Adaptive range clipping

Abstract

Adaptive range clipping for color components of image data is described. During decoding, for example, range bound information can be determined from a first header within an encoded bitstream. The first header is a header that applies to multiple frames of a video sequence, and the range bound information includes at least one of an upper bound or a lower bound for values of at least one plane of color data. A value of a clip flag is determined from respective second headers within the encoded bitstream. A second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the portion. The multiple frames are selectively decoded using the range bound information and the value of the clip flag.

Description

ADAPTIVE RANGE CLIPPINGBACKGROUND

[0001] Digital video streams may represent video using a sequence of frames or still images. Digital video can be used for various applications including, for example, video conferencing, high-definition video entertainment, video advertisements, or sharing of usergenerated videos. A digital video stream can contain a large amount of data and consume a significant amount of computing or communication resources of a computing device for processing, transmission, or storage of the video data. Various approaches have been proposed to reduce the amount of data in video streams, including encoding or decoding techniques.SUMMARY

[0002] An aspect of the teachings herein is a method for using adaptive range clipping in video coding. Range bound information is determined from a first header within an encoded bitstream. The first header is a header that applies to multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of at least one plane of color data (e.g., the luma plane). The value of a clip flag is determined from respective second headers within the encoded bitstream. A second header is a header that applies to at least a portion of a frame of the multiple frames (e.g., a whole frame or slice), and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame. The multiple frames are selectively decoded using the range bound information from the first header and the value of the clip flag from the respective second headers.

[0003] In some implementations, the first header is signaled with a sequence parameter set, an adaptive parameter set, or a picture parameter set.

[0004] In some implementations, the second header is a frame header or a slice header.

[0005] In some implementations, selectively decoding the multiple frames includes reconstructing a first frame of the multiple frames using luma mapping by reconstructing luma blocks of the first frame in a mapped sample domain, modifying values for inverse luma mapping using the range bound information, wherein the inverse luma mapping converts mapped luma values from the mapped sample domain to an original sample domain,converting luma values of the luma blocks of the first frame from the mapped sample domain to the original sample domain using the inverse luma mapping as modified, and storing the first frame in the original sample domain for inter prediction.

[0006] In some variations of these implementations, the method includes performing at least one in-loop filtering process on the first frame after converting the luma values,

[0007] In some variations of these implementations, the method includes using the first frame for inter prediction of a luma block of a second frame after the first frame in a decoding order, modifying values for forward luma mapping using the range bound information, where the forward luma mapping converts luma code values in the original sample domain to the mapped sample domain, converting a predictor block resulting from the inter prediction from the original sample domain to the mapped sample domain using the forward luma mapping as modified, and providing the predictor block as converted to a reconstruction process for the second frame. After reconstructing the second frame, the values for the forward luma mapping may be restored. Modifying the values for the forward luma mapping may include modifying a forward luma mapping table that maps values in the original sample domain to values in the mapped sample domain.

[0008] In any of the above implementations, modifying the values for the inverse luma mapping can include modifying an inverse luma mapping table that maps values in the mapped sample domain to values in the original sample domain.

[0009] In any of the above implementations, the method can include restoring the values for the inverse luma mapping after converting luma values of the luma blocks of the first frame.

[0010] In any of the above implementations, the method can include reconstructing chroma blocks of the first frame in the original sample domain using chroma scaling.

[0011] In some of the above implementations, selectively decoding the multiple frames includes reconstructing luma blocks and chroma blocks of at least one frame using luma mapping and chroma scaling (LMCS).

[0012] An aspect of the teachings herein is another method for using adaptive range clipping in video coding. Range bound information is encoded into a first header of an encoded bitstream. The value of a clip flag is encoded into the respective second headers of the encoded bitstream. The multiple frames are selectively encoded using the range bound information of the first header and the value of the clip flag of the respective second headers.

[0013] An aspect of the teachings herein is yet another method for using adaptive range clipping in video coding. Range bound information is determined from an encoded bitstream.The range bound information applies to at least one frame of multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of a luma plane of color data. A value of a clip flag for at least a portion of a frame of the multiple frames is also determined from the encoded bitstream. The value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame. The multiple frames are selectively decoded using the range bound information and the value of the clip flag for respective portions of the frame using luma mapping by modifying values for inverse luma mapping using the range bound information, wherein the inverse luma mapping converts mapped luma values from a mapped sample domain to an original sample domain, modifying values for forward luma mapping using the range bound information, wherein the forward luma mapping converts luma code values in the original sample domain to the mapped sample domain, and performing clipping using the range bound information in the mapped sample domain (e.g., at prediction and / or reconstruction).

[0014] In some implementations of this method, performing clipping using the range bound information in the mapped sample domain includes performing clipping after at least one of prediction of a block or reconstruction of the block.

[0015] An aspect of the teachings herein is another method for using adaptive range clipping in video coding. Range bound information is encoded into a first header of an encoded bitstream. The first header is a header that applies to multiple frames of a video sequence, and the range bound information is an upper bound, a lower bound, or both, for values of at least one plane of color data. A value of a clip flag is encoded into respective second headers of the encoded bitstream. The second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame. Finally, the method includes selectively encoding the multiple frames using the range bound information of the first header and the value of the clip flag of the respective second headers.

[0016] An aspect of the teachings herein is a system or apparatus that can perform any of these methods and others described herein.

[0017] An aspect of the teachings herein is a non-transitory computer-readable storage medium storing an encoded bitstream. The encoded bitstream is configured to be encoded according to any of encoding methods described herein or to be decoded according to any of the decoding method described herein.

[0018] In some implementations, the encoded bitstream includes a first header that includes range bound information, wherein the first header applies to multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of at least one plane of color data, second headers that respectively include a value of a clip flag, wherein a second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame, and multiple frames that are selectively encoded using the range bound information of the first header and the value of the clip flag of respective second headers.

[0019] These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims, and the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The description herein makes reference to the accompanying drawings described below, wherein like reference numerals refer to like parts throughout the several views.

[0021] FIG. 1 is a schematic of a video encoding and decoding system.

[0022] FIG. 2 is a block diagram of an example of a computing device that can implement a transmitting station or a receiving station.

[0023] FIG. 3 is a diagram of a typical video stream to be encoded and subsequently decoded.

[0024] FIG. 4 is a block diagram of an encoder according to implementations of this disclosure.

[0025] FIG. 5 is a block diagram of a decoder according to implementations of this disclosure.

[0026] FIG. 6 is a flowchart diagram of a technique for video coding using adaptive range clipping.

[0027] FIG. 7 is a block diagram of a reconstruction path in which the techniques described herein may be implemented.DETAILED DESCRIPTION

[0028] Video compression schemes may include breaking respective images, or frames, of a video stream into smaller portions, such as coding tree blocks (CTBs) or coding tree units (CTUs) (sometimes referred to as superblocks), and generating an encoded bitstream using techniques to limit the information included for respective CTUs thereof. The bitstreamcan be decoded to re-create the source frames from the limited information. Encoding CTUs to or decoding CTUs from the bitstream can include predicting the values of pixels or CTUs based on similarities with other pixels or CTUs in the same frame or in one or more other frames that have already been coded.

[0029] Those similarities can be determined using intra prediction, which attempts to predict the pixel values of a coding unit (CU) (coding block, etc.) of a CTU using pixels peripheral to the CU (e.g., pixels that are in the same frame as the CU, but that are outside the CU). During encoding, the result of an intra-prediction mode performed against a CU is a prediction unit (PU) (prediction block, predictor block, etc.). A prediction residual can be determined based on a difference between the pixel values of the CU and the pixel values of the PU. The prediction residual and the intra-prediction mode used to ultimately obtain that prediction residual can then be encoded to a bitstream. During decoding, the prediction residual is reconstructed into a CU using a PU produced based on the intra-prediction mode and is thereafter included in an output video stream.

[0030] Similarly, inter prediction attempts to predict the pixel values of a CU of a CTU using pixels from one or more reference frames. During encoding, the result of an interprediction mode performed against a CU is also a PU. A prediction residual can be determined based on a difference between the pixel values of the CU and the pixel values of the PU. The prediction residual and the inter-prediction mode used to ultimately obtain that prediction residual can then be encoded to a bitstream. During decoding, the prediction residual is reconstructed into a CU using a PU produced based on the inter-prediction mode and is thereafter included in an output video stream.

[0031] A frame, and hence its CTUs and CUs may include a luminance, also referred to as luma, component and two chrominance, also referred to as chroma, components. These luma and chroma components may in some cases be referred to as luma blocks and chroma blocks. The luma component may, for example, be expressed within a Y plane and the chroma components may be expressed either within U and V planes or Cr and Cb planes. The luma component is understood to include some number of luma samples and each chroma component is understood to include some number of chroma samples. Generally, the luma samples provide measures of brightness throughout a frame and thus represent the structural qualities of the video content of the frame, whereas the chroma samples provide measures of color throughout the frame. The number of luma samples can indicate the spatial resolution (or simply the resolution) of the frame.

[0032] Adaptive clipping of the luma and chroma samples is possible. For example, value ranges (min and max) of the color (e.g., Y, U, V) components may be signaled separately at the picture (image, frame) level. The clip may be performed after prediction, reconstruction (i.e., after adding prediction blocks to residuals), and (e.g., in-loop) filtering. The signaling cost of adaptive clipping is high, and having clip everywhere (e.g., for every frame) is not needed.

[0033] Implementations of this disclosure describe adaptive range clipping that reduce signaling cost and provide flexible application of clip. Further details of techniques for video coding using adaptive range clipping are described herein with initial reference to a system in which they can be implemented.

[0034] FIG. 1 is a schematic of a video encoding and decoding system 100. A transmitting station 102 can be, for example, a computer having an internal configuration of hardware such as that described in FIG. 2. However, other implementations of the transmitting station 102 are possible. For example, the processing of the transmitting station 102 can be distributed among multiple devices.

[0035] A network 104 can connect the transmitting station 102 and a receiving station 106 for encoding and decoding of the video stream. Specifically, the video stream can be encoded in the transmitting station 102, and the encoded video stream can be decoded in the receiving station 106. The network 104 can be, for example, the Internet. The network 104 can also be a local area network (LAN), wide area network (WAN), virtual private network (VPN), cellular telephone network, or any other means of transferring the video stream from the transmitting station 102 to, in this example, the receiving station 106.

[0036] The receiving station 106, in one example, can be a computer having an internal configuration of hardware such as that described in FIG. 2. However, other suitable implementations of the receiving station 106 are possible. For example, the processing of the receiving station 106 can be distributed among multiple devices.

[0037] Other implementations of the video encoding and decoding system 100 are possible. For example, an implementation can omit the network 104. In another implementation, a video stream can be encoded and then stored for transmission at a later time to the receiving station 106 or any other device having memory. In one implementation, the receiving station 106 receives (e.g., via the network 104, a computer bus, and / or some communication pathway) the encoded video stream and stores the video stream for later decoding. In an example implementation, a real-time transport protocol (RTP) is used for transmission of the encoded video over the network 104. In another implementation, atransport protocol other than RTP may be used, e.g., video streaming protocol based on the Hypertext Transfer Protocol (HTTP).

[0038] When used in a video conferencing system, for example, the transmitting station 102 and / or the receiving station 106 may include the ability to both encode and decode a video stream as described below. For example, the receiving station 106 could be a video conference participant who receives an encoded video bitstream from a video conference server (e.g., the transmitting station 102) to decode and view and further encodes and transmits his or her own video bitstream to the video conference server for decoding and viewing by other participants.

[0039] FIG. 2 is a block diagram of an example of a computing device 200 that can implement a transmitting station or a receiving station. For example, the computing device 200 can implement one or both of the transmitting station 102 and the receiving station 106 of FIG. 1. The computing device 200 can be in the form of a computing system including multiple computing devices, or in the form of one computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like.

[0040] A processor 202 in the computing device 200 can be a conventional central processing unit. Alternatively, the processor 202 can be another type of device, or multiple devices, capable of manipulating or processing information now existing or hereafter developed. For example, although the disclosed implementations can be practiced with one processor as shown (e.g., the processor 202), advantages in speed and efficiency can be achieved by using more than one processor.

[0041] A memory 204 in computing device 200 can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. However, other suitable types of storage device can be used as the memory 204. The memory 204 can include code and data 206 that is accessed by the processor 202 using a bus 212. The memory 204 can further include an operating system 208 and application programs 210, the application programs 210 including at least one program that permits the processor 202 to perform the techniques described herein. For example, the application programs 210 can include applications 1 through N, which further include a video coding application that performs the techniques described herein. The computing device 200 can also include a secondary storage 214, which can, for example, be a memory card used with a mobile computing device.Because the video communication sessions may contain a significant amount of information,they can be stored in whole or in part in the secondary storage 214 and loaded into the memory 204 as needed for processing.

[0042] The computing device 200 can also include one or more output devices, such as a display 218. The display 218 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 218 can be coupled to the processor 202 via the bus 212. Other output devices that permit a user to program or otherwise use the computing device 200 can be provided in addition to or as an alternative to the display 218. When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display, or a light emitting diode (LED) display, such as an organic LED (OLED) display.

[0043] The computing device 200 can also include or be in communication with an image-sensing device 220, for example, a camera, or any other image-sensing device 220 now existing or hereafter developed that can sense an image such as the image of a user operating the computing device 200. The image-sensing device 220 can be positioned such that it is directed toward the user operating the computing device 200. In an example, the position and optical axis of the image-sensing device 220 can be configured such that the field of vision includes an area that is directly adjacent to the display 218 and from which the display 218 is visible.

[0044] The computing device 200 can also include or be in communication with a soundsensing device 222, for example, a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the computing device 200. The sound-sensing device 222 can be positioned such that it is directed toward the user operating the computing device 200 and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the computing device 200.

[0045] Although FIG. 2 depicts the processor 202 and the memory 204 of the computing device 200 as being integrated into one unit, other configurations can be utilized. The operations of the processor 202 can be distributed across multiple machines (wherein individual machines can have one or more processors) that can be coupled directly or across a local area or other network. The memory 204 can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the computing device 200. Although depicted here as one bus, the bus 212 of the computing device 200 can be composed of multiple buses. Further, the secondary storage 214 can be directly coupled to the other components of the computing device 200 or can beaccessed via a network and can comprise an integrated unit such as a memory card or multiple units such as multiple memory cards. The computing device 200 can thus be implemented in a wide variety of configurations.

[0046] FIG. 3 is a diagram of an example of a video stream 300 to be encoded and subsequently decoded. The video stream 300 includes a video sequence 302. At the next level, the video sequence 302 includes a number of adjacent frames 304. While three frames are depicted as the adjacent frames 304, the video sequence 302 can include any number of adjacent frames 304. The adjacent frames 304 can then be further subdivided into individual frames, for example, a frame 306. At the next level, the frame 306 can be divided into a series of planes or segments 308. The segments 308 can be subsets of frames that permit parallel processing, for example. The segments 308 can also be subsets of frames that can separate the video data into separate colors. For example, a frame 306 of color video data can include a luminance plane and two chrominance planes. The segments 308 may be sampled at different resolutions.

[0047] Whether or not the frame 306 is divided into segments 308, the frame 306 may be further subdivided into blocks 310, which can contain data corresponding to, for example, 16x16 pixels in the frame 306. The blocks 310 can also be arranged to include data from one or more segments 308 of pixel data. The blocks 310 can also be of any other suitable size such as 4x4 pixels, 8x8 pixels, 16x8 pixels, 8x16 pixels, 16x16 pixels, or larger. Unless otherwise noted, the terms block and macroblock are used interchangeably herein.

[0048] FIG. 4 is a block diagram of an encoder 400 according to implementations of this disclosure. The encoder 400 can be implemented, as described above, in the transmitting station 102, such as by providing a computer software program stored in memory, for example, the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the transmitting station 102 to encode video data in the manner described in FIG. 4. The encoder 400 can also be implemented as specialized hardware included in, for example, the transmitting station 102. In one particularly desirable implementation, the encoder 400 is a hardware encoder.

[0049] The encoder 400 has the following stages to perform the various functions in a forward path (shown by the solid connection lines) to produce an encoded or compressed bitstream 420 using the video stream 300 as input: an intra / inter prediction stage 402, a transform stage 404, a quantization stage 406, and an entropy encoding stage 408. The encoder 400 may also include a reconstruction path (shown by the dotted connection lines) to reconstruct a frame for encoding of future blocks. In FIG. 4, the encoder 400 has thefollowing stages to perform the various functions in the reconstruction path: a dequantization stage 410, an inverse transform stage 412, a reconstruction stage 414, and a loop filtering stage 416. Other structural variations of the encoder 400 can be used to encode the video stream 300.

[0050] When the video stream 300 is presented for encoding, respective adjacent frames 304, such as the frame 306, can be processed in units of blocks. At the intra / inter prediction stage 402, respective blocks can be encoded using intra-frame prediction (also called intra prediction) or inter- frame prediction (also called inter prediction). In any case, a prediction block can be formed. In the case of intra prediction, a prediction block may be formed from samples in the current frame that have been previously encoded and reconstructed. In the case of inter prediction, a prediction block may be formed from samples in one or more previously constructed reference frames.

[0051] Next, the prediction block can be subtracted from the current block at the intra / inter prediction stage 402 to produce a residual block (also called a residual). The transform stage 404 transforms the residual into transform coefficients in, for example, the frequency domain using block-based transforms. The quantization stage 406 converts the transform coefficients into discrete quantum values, which are referred to as quantized transform coefficients, using a quantizer value or a quantization level. For example, the transform coefficients may be divided by the quantizer value and truncated.

[0052] The quantized transform coefficients are then entropy encoded by the entropy encoding stage 408. The entropy-encoded coefficients, together with other information used to decode the block (which may include, for example, syntax elements such as used to indicate the type of prediction used, transform type, motion vectors, a quantizer value, or the like), are then output to the compressed bitstream 420. The compressed bitstream 420 can be formatted using various techniques, such as variable length coding (VLC) or arithmetic coding. The compressed bitstream 420 can also be referred to as an encoded video stream or encoded video bitstream, and the terms will be used interchangeably herein.

[0053] The reconstruction path (shown by the dotted connection lines) can be used to ensure that the encoder 400 and a decoder 500 (described below with respect to FIG. 5) use the same reference frames to decode the compressed bitstream 420. The reconstruction path performs functions that are like functions that take place during the decoding process (described below with respect to FIG. 5), including dequantizing the quantized transform coefficients at the dequantization stage 410 and inverse transforming the dequantized transform coefficients at the inverse transform stage 412 to produce a derivative residualblock (also called a derivative residual). At the reconstruction stage 414, the prediction block that was predicted at the intra / inter prediction stage 402 can be added to the derivative residual to create a reconstructed block. The loop filtering stage 416 can be applied to the reconstructed block to reduce distortion such as blocking artifacts.

[0054] Other variations of the encoder 400 can be used to encode the compressed bitstream 420. In some implementations, a non-transform based encoder can quantize the residual signal directly without the transform stage 404 for certain blocks or frames. In some implementations, an encoder can have the quantization stage 406 and the dequantization stage 410 combined in a common stage.

[0055] FIG. 5 is a block diagram of a decoder 500 according to implementations of this disclosure. The decoder 500 can be implemented in the receiving station 106, for example, by providing a computer software program stored in the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the receiving station 106 to decode video data in the manner described in FIG. 5. The decoder 500 can also be implemented in hardware included in, for example, the transmitting station 102 or the receiving station 106.

[0056] The decoder 500, similar to the reconstruction path of the encoder 400 discussed above, includes in one example the following stages to perform various functions to produce an output video stream 516 from the compressed bitstream 420: an entropy decoding stage 502, a dequantization stage 504, an inverse transform stage 506, an intra / inter prediction stage 508, a reconstruction stage 510, a loop filtering stage 512, and a post filtering stage 514. Other structural variations of the decoder 500 can be used to decode the compressed bitstream 420.

[0057] When the compressed bitstream 420 is presented for decoding, the data elements within the compressed bitstream 420 can be decoded by the entropy decoding stage 502 to produce a set of quantized transform coefficients. The dequantization stage 504 dequantizes the quantized transform coefficients (e.g., by multiplying the quantized transform coefficients by the quantizer value), and the inverse transform stage 506 inverse transforms the dequantized transform coefficients to produce a derivative residual that can be identical to that created by the inverse transform stage 412 in the encoder 400. Using header information decoded from the compressed bitstream 420, the decoder 500 can use the intra / inter prediction stage 508 to create the same prediction block as was created in the encoder 400 (e.g., at the intra / inter prediction stage 402).

[0058] At the reconstruction stage 510, the prediction block can be added to the derivative residual to create a reconstructed block. The loop filtering stage 512 can be applied to the reconstructed block to reduce blocking artifacts. Other filtering can be applied to the reconstructed block. In this example, the post filtering stage 514 is applied to the reconstructed block to reduce blocking distortion, and the result is output as the output video stream 516. The output video stream 516 can also be referred to as a decoded video stream, and the terms will be used interchangeably herein. Other variations of the decoder 500 can be used to decode the compressed bitstream 420. In some implementations, the decoder 500 can produce the output video stream 516 without the post filtering stage 514 or otherwise omit the post filtering stage 514.

[0059] As mentioned initially, adaptive clipping may be used to keep pixel values within a range of values. The value ranges for luma and chroma color components may be separately signaled at the picture level and applied at different points in the reconstruction process at an encoder and decoder. For example, the different points may be after prediction at the intra / inter prediction stage 402, 508, reconstruction stage 414, 510, and loop filtering stage 416, 512. In some implementations of adaptive clipping, only a value range for the luma components is signaled, and the clipping may be applied at the same points or at different points such as before and after the loop filtering stage 416, 512. For example, in a video signal that conforms to the International Telecommunication Union Radiocommunication Sector (ITU-R) BT.2020 specification, only luma code values between 64 to 940 are allowed for a 10-bit narrow-range video. In either case (value ranges for luma only or for all color components), the signaling cost is high, especially because clipping is not needed in all situations.

[0060] FIG. 6 is a flowchart of a technique 600 for video coding using adaptive range clipping. The technique 600 can be implemented, for example, as a software program that may be executed by computing devices such as transmitting station 102 or receiving station 106. The software program can include machine-readable instructions that may be stored in a memory such as the memory 204 or the secondary storage 214, and that, when executed by a processor, such as the processor 202, may cause the computing device to perform the technique 600. The technique 600 may be implemented at least in part in the reconstruction stage of an encoder and / or the reconstruction path of a decoder. The technique 600 can be implemented using specialized hardware or firmware. Multiple processors, memories, or both, may be used.

[0061] At operation 602, range bound information is determined for at least one plane of color data. The range bound information may be a minimum value, a maximum value, or both, for one or more planes of color data. For example, the range bound information may be a minimum value (also referred to as a lower bound) and a maximum value (also referred to as an upper bound) for pixel values of a luma plane, a minimum value and a maximum value for pixels values of one or both chroma planes, or both. In some examples, the range bound information may include a minimum value or a maximum value for pixel values of a luma plane, a minimum value or a maximum value for pixels values of one or both chroma planes, or both, and the other value of the range may be inferred. For example, if a maximum value is transmitted, the minimum value may be inferred to be 0. Other examples are possible.

[0062] At a decoder, the range bound information is determined from a first header for multiple frames at operation 602. That is, the range bound information may be decoded from the first header (e.g., by entropy decoding). The first header for multiple frames is a header that applies to or is available to multiple frames. Stated differently, the first header includes coding parameters and other information that was used to encode and can be used to decode at least some frames of the multiple frames. The multiple frames can be any grouping of frames. For example, the frames may comprise a group of pictures (GOP). In some implementations, the first header is signaled with a sequence parameter set (SPS), an adaptive parameter set (APS), or a picture parameter set (PPS).

[0063] At operation 604, the technique 600 determines, from respective second headers of at least a portion of a frame of the multiple frames, a value of a clip flag that indicates whether to apply the range bound information to the at least the portion of the frame. That is, a second header is a header that applies to or is available to at least a portion of a frame of the multiple frames. For example, the second header may be a frame header of a frame of the multiple frames such that the coding parameters of the frame header (such as the range bound information) apply to or are available to the entire frame. The second headers may be frame headers for each frame of the multiple frames. In this way, a clip flag may be included for each frame such that the value of the clip flag indicates whether the corresponding frame was encoded and should be decoded using the range bound information. The second headers may be below the frame level. For example, a respective second header may be included in a slice header or a tile header such that signaling a frame of the multiple frames includes multiple second headers and hence multiple clip flags. In other implementations, a clip flag may be signaled at a region (a group of blocks) level, such as at coding tree unit (CTU) or super block level (such as respective blocks of 128 x 128 pixels that are partitioned into codingblocks for prediction), the level of 2x2 CTUs / super block levels, a CTU (or super block) row, a CTU (or super block) column, and so on.

[0064] At a decoder, the value of a clip flag may be determined from respective second headers within the encoded bitstream at operation 604. That is, the value of a clip flag may be decoded from a second header (e.g., by entropy decoding). The value indicates whether the frame portion (blocks of a frame, a slice, a tile, etc.) to which the clip flag applies was encoded and should be decoded using the range bound information.

[0065] In some implementations, the value of a clip flag may be inferred instead of signaled. For example, where the clip flag is a binary flag, a value of 1 determined from the encoded bitstream may indicate to apply the range bound information to the corresponding portion of a frame, and the omission of the clip flag indicates the value is 0 such that the range bound information is not applied.

[0066] At operation 606, the multiple frames are selectively decoded using the range bound information from the first header and the value of the clip flag from the respective second headers. For example, this may include decoding a respective frame on a block-by- block basis according to the techniques described with regards to FIG. 5, while performing clipping before and / or after one or more stages of a reconstruction path as described previously. Selectively decoding thus means that clipping may be performed on some but not all frames of the multiple frames and on at least some regions of one or more frames as indicated by the value of respective clip flags. The multiple frames may be selectively decoded in a decoding order.

[0067] At an encoder, the techniques used to select the range bound information, if any, for sets of multiple frames of a video sequence and to select what portion(s), if any, of each frame of the multiple frames to assign a clip flag are not particularly limited. For example, this information may be decided arbitrarily or may be based on a particular standard / specification. Additionally, or alternatively, techniques that code and reconstruct frames according to different parameters, such as different values for the range bound information and clip flags, can be used and the results compared to determine the best set of parameters (e.g., the set of parameters that results in the lowest distortion, the fewest bits, or some combination thereof). For example, rate-distortion calculations can be used.

[0068] Regardless of how the range bound information and the values of the clip flags are selected, the encoder can encode, into a first header of an encoded bitstream, the range bound information. As described previously, the first header is a header that applies to multiple frames of a video sequence, and the range bound information comprises at least one of anupper bound or a lower bound for values of at least one plane of color data. The encoder can also encode, into respective second headers of the encoded bitstream, a value of a clip flag. As also described above, a second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame. Finally, the encoder selectively encodes the multiple frames using the range bound information of the first header and the value of the clip flag of the respective second headers. In an example where the output video should conform to the ITU-R BT.2020 specification, range bound information comprising a lower bound of 64 and an upper bound of 940 may be signaled for the luma plane in the first header of sets of multiple frames forming a video sequence, and the clip flag of all frames indicates to apply the range bound information.

[0069] As mentioned, the method, process, or technique 600 of FIG. 6 may be implemented in the reconstruction path of an encoder, such as the encoder 400, or a decoder, such as the decoder 500. FIG. 7 is a block diagram of another reconstruction path in which the techniques described herein, including the technique 600, may be implemented. The techniques can occur at a reconstruction path of both an encoder and a decoder, so FIG. 7 represents a portion of either an encoder or decoder. The structure of FIG. 7 shows a modification to the reconstruction paths of the encoder 400 and decoder 500 that separates a luma reconstruction path 700 from a chroma reconstruction path 702 to functionally illustrate use of the teachings herein with luma mapping and chroma sampling (LMCS). Luma mapping (LM) may be performed alone or with chroma scaling (CS). Inputs to the structure of FIG. 7 include, for example, entropy decoded residual values and any coding information needed to reconstruct the image data (e.g., on a block and / or frame basis), such as coding mode, filtering parameters, etc.

[0070] LM remaps the luma code values, and CS allows flexible adjustment between luma and chroma signals. LM aims to improve coding efficiency by reallocating the luma code values of the input video signal within the complete codeword range. As in the example of a video signal that conforms to the ITU-R BT.2020 specification, only luma code values between 64 to 940 are allowed for a 10-bit narrow-range video. This inefficient codeword utilization can be addressed by remapping, which allows for coding performance improvements. CS, when used, is intended to re-balance the impact of luma remapping on the relative luma / chroma coding bit costs. The flexible adjustment between luma and chroma signals can be achieved by enabling or disabling CS at, e.g., the sequence or picture level, orfurther adjusting chroma scaling by applying a chroma scaling offset (deltaCRS, which can be signaled in a header).

[0071] LM maps the luma code values (or simply, luma values) of an input video signal from an original (unmapped) sample domain to a mapped sample domain. As shown in FIG. 7, the processes in the mapped sample domain (gray-shaded blocks) include inverse quantization at a dequantization stage 710, inverse transform at an inverse transform stage 712, luma intra prediction at an intra prediction stage 714, and reconstruction at a reconstruction stage 716. The dequantization stage 710 performs inverse quantization as described with regards to the dequantization stage 410 and the dequantization stage 504. The inverse transform stage 712 performs an inverse transform as described with regards to the inverse transform stage 412 and the inverse transform stage 506. The intra prediction stage 714, unlike the intra / inter prediction stages 402, 508 of FIGS. 4 and 5, is shown separately from an inter prediction stage 724 (discussed below) because of the differences in their processing. The reconstruction stage 716 reconstructs a luma block by summing the luma residual values from the inverse transform stage 712 with the luma prediction values from either the intra prediction stage 714 or the inter prediction stage 712 as discussed in more detail below.

[0072] In luma reconstruction, the processes in the original sample domain include inloop filtering (as described below) at a loop filtering stage 720, inter prediction at the inter prediction stage 724, and storage of pictures in a decoded picture buffer (DPB) 722. The look filtering stage 720 can be similar to the loop filtering stage 416 and the loop filtering stage 512 and is discussed in more detail below. Inverse luma mapping at an inverse luma mapping stage 718 maps the luma code values from the mapped sample domain to the original sample domain, and forward luma mapping at a forward luma mapping stage 726 maps the luma code values from the original sample domain to the mapped sample domain.

[0073] In the luma reconstruction path 700, the following steps are performed for LM. First, inverse quantization and inverse transform are applied to the decoded luma transform coefficients (e.g., obtained by entropy decoding) to produce the luma residues (or residuals) Y'res in the mapped sample domain. The processes of inverse quantization and inverse transform may be performed as described above with regards to the dequantization stage 410, 504 and the inverse transform stage 412, 506, respectively.

[0074] Thereafter, reconstructed luma sample values Y' in the mapped sample domain are obtained by summing Y'reSwith the corresponding predicted luma values Y'pred in the mapped sample domain at the reconstruction stage 716. When intra mode is signaled for prediction ofa portion (e.g., a block) of the frame, the predicted luma values Y'Pred are directly obtained by performing intra prediction in the mapped sample domain at the intra prediction stage 714. In contrast, when inter mode is signaled for prediction of the portion of the frame, the predicted luma values Ypred in the original sample domain are first obtained by motion compensation in the inter prediction stage 724 using reference pictures from the DPB 722, and then forward luma mapping (discussed in more detail below) is applied by the forward luma mapping stage 726 to produce the luma values Y'pred in the mapped sample domain. The prediction processes are performed as described above in the intra / inter prediction stage 402, 508.

[0075] The reconstructed values, which result from adding Y'pred and Y'reSat the reconstruction stage 716, are then inverse-mapped (e.g., using inverse luma mapping at the inverse luma mapping stage 718 as discussed in more detail below) and processed by loop filtering (using in-loop filters) at the loop filtering stage 720 before being stored in the DPB 722 in the original sample domain. In-loop filters are discussed in more detail below. The stored picture is then used for inter prediction of one or more frames after the current frame in the coding sequence.

[0076] The processes of chroma reconstruction all occur in the original sample domain as is conventional when CS is not performed. As mentioned, CS is optional. For example, CS may be disabled for chroma blocks with area size less than or equal to 4 samples.

[0077] CS, when performed, includes the following steps performed in the chroma reconstruction path 702 in the original sample domain. First, the inverse quantization and inverse transform processes at the dequantization stage 710 and inverse transform stage 714, respectively, are applied to the decoded chroma transform coefficients to produce chroma residue-scaled values CresScaie. Chroma residue (or residual) values Cresare obtained from the chroma scaling stage 730 by multiplying CresScaie by the inverse scaling factor invScaleC. The inverse scaling factor invScaleC may be determined based on a chroma scaling offset deltaCRS (e.g., a signaled value) and an average reconstructed luma value avgY' in the mapped sample domain from one or more neighboring coding units or blocks. Reconstructed chroma sample values Crare obtained by summing chroma residual values Creswith the corresponding predicted chroma values Cpred at a reconstruction stage 732. Predicted chroma values CPred are determined as described with regards to the predicted luma values, namely based on the prediction mode at a prediction stage like the intra / inter prediction stage 402, 508 described above. As with the luma reconstruction path 700, the intra prediction stage 734 and the inter prediction stage 736 within the chroma reconstruction path 702 are not shown as combined, although they can be.

[0078] After reconstruction at the reconstruction stage 732, the reconstructed chroma samples (e.g., a block, frame, etc.) may be filtered at a loop filtering stage 738. A filtered frame is stored as a picture in a decoded picture buffer (DPB) 740. The DPB 740 and the DPB 722 may be the same structure.

[0079] In these examples, the in-loop filtering process may be performed at one or more loop filtering stages of an encoder or decoder, such as the loop filtering stage 416 of FIG. 4 or the loop filtering stage 512 of FIG. 5. The loop filtering stages 720, 738 may be separate or combined. In either event, in-loop filtering may include filtering techniques such as deblocking (DBF), sample adaptive offset (SAG), adaptive loop filter (ALF), or some combination thereof. Broadly, these filtering techniques are used to reduce distortion introduced by encoding.

[0080] More specifically, a deblocking filter is designed to smooth sharp edges between blocks (CTUs and / or CUs) of the frame. This is sometimes referred to as removing blocking artifacts. The deblocking filter is generally applied to the entire reconstructed picture. For example, the rules, parameters, etc., for deciding whether to modify a pixel value and how to modify a pixel value at an edge are established on a frame-level basis. For example, one of multiple (e.g., three) filter strengths may be signaled. The deblocking filter may be applied to an 8x8 sample grid, a 4x4 sample grid, or some other size grid. The deblocking filter may first apply horizontal filtering for vertical edges of the picture and thereafter apply vertical filtering for horizontal edges of the picture, or vice versa. In some implementations of a codec (i.e., an encoder and decoder combination), the deblocking filter is applied before other in-loop filtering, if any, but this is not required.

[0081] SAO filtering also reduces distortion by compensating the pixel value offset between reconstructed pixels and original pixels. In general, SAO filtering classifies reconstructed pixels and adds a respective offset to each class or group of pixels. SAO may use different offsets pixel sample by pixel sample in a region depending on the sample classification, and SAO parameters may vary from region to region. The offsets may be determined at a decoder using, e.g., a look up table that is based on a histogram analysis made by the encoder. The region size may be fixed to one coding tree block (CTB) (or coding tree unit). That is, the SAO parameters may be signaled at CTB level.

[0082] More than one SAO type may be available for use. For example, an edge offset (EO) type and a band offset (BO) type may be available. The EO type may have multiple sub-types corresponding to processing along different directions. For example, the EO type may have four sub-types corresponding to processing along the horizontal, vertical, 135-degree, and 45-degree directions. For an EO sub-type, the value of a pixel (also called a sample) is compared to two of its neighbors using one of four different gradient patterns to classify the pixel. An offset is applied to pixels in each of the four gradient patterns. No offset may be applied for pixel values that do not match one of the gradient patterns. The BO type may be based where the sample values fall within multiple bands (such as 32 bands for values 0-255 in 8-bit coding). An offset is applied to pixels in at least some of the bands, which offset is determined for respective bands. Each color component of the picture may have its own SAO parameters. The SAO filtering can increase edge sharpness and reduce ringing and impulse artifacts.

[0083] Filtering performed by an ALF may be selectively performed before or preferably after SAO filtering. An ALF can minimize the mean squared error between an original picture and the reconstructed picture, such as the picture output from SAO filtering, to improve the quality of the reconstruction. The ALF is generally referred to as adaptive because the coefficients may be signaled in the bitstream so they can be designed to reflect the content and distortion of the reconstructed picture. Filtering may be performed generally by partitioning sample locations into classes and applying (e.g., Wiener) filters on a class basis. The filter shapes may differ for luma and chroma components. For example, a 7 x 7 diamond shape may be used for luma components, and a 5 x 5 diamond shape may be used for chroma components.

[0084] With regards to classification within ALF filtering, respective sub-blocks of the luma plane, such a 4 x 4 luma block, can be classified based on its directionality and two- dimensional (2D) Laplacian activity. The 2D Laplacian activity uses calculated gradients in multiple directions for the reconstructed luma samples, such in the horizontal, vertical, 135- degree, and 45-degree directions. Up to 25 classes may be used. Lor each used class, a filter is signaled from encoder to decoder.

[0085] In addition to this luma sub-block-level filter adaptation, ALE may incorporate superblock (CTB or CTU)-level filter adaptation (CC-ALE). A luma block can use a filter set calculated for the current slice or one of the filter sets calculated for a previously coded slice. The luma block can also use one of multiple (e.g., 16) offline trained filter sets. Within each luma CTB, which filter from the chosen filter set should be applied to each 4 x 4 block is determined by the class calculated for that block. With regards to chroma blocks, ALE may only use CTB-level filter adaptation. Each CTB can select one of a number of filters available to it for its chroma components. Lor example, up to 8 filters can be used for chroma components in a slice such that each CTB can select one of these filters.

[0086] The filtering described above is by example only. More, fewer, or different filters may be used for filtering in an encoder and decoder.

[0087] Adaptive range clipping may be combined with the LM process by modifying values for the inverse luma mapping and modifying values for the forward luma sampling using the adaptive range (e.g., the signaled lower and upper bounds for the luma components). In some implementations, the values for the forward luma mapping are stored in a forward lookup table (also called a forward luma mapping table) fwdLut that maps values in the original sample domain to values in the mapped sample domain (e.g., at the forward luma mapping stage 726). Similarly, the values for the inverse luma mapping that maps values in the mapped sample domain to values in the original sample domain may be stored in an inverse lookup table (also called an inverse luma mapping table) invLut (e.g., at the inverse luma mapping stage 718). Accordingly, modifying the values for the forward luma mapping can include modifying the forward luma mapping table fwdLut according to:

[0088] fwdLut[y] = fwdLutf yi. ] when y < yi_; or

[0089] fwdLut[y] = fwdLut[yu] when y > yu.

[0090] In the above, yu and yu are signaled lower bound and upper bound, respectively, and y is the value in the original domain.

[0091] Similarly, modifying the values for the inverse luma mapping can include modifying the inverse luma mapping table invLut, where y' is the value in the mapped domain, according to:

[0092] invLut[y'] = yu when y' < fwdLut[yu]; or

[0093] invLut[y'] = yu when y' > fwdLut[yu].

[0094] When processing (e.g., decoding) the portion of the frame (e.g., the whole frame, a slice, etc.) is complete, the values for the forward luma mapping and / or the inverse luma mapping should be restored because, for the next picture / slice / portion, the mapping may or may not be modified. For example, the lookup tables should be reset to the unmodified version.

[0095] Further, when used with LM (i.e., LM is on), the adaptive range clipping described herein may be used in the mapped domain in certain stages. For example, in some implementations when LM is on, clipping with lower bound fwdLut[yL] and upper bound fwdLut[yu] is performed after any prediction in the mapped domain, such as after intra prediction, intra block copy (IBC) prediction, and palette prediction. Clipping may also be performed after adding prediction and residuals to form reconstructed blocks / coding units.Note that this clipping may be combined with existing clipping by simply replacing the bounds with fwdLut[yL] and fwdLut[yu].

[0096] In an example, the final prediction of a block may be a combined prediction from both mapped domain values and original domain values. Accordingly, the predictions (pixels forming one or more prediction blocks) from the mapped domain may be clipped, while the predictions from the original domain may be forward transformed using fwdLut.

[0097] When LM is off, or for in-loop filtering (e.g., deblocking, SAO, ALF), the signaled lower and upper bounds may be directly used in the clipping by using the bounds based on signaled bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.).

[0098] When the clip flag is signaled below the frame / picture / slice level, such as for a region including a group of blocks (CTU, CTB), and the value of the clip flag indicates that adaptive range clipping should be performed, the clip bounds are only applied to prediction and reconstruction of the blocks in that region. The clip bounds are not applied to any filtering process.

[0099] The teachings herein can improve coding efficiency by reducing the signaling burden of adaptive range clipping. Further, processing requirements can be reduced by selectively encoding and decoding using adaptive range clipping at frame level and lower. This allows adaptive range clipping to be omitted when such clipping is not needed.

[0100] For simplicity of explanation, the techniques herein are depicted and described as respective series of steps or operations. However, the steps or operations in accordance with this disclosure can occur in various orders and / or concurrently. Additionally, other steps or operations not presented and described herein may be used. Furthermore, not all illustrated steps or operations may be required to implement a technique in accordance with the disclosed subject matter.

[0101] The aspects of encoding and decoding described above illustrate some examples of encoding and decoding techniques. However, it is to be understood that encoding and decoding, as those terms are used in the claims, could mean compression, decompression, transformation, or any other processing or change of data.

[0102] The word “example” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as being preferred or advantageous over other aspects or designs. Rather, use of the word “example” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise or clearly indicated otherwise by the context, the statement“X includes A or B” is intended to mean any of the natural inclusive permutations thereof. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more,” unless specified otherwise or clearly indicated by the context to be directed to a singular form. Moreover, use of the term “an implementation” or the term “one implementation” throughout this disclosure is not intended to mean the same embodiment or implementation unless described as such.

[0103] Implementations of the transmitting station 102 and / or the receiving station 106 (and the algorithms, methods, instructions, etc., stored thereon and / or executed thereby, including by the encoder 400 and the decoder 500) can be realized in hardware, software, or any combination thereof. The hardware can include, for example, computers, intellectual property (IP) cores, application- specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors, or any other suitable circuit. In the claims, the term “processor” should be understood as encompassing any of the foregoing hardware, either singly or in combination. The terms “signal” and “data” are used interchangeably. Further, portions of the transmitting station 102 and the receiving station 106 do not necessarily have to be implemented in the same manner.

[0104] Further, in one aspect, for example, the transmitting station 102 or the receiving station 106 can be implemented using a general-purpose computer or general-purpose processor with a computer program that, when executed, carries out any of the respective methods, algorithms, and / or instructions described herein. In addition, or alternatively, for example, a special purpose computer / processor can be utilized that can contain other hardware for carrying out any of the methods, algorithms, or instructions described herein.

[0105] The transmitting station 102 and the receiving station 106 can, for example, be implemented on computers in a video conferencing system. Alternatively, the transmitting station 102 can be implemented on a server, and the receiving station 106 can be implemented on a device separate from the server, such as a handheld communications device. In this instance, the transmitting station 102, using an encoder 400, can encode content into an encoded video signal and transmit the encoded video signal to the communications device. In turn, the communications device can then decode the encoded video signal using a decoder 500. Alternatively, the communications device can decode content stored locally on the communications device, for example, content that was nottransmitted by the transmitting station 102. Other suitable transmitting and receiving implementation schemes are available. For example, the receiving station 106 can be a generally stationary personal computer rather than a portable communications device, and / or a device including an encoder 400 may also include a decoder 500.

[0106] Further, all or a portion of implementations of the present disclosure can take the form of a computer program product accessible from, for example, a computer-usable or computer-readable medium. A computer-usable or computer-readable medium can be any device that can, for example, tangibly contain, store, communicate, or transport the program for use by or in connection with any processor. The medium can be, for example, an electronic, magnetic, optical, electromagnetic, or semiconductor device. Other suitable mediums are also available.

[0107] The above-described embodiments, implementations, and aspects have been described to facilitate easy understanding of this disclosure and do not limit this disclosure. On the contrary, this disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation as is permitted under the law to encompass all such modifications and equivalent arrangements.

Claims

What is claimed is:

1. A method, comprising: determining, from a first header within an encoded bitstream, range bound information, wherein the first header is a header that applies to multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of at least one plane of color data; determining, from respective second headers within the encoded bitstream, a value of a clip flag, wherein a second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame; and selectively decoding the multiple frames using the range bound information from the first header and the value of the clip flag from the respective second headers.

2. The method of claim 1, wherein the first header is signaled with a sequence parameter set, an adaptive parameter set, or a picture parameter set.

3. The method of one of claim 1 or claim 2, wherein the second header is a frame header or a slice header.

4. The method of any one of claims 1 to 3, wherein selectively decoding the multiple frames comprises reconstructing a first frame of the multiple frames using luma mapping by: reconstructing luma blocks of the first frame in a mapped sample domain; modifying values for inverse luma mapping using the range bound information, wherein the inverse luma mapping converts mapped luma values from the mapped sample domain to an original sample domain; converting luma values of the luma blocks of the first frame from the mapped sample domain to the original sample domain using the inverse luma mapping as modified; and storing the first frame in the original sample domain for inter prediction.

5. The method of claim 4, comprising: performing at least one in-loop filtering process on the first frame after converting the luma values.

6. The method of claim 4, comprising: using the first frame for inter prediction of a luma block of a second frame after the first frame in a decoding order; modifying values for forward luma mapping using the range bound information, wherein the forward luma mapping converts luma code values in the original sample domain to the mapped sample domain; converting a predictor block resulting from the inter prediction from the original sample domain to the mapped sample domain using the forward luma mapping as modified; and providing the predictor block as converted to a reconstruction process for the second frame.

7. The method of claim 6, comprising: restoring the values for the forward luma mapping after reconstructing the second frame.

8. The method of claim 6, wherein modifying the values for the forward luma mapping comprises modifying a forward luma mapping table that maps values in the original sample domain to values in the mapped sample domain.

9. The method of any one of claims 4 to 8, wherein modifying the values for the inverse luma mapping comprises modifying an inverse luma mapping table that maps values in the mapped sample domain to values in the original sample domain.

10. The method of any one of claims 4 to 9, comprising: restoring the values for the inverse luma mapping after converting luma values of the luma blocks of the first frame.

11. The method of any one of claims 4 to 10, comprising: reconstructing chroma blocks of the first frame in the original sample domain using chroma scaling.

12. The method of any one of claims 1 to 3, wherein selectively decoding the multiple frames comprises:reconstructing luma blocks and chroma blocks of at least one frame using luma mapping and chroma scaling (LMCS).

13. The method of claim 1, wherein selectively selectively decoding the multiple frames comprises: modifying values for inverse luma mapping using the range bound information, wherein the inverse luma mapping converts mapped luma values from a mapped sample domain to an original sample domain; modifying values for forward luma mapping using the range bound information, wherein the forward luma mapping converts luma code values in the original sample domain to the mapped sample domain; and performing clipping using the range bound information in the mapped sample domain.

14. The method of claim 13, wherein performing clipping using the range bound information in the mapped sample domain comprises performing clipping after at least one of prediction of a block or reconstruction of the block.

15. A method, comprising: encoding, into a first header of an encoded bitstream, range bound information, wherein the first header is a header that applies to multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of at least one plane of color data; encoding, into respective second headers of the encoded bitstream, a value of a clip flag, wherein a second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame; and selectively encoding the multiple frames using the range bound information of the first header and the value of the clip flag of the respective second headers.

16. An apparatus including a processor configured to perform the method according to any one of claims 1 to 14.

17. A non-transitory computer-readable storage medium storing an encoded bitstream comprising a first header that includes range bound information, wherein the first headerapplies to multiple frames of a video sequence, and the range bound information comprises at least one of an upper bound or a lower bound for values of at least one plane of color data, second headers that respectively include a value of a clip flag, wherein a second header is a header that applies to at least a portion of a frame of the multiple frames, and the value of the clip flag indicates whether to apply the range bound information to the at least the portion of the frame, and multiple frames that are selectively encoded using the range bound information of the first header and the value of the clip flag of respective second headers.- l-

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