblocking Filter (DBF) may aim at smoothing discontinuities that may appear along block boundaries. Sample-Adaptive Offset (SAO) may be designed to attenuate artifacts occurring around edges and correct the local average intensity changes (e.g., banding artifact) with offsets signaled in the bitstream. Bilateral Filter (BIF) may aim at denoising further reconstructed pictures from artifacts inducedfrom quantization in the transform domain. Adaptive Loop Filters (ALF) may be determined at the encoder side as optimal filters according to a rate-distortion criterion. ALF filters may be transmitted along with the bitstream and may be subsequently retrieved and used at the decoder side.

[0130] In-loop filters may be provided. Example in-loop filters may include a Deblocking Filter (DBF); a Sample-Adaptive Offset (SAO); and an Adaptive Loop Filter (ALF). The Deblocking Filter may aim at reducing blocking discontinuities. The Sample-Adaptive Offset may aim, e.g., may mostly aim, at reducing artifacts resulting from the quantization of transform coefficients. An Adaptive Loop Filter and Cross-Component Adaptive Loop Filter may be adaptive filters enabled to enhance the reconstructed signal, using, for example, Wiener-filter encoding approaches.

[0131] A workflow depicting example loop filtering is depicted in FIG. 5. If local deblocking conditions are met, Luma and Chroma reconstructed samples located along block boundaries may be first filtered with Deblocking Filters (DBF). Offsets may be added locally depending on a classification based on bandclassifier or edge-classifier with Sample-Adaptive Offset (SAO). Adaptive-Loop Filters (ALF) may be performed before storing the resulting sample values in the Reference Picture buffer.

[0132] An Adaptive Loop Filter (ALF) may be provided. An ALF may be an adaptive filter that may be applied to reduce the mean square error (MSE) between the original and the reconstructed samples, and may use, for example, Wiener-filter encoding approaches.

[0133] ALF filters may be transmitted in the bitstream and decoded at the decoder side before being applied on reconstructed samples. Pre-trained ALF filters may also be hard-coded both at the encoder and decoder sides.

[0134] ALF may be point-symmetrical and DC-neutral with integer coefficients. FIG. 6 depicts an example implementation of ALF filters. As shown on the left of FIG. 6, ALF may use 7x7 diamond-shaped filters for Luma. As shown on the right of FIG. 6, ALF may use 5x5 diamond-shaped filters for Chroma.

[0135] Filtering operations may be provided. Let R (x, y) be a reconstructed sample and let R(x, y) denote its ALF-filtered value. In the linear implementation of ALF, R(x, y) may be computed as:where ( )0<i<N-i denote the filter coefficients, and:AR+ = R (x + xt, y + yd - R (x, y)AR = R(x - xt, y - yd ~ R(x, y)with (±xf, ±y£) denoting the coordinates offset corresponding to the reconstructed samples associated with the i-th coefficient ct.

[0136] In the non-linear implementation of ALF, Equation (1) becomes:with:where btis the clipping parameter associated with the coefficient cf, that is determined by a clipping index The clipping parameter btmay be derived as follows:( 2BDwhen cb = 0 .... b-={L(bl1[2BD~1~2diotherwise where BD denotes the sample bit depth, and rf, may be 0, 1 , 2 or 3.

[0137] Integer arithmetic may be employed. Let NUM_BITS denote the number of bits used to represent ALF filter coefficients ctas signed integers.

[0138] ALF filtering operations may be implemented as follows:offset » shift (6)where shift = NUM_BITS - 1and offset = 1 » (shift — 1) (8)

[0139] Online filter optimization and offline pre-training may be employed. ALF filter coefficients and clipping indices may be determined at encoding time by, for example, solving Wiener-Hopf equations to minimize the MSE between reconstructed samples and their original values at slice level. If a ratedistortion condition may be met, these coefficients and, if applicable, the corresponding clipping indices, may be encoded in an Adaptation Parameter Set (APS). For example, an ALF APS may contain one Luma filter set and up to 8 Chroma filters. Example encoders and decoders may reference up to 8 ALF APSs at the same time.

[0140] Pre-trained Luma filters may have been learned offline and may be hard-coded both at encoder and decoder side.

[0141] ALF may be employed for Luma. ALF for Luma may present a further local adaptation with a classification based on local gradients. ALF for Luma, therefore, may rely on filter sets which may be a plurality of filters that come together with a mapping list, each class of the classification being associated with a specific filter of the filter set. Depending on the classification, geometric filter transformations may be applied, such as, for example, 90-degree rotation, diagonal or vertical flip, so that same filter coefficients may apply to different classes / gradient directions.

[0142] A number of pre-trained Luma filter sets may be available at the encoder and decoder sides. The encoder may determine, e.g., choose, according to a rate-distortion criterion whether it shall transmit the Luma filter set that may have been optimized for the current slice / frame.

[0143] At the coding-tree unit (CTU) level, the encoder may determine if ALF is performed and may select the Luma filter set that may be, e.g., shall be, used between the pre-trained filter sets and the filter sets that may have already been transmitted.

[0144] In some examples, Chroma ALF may not implement local classification, but may use, e.g., may use instead, region-adapted filters. Up to 8 ALF Chroma filters may be available at the same time at encoder and decoder sides and each Chroma CTB may signal which filter it uses.

[0145] ALF may present further developments. An intermediate step may be introduced for Luma filtering which may comprise filtering reconstructed samples with pre-trained filters, which may be referred to as “fixed filters,” before proceeding with the online-trained adaptive filters. FIG. 7 depicts a workflow of example filtering. As shown, samples may undergo DBF processing before undergoing one of SAC, BIF, or CCSAO processing. The resulting samples may then undergo ALF processing.

[0146] In examples, there may be three fixed filters which may be denoted f0, and f2. Two of them, f0and / j, may be based on a local classification and may be quantization parameter (QP) dependent.

[0147] Classification-based fixed filters may be employed. Two Laplacian-based classifiers (one for each classification-based fixed filter) may be applied to a 2x2 block. In each classifier, activity and directionality values may be derived based on vertical, horizontal, and diagonal gradients using a window surrounding each 2x2 block. For each 2x2 block, the mean value of a surrounding window may be calculated. For each sample of this window, the difference between the sample value and the mean value may be calculated. A scaling factor may be determined based on the activity value derived from a Laplacian classifier. The square root of the sum of the squared differences may be further quantized to C by a scaling factor. The value of C may be an integer between 0 and 7, inclusively. Let Ctdenote theclass index provided by the 896-class Laplacian classifier of i-th fixed filter based on the activity and directionality values. The final class index 6 may be derived as:Q' = C x 896 +

[0148] Two double diamond-shaped fixed filters may be selected from the two fixed filter sets by using the derived two class indices Q and C The first fixed filter f0may be applied to sample values before DBF and ALF input, with an 13x13 diamond applying on ALF input and an additional 9x9 diamond applying to sample values before DBF. The second fixed filtermay be applied to output of f0and sample values before DBF using a 9x9 diamond on each.

[0149] Quantization Parameter (QP) dependent fixed ALF filters may be employed. Fixed filters f0and / j may be QP-dependent. For each fixed filter f0there may be eight different filter sets hard-coded at encoder and decoder sides with each of the filter sets applying for a given QP range. Each of these fixed filter sets may use its own bank of 512 pre-trained filters. The filter bank may be specific to a classifier (e.g., i=0 or 1) and to said QP range. FIG. 8 depicts example minimum (910) and maximum filter set (912) indices depending on QP. At encoding time, given the QP value for the current slice, the encoder may have the choice between two fixed filter sets, as illustrated in FIG. 8. The index of the fixed filter set selected for each CTU may be signaled in the bitstream.

[0150] Gaussian fixed filters may be employed. A third Luma fixed filter with a shape of diamond 7x7 may be used without classification. This fixed filter may be referred to as the Gaussian fixed filter.

[0151] Signaled Luma filter may be employed. After fixed filtering, a signaled Luma filter may be applied to the following: the ALF input samples; samples before the deblocking filter (DBF); outputs of the two classifications-based fixed filters; output of the Gaussian fixed filter; and the residual data.

[0152] The value of a final Luma filtered sample may be computed as follows:is the clipped difference between a neighboring sample and the current sample 7?(x,y); g8 iis the clipped difference between an intermediate sample generated from the first fixed filter and the current sample 7?(x, y); g2iiis the clipped difference between an intermediate sample generated from the third fixed filter and the current sample 7?(x, y) ; ^0,34 is the clipped difference between the collocated intermediate sample generated from first fixed filter and the current sample / ?(x, y); g1 35is the clipped difference between the collocated intermediate sample generated from second fixed filter and the current sample / ?(x, y); g2 39is the clipped difference between the collocated intermediate sample generated from third fixed filter and the current sample / ?(x, y); hf is the clipped difference between a neighboring sample before DBF and the current sample 7?(x, y); h36is the clipped difference between the collocated sample before DBF and the current sample 7?(x, y) , and where r37is the clipped neighboring residual sample value; and rFiltered38is the clipped residual sample filtered by a fixed- filter. For residual samples, the fixed filter may be a fixed filter from the first fixed filter set.

[0153] FIG. 9 depicts an example Luma ALF signaled filter shape. The complete filter shape of ALF using residual samples as additional inputs is shown in FIG. 9.

[0154] Alternative 2x2 ALF classifiers for Luma may be employed. Luma classification may be extended with an additional alternative classifier. For a signaled Luma filter set, a flag may be signaled to indicate whether the alternative classifier is applied. Geometrical transformation is not applied to the alternative band classifier. If the band-based classifier is applied, the sum of sample values of a 2x2 luma block may be calculated. The class index may then be calculated as below: class Jndex = (sum * 25) » (sample bit depth + 2) (11)

[0155] An example encoder design may be provided. An encoder may in a first place select a fixed filter set per classifier for each CTU based on a distortion comparison.

[0156] Based on those per-CTU decisions, statistics may be collected on the whole current slice in order to derive the coefficients and clipping indices of an optimal signaled filter set.

[0157] Depending on the signaling cost of that new optimal filter set and the corresponding quality gain on the slice, the encoder may determine, e.g., decide, to signal the new optimal filter set in an ALF APS. In examples, up to four Luma filter sets may be signaled in the same ALF APS.

[0158] Each CTU may signal which filter set it may use among every available filter set (e.g., the collection of every filter set of all referenced ALF APSs).

[0159] A plurality of pre-trained QP-specific filter sets may be available at encoder and decoder sides. However, only one filter set may have been used and the corresponding index may have been signaledin the bitstream. Improvements may be made.

[0160] In examples, Adaptive in-Loop Filtering (ALF) frameworks may present two successive steps: a first step using pre-trained, QP-specific, “fixed” filter sets (e.g., filters that may have been learned offline for a given QP range and that may be hard-coded both at encoder and decoder side); and a second filtering step using filters that are determined at encoding time and transmitted in the bitstream. Within this framework, for a given fixed filter, a plurality of QP-eligible fixed filter sets may be applied, and the respective results may be combined in an adaptive, e.g., a final adaptive, filtering outcome.

[0161] FIG. 10 depicts example processing for combining QP-eligible filters. A plurality of QP-specific pre-trained filters may be determined at 1110 to be available both at encoder and decoder sides. Depending on the current QP value, a subset of QP-eligible filters may be selected at 1112 and applied on adaptive filtering input samples. The outputs of the selected QP-eligible filters may be combined at 1114 to generate adaptive filtering output.

[0162] In examples, there may be no fixed filter set index to be signaled per CTU.

[0163] There may be several example implementations to combine the respective results of eligible fixed filters. Different implementations may be described herein.

[0164] In examples, the number of QP-eligible fixed filter sets may be equal to two.

[0165] Considering a given fixed filter, both QP-eligible fixed filter sets may be applied, and a weighting factor determined at encoding time may be signaled in the bitstream for each CTU in addition to ALF syntax elements that specify the signaled filter that is to be used.

[0166] Signals in the bitstream may be used to indicate whether a regular ALF process or the combined method is used.

[0167] One or more of the following example implementations may be employed: fixed filter fusion per CTU, with weighting factor(s) signaled per CTU, wherein two weighting factors (e.g., one per fixed filter) or a single weighting factor for both fixed filters may be employed; additional tap(s) in signaled filter shape, wherein variants may depend the fixed filters impacted; fixed filtering without classification wherein the filter set may come down to a single filter; combining more than two QP-eligible filters; fixed filter combination with derived weighting factors wherein a look-up table or straightforward computation may be employed.

[0168] A video encoding / decoding method may be employed where Adaptive in-Loop Filtering (ALF) may present two successive steps: a first step using pre-trained, QP-specific, “fixed” filter sets (e.g., filters that were trained offline for a given QP range, and that are hard-coded both at encoder and decoder side); and a second filtering step using filters that use the output of fixed filters. The filters may be determinedat encoding time and included in video data (e.g., transmitted in the bitstream).

[0169] In examples, given a fixed filter, a plurality of QP-eligible fixed filter sets may be applied. At least one fixed filter set index may be determined, for example, as follows: fixedFilterSetldx = [(QP — 2O) / 4J (12) where [. J denotes the floor function.

[0170] In examples, the number of QP-eligible fixed filter sets may be equal to two. The indices of the QP-eligible fixed filter sets may be, for example, fixedFilterSetldx and fixedFilterSetldx + 1), or (fixedFilterSetldx — 1) and fixedFilterSetldx.

[0171] Example implementations may combine the output of QP-eligible fixed filter sets in the final ALF outcome.

[0172] Fixed filter fusion per CTU using weighting factors may be employed. In examples, combining QP-eligible fixed filter sets outcome may rely on the signaling of at least one weighting factor at CTU level. A weighting factor may range from zero to one, inclusive, and may take intermediate values. The total number of values may be predetermined.

[0173] In an example, at least one weighting factor may be negative and / or at least one weighting factor may be superior to, e.g., above, one.

[0174] In an example, a weighting factor may be encoded as an unsigned integer with a given number of bits. In another example, the weighting factor may be encoded with a variable-length code. In yet another example, the weighting factor may be binarized and encoded with its own contexts by context- adaptive binary arithmetic coding (CABAC).

[0175] For CTUs or group of CTUs where the ALF flag is off, no weighting factor may be, e.g., needs to be, signaled.

[0176] In an example, a single weighting factor a may be signaled at CTU level.

[0177] Let Pinfand Psupdenote the outcome of signaled adaptive filtering using a lower fixed filter set index and using a higher fixed filter set index, respectively. The same index may be used for both fixed filters (for instance f0and ff), regardless of the classifier. The weighting factor may combine the outcome of QP-eligible fixed filter sets as follows:

[0178] One weighting factor per fixed filter may be employed. In examples, two weighting factors a0and a may be signaled at CTU level, where a0controls the merging of QP-eligible fixed filter sets for f0, and a controls the merging of QP-eligible fixed filter sets for f .

[0179] The output of ALF process may be defined as follows:where: ^infoinfidenotes the outcome of signalled adaptive filtering using lower fixed filter set index for both fixed filter f0and fixed filter - ^infoSupidenotes the outcome of signalled adaptive filtering using lower fixed filter set index for fixed filter f0and higher fixed filter set index for fixed filter / j; ^su^mfi denotes the outcome of signalled adaptive filtering using higher fixed filter set index for fixed filter f0and lower fixed filter set index for fixed filter / i; and ^supoinfldenotes the outcome of signalled adaptive filtering using higher fixed filter set index for both fixed filter f0and fixed filter f . In an example, the second weighting factor a may be differentially coded with respect to first weighting factor a0.

[0180] Processing may be performed at the encoder side. For each CTU, the encoder may determine jointly the best weighting factor(s) for combining QP-eligible fixed filter sets together with the best signaled filter set. This may be performed by a test, e.g., an exhaustive test, of every combination of every signaled filter set available together with every weighting factor value allowed.

[0181] Tap pairs for QP-eligible fixed filter output in a signaled filter may be employed. In examples, the signaled adaptive filter may be extended with at least one additional tap. At least one tap pair may apply as follows: a first tap may apply on the output of the QP-eligible fixed filter selected when using the lower fixed filter set index; a second tap may apply on the output of the QP-eligible fixed filter selected when using the higher fixed filter set index.

[0182] In the non-linear example, a ‘tap’ may refer to a filter coefficient and the corresponding clipping index. In the linear case, ‘tap’ may refer to a filter coefficient.

[0183] Additional filter coefficients and, if applicable, additional clipping indices may be determined at encoding time, for example, with an iterative optimization method relying on solving Wiener-Hopf system equations at slice level.

[0184] A single additional tap for a fixed filter may be employed. In an example, a single fixed filter, e.g., only fixed filter number 1 (#1), may apply two QP-eligible fixed filter sets.

[0185] In examples, the signaled adaptive filter may have 37 taps. Taps numbered 0 to 9 may apply on BIF / SAO output samples. Taps numbered 10 to 27, and number 30 may apply on fixed filter number 0 output samples. Taps number 31 and 32 may apply on fixed filter number 1’s lower and higher index QP-eligible fixed filter, respectively. Taps number 28-29 and 34 may apply on pre-DBF samples. Tapsnumber 33 and 35 may apply on residuals samples and filtered residual samples, respectively. Tap 36 may apply on fixed filter 2 output samples. An example of such a 37-tap signaled adaptive filter shape is provided in Figure 11 . FIG. 11 depicts an example of a 37-tap signaled adaptive filter shape presenting a tap pair for QP-eligi ble fixed filter sets for fixed filter number 1 .

[0186] In examples, the signaled filter may have 40 taps, where taps numbered 0 to 9 may apply on BIF / SAO output samples. Taps numbers 10-27 and number 34 may apply on fixed filter number 0 output samples. Taps number 35 and number 36 may apply on fixed filter number 1’s lower and higher index QP-eligible fixed filter, respectively. Taps numbers 28-31 and number 39 may apply fixed filer number 2 output samples. Taps numbers 32-33 and number 37 may apply on pre-DBF samples. Tap number 38 may apply on residual samples. An example of such a 40-tap signaled adaptive filter shape is depicted in FIG. 12. FIG. 12 depicts an example of a 40-tap signaled adaptive filter shape presenting a tap pair for QP-eligible fixed filter sets for fixed filter number 1 .

[0187] In examples, signaled adaptive filters may present tap pairs for both fixed filter number 0 and fixed filter number 1.

[0188] In examples, the fixed filter considered for combining QP-eligible filters may not rely on local sample classification. The classification may present a single class for every sample and filter sets may come down to a single filter.

[0189] In examples, more than two QP-eligible filters may be combined. In examples, three or more QP-eligible fixed filter sets may be combined. If three fixed filter sets are combined, the indices of the QP-eligible fixed filter sets may be, for example, fixedFilterSetldx - 1), fixedFilterSetldx, and fixedFilterSetldx + 1).

[0190] In examples where weighting factors are signaled at CTU level, group of CTUs, slice / picture level or sequence level, the number of weighting factors may be equal to the number of QP-eligible filters to be combined minus one. For example, in the case of three QP-eligible filters, ifinf,midandsupdenote the outcome of signaled adaptive filtering using lower, middle, and higher fixed filter set indices, respectively, the combination uses two weighting factors a and (3 as follows:

[0191] In examples, additional taps in signaled adaptive filter shape may be employed. If the fixed filters combination is performed directly during the step of signaled filter optimization, the combination may rely on tap tuples. For example, in the case of three QP-eligible filters, combining their respective results may rely on tap triplets.

[0192] Fixed filter combination with derived weighting factors (e.g., without signaling) may be provided.In examples, combining QP-eligible fixed filter sets outcome may rely on using weighting factors that are derived from information available at a decoder. In this example, the syntax cost for adaptive filtering may be reduced since no weighting factor needs to be signaled.

[0193] Look-up-tables (LUT) may be employed. In examples, weighting factors may be fetched in a Look-up Table (LUT). The LUT size may equal the divisor (e.g., the denominator) in the integer division of Equation (12).

[0194] T able 1 and T able 2 provide examples of such a LUT:Table 1 : Example of weighting factor Look-up TableTable 2: Another example of weighting factor Look-up Table

[0195] Accessing the LUT derives on the QP value, for instance as follows:LUTidx= QP - 20) - 4 X [(QP - 2O) / 4J (16) or:LUTidx= 3 - (QP - 20) - 4 X [(QP - 20) / 4j) (17) where [. J denotes the floor function.

[0196] In examples, weighting factors may be computed. The computation may involve, for example, the QP value.

[0197] In examples, if N=2, a weighting factor a may be derived as follows: a = fixedFilterSetId.Xfrac— [fixedFilterSet!dXfrac\ (18) or: a = 1 — (fixedFilterSet!dXfrac— [fixedFilterSet!dXfrac) (19) where fixedFilterSet!dxfracmay be a real or rational number depending on QP and may be stored as a floating-point number or as a fixed-point number that may, for example, be defined as: fixedFilterSetldx = (QP — 20) / 4 (20) and where [. J denotes the floor function.

[0198] The weighting factor a may be used to combine the outcome of QP-eligible fixed filter sets, for example, as in Equation (13).

[0199] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

CLAIMS1 . A video decoding device comprising: a processor configured at least to: determine a quantization parameter (QP) value; select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets; apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples; and combine the respective output samples.

2. The video decoding device of claim 1 , wherein the plurality of ALF QP-specific filter sets comprises two ALF QP-specific filter sets.

3. The video decoding device of claim 2, wherein the processor is further configured to: determine, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor.

4. The video decoding device of claim 3, wherein the processor configured to combine the respective output samples is further configured to apply a respective weighting factor to a corresponding one of the respective output samples.

5. The video decoding device of claim 1 , wherein the processor configured to combine the respective output samples is further configured to apply a signaled adaptive filter with at least one added tap.

6. The video decoding device of claim 2, wherein the processor is further configured to: derive, based on the QP value, a first weighting factor and a second weighting factor, and wherein the processor configured to combine the respective output samples is further configured to apply the first weighting factor to a first of the respective output samples and to apply the second weighting factor to a second of the respective output samples.

7. A video decoding method comprising:determining a quantization parameter (QP) value; selecting, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets; applying each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples; and combining the respective output samples.

8. The method of claim 7, wherein the plurality of ALF QP-specific filter sets comprises two ALF QP-specific filter sets.

9. The method of claim 8, wherein the method further comprises: determining, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor.

10. The method of claim 9, wherein combing the respective output samples further comprises applying a respective weighting factor to a corresponding one of the respective output samples.11 . The method of claim 7, wherein combining the respective output samples comprises applying a signaled adaptive filter with at least one added tap.

12. The method of claim 8, wherein the method further comprises: deriving, based on the QP value, a first weighting factor and a second weighting factor, and wherein combining the respective output samples comprises applying the first weighting factor to a first of the respective output samples and applying the second weighting factor to a second of the respective output samples.

13. A video encoding device comprising: a processor configured at least to: determine a quantization parameter (QP) value; select, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets; apply each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples; and combine the respective output samples.

14. The video encoding device of claim 13, wherein the plurality of ALF QP-specific filter sets comprises two ALF QP-specific filter sets.

15. The video encoding device of claim 14, wherein the processor is further configured to: determine, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor.

16. The video encoding device of claim 15, wherein the processor is further configured to send, for each CTU comprised in the video data, the respective weighting factor.

17. The video encoding device of claim 15, wherein the processor configured to combine the respective output samples is further configured to apply a respective weighting factor to a corresponding one of the respective output samples.

18. The video encoding device of claim 13, wherein the processor is further configured to determine an adaptive filter with at least one added tap; and wherein the processor configured to combine the respective output samples is further configured to apply the adaptive filter with at least one added tap.

19. The video encoding device of claim 18, wherein the processor is further configured to send an indication of the adaptive filter with at least one added tap.

20. The video encoding device of claim 14, wherein the processor is further configured to: derive, based on the QP value, a first weighting factor and a second weighting factor, and wherein the processor configured to combine the respective output samples is further configured to apply the first weighting factor to a first of the respective output samples and to apply the second weighting factor to a second of the respective output samples.21 . A video encoding method comprising: determining a quantization parameter (QP) value; selecting, based on the QP value, a plurality of adaptive loop filter (ALF) QP-specific filter sets; applying each of the plurality of ALF QP-specific filter sets to video samples associated with video data to generate respective output samples; and combining the respective output samples.

22. The method of claim 21 , wherein the plurality of ALF QP-specific filter sets comprises two ALF QP-specific filter sets.

23. The method of claim 22, further comprising: determining, for each Coding-Tree Unit (CTU) comprised in the video data, a respective weighting factor.

24. The method of claim 23, further comprising: sending, for each CTU comprised in the video data, the respective weighting factor.

25. The method of claim 23, wherein combining the respective output samples further comprises applying a respective weighting factor to a corresponding one of the respective output samples.

26. The method of claim 21 , further comprising: determining an adaptive filter with at least one added tap, wherein combining the respective output samples further comprises applying the adaptive filter with at least one added tap.

27. The method of claim 26, further comprising: sending an indication of the adaptive filter with at least one added tap.

28. The method of claim 22, further comprising: deriving, based on the QP value, a first weighting factor and a second weighting factor, and wherein combining the respective output samples further comprises applying the first weighting factor to a first of the respective output samples and applying the second weighting factor to a second of the respective output samples.

29. A computer program product stored on a computer readable medium and comprising program code instructions for implementing the steps of a method according to any one of claims 7 through 12 and claims 21 through 28 when executed by a processor.

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