Image processing device and method for performing quality-optimized deblocking

Abstract

To provide an image processing device (501) for use in an image encoder and / or an image decoder, for deblocking a block edge between a first block and a second block of an image encoded with a block code.SOLUTION: The image processing device (501) comprises a filter (502) for filtering the block edge, configured to, for at least some of the pixels to be filtered, within a deblocking range from the block edge, the deblocking range being perpendicular to the block edge, determine a filtered pixel value from an original pixel value of the pixel and at least one further pixel value, determine a clipping value of the pixel, dependent upon a distance of the pixel from the block edge, and clip the filtered pixel value using the clipping value resulting in a deblocked pixel value.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to the field of image processing, for example, still image and / or video image coding. In particular, the present disclosure refers to improvements in deblocking filters. [Background technology]

[0002] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to the field of image processing, for example, still image and / or video image coding. In particular, the present disclosure refers to improvements in deblocking filters.

[0003] Video coding schemes such as H.264 / AVC and HEVC are designed around the successful principle of block-based hybrid video coding. Using this principle, an image is first partitioned into blocks, and then each block is predicted using intra- or inter-image prediction. These blocks are coded relative to neighboring blocks to approximate the original signal with a similar degree of similarity. Because only coded blocks approximate the original signal, differences between the approximations may cause discontinuities in the prediction and alter block boundaries. These discontinuities are attenuated by a deblocking filter. HEVC replaces the macroblock structure of H.264 / AVC with the concept of a coding tree unit (CTU) with a maximum size of 64x64 pixels. CTUs can be further partitioned into a quadtree decomposition scheme into smaller coding units (CUs), which can be subdivided down to a minimum size of 8x8 pixels. HEVC also introduces the concepts of prediction blocks (PBs) and transform blocks (TBs).

[0004] In HEVC, two filters are defined in the deblocking filter: a normal filter and a strong filter. The normal filter modifies at most two samples on either side of an edge. The strong one filters three additional samples along the edge, comparing them with a threshold. If all of these checks are correct, the strong filter is applied. The strong filter has a more intensive smoothing effect on samples along the edge and can modify at most three samples on either side of the edge.

[0005] ITU-T VCEG (Q6 / 16) and ISO / IEC MPEG (JTC1 / SC29 / WG11) are considering a next-generation video codec, namely Versatile Video Coding (VVC). This new video codec standard targets compression capabilities that significantly exceed those of the current HEVC standard (including its current and near-term extensions for screen content coding and high dynamic range coding). The groups are working together on this research effort in a joint collaboration known as the Joint Video Coding Research Team (JVET) to evaluate compression technology designs proposed by their experts in this field.

[0006] The VVC Test Model (VTM) describes features that are under test model study by the ITU-T VCEG and the ISO / IEC MPEG Joint Video Coding Research Team (JVET) as future evolutionary video coding technologies that will exceed the performance of HEVC. The deblocking filter currently used in VTM 2.0 is the same as that used in HEVC.

[0007] However, currently deblocking often leads to excessive smoothing or blurring, especially in areas that are not immediately adjacent to block edges, which leads to suboptimal and poor deblocking quality. Summary of the Invention

[0008] In view of the above-mentioned problems, the present disclosure aims to improve conventional deblocking filtering. The present disclosure aims to provide an image processing device that can perform deblocking filtering with optimized quality. Furthermore, the deblocking should be efficient and accurate.

[0009] Embodiments of the present disclosure are defined by the features of the independent claims and further advantageous implementations of the embodiments by the features of the dependent claims.

[0010] According to a first embodiment of the present disclosure, an image processing device for use in an image encoder and / or image decoder is provided for deblocking a block edge between a first coded block and a second coded block of an image encoded with a block code. The image processing device includes a filter for filtering the block edge, and is configured to determine, for at least some pixels to be filtered within a deblocking range from the block edge and perpendicular to the block edge, a filtered pixel value from the original pixel value of the pixel and at least one further pixel value, determine a clipping value for the pixel depending on the pixel's distance from the block edge, and clip the filtered pixel value using the clipping value to obtain a deblocked pixel value. This reduces the effect of excessive smoothing or blurring and significantly improves the quality of the deblocking. The image processing device may be a processing circuit for performing the operations described in the present disclosure. The processing circuit may include hardware and software. The processing circuit may, for example, include one or more processors and a non-volatile memory carrying program code for execution by the one or more processors. When executed by one or more processors, the program code directs the image processing device to perform respective operations.

[0011] Advantageously, the clipping value is the maximum allowed change between the original pixel value and the deblocked pixel value, which further limits excessive smoothing or blurring.

[0012] Further advantageously, clipping the filtered pixel value with the clipping value to obtain the resulting deblocked pixel value comprises setting the deblocked pixel value to the filtered pixel value if the absolute value of the difference between the filtered pixel value and the deblocked pixel value does not exceed the pixel's clipping value, setting the deblocked pixel value to the original pixel value plus the pixel's clipping value if the filtered pixel value exceeds the original pixel value plus the clipping value, and setting the deblocked pixel value to the original pixel value minus the pixel's clipping value if the filtered pixel value is less than the original pixel value minus the clipping value, which further improves the deblocking quality.

[0013] Advantageously, the filter is adapted to determine the clipping value of a pixel depending on the pixel's distance from the block edge by using a function or a look-up table, which allows for a very accurate setting of the clipping value and thus makes it possible to improve the deblocking quality even further.

[0014] Further advantageously, the filter is adapted to determine the clipping value of a pixel depending on the pixel's distance from the block edge by using a function that monotonically decreases with increasing distance from the block edge, which significantly reduces the effect of excessive smoothing or blurring with increasing distance from the block edge, thereby improving the deblocking quality.

[0015] Advantageously, the function is exponential, which results in a particularly high deblocking quality.

[0016] Preferably, the function is: tc'=tc+(tc>>i) tc' is the clipping value. tc is a constant value. i is the pixel distance from the block edge (403, 800). >> indicates a right shift, which allows for simple computation of exponential functions.

[0017] Another alternative exponential function that can be used is: tc'=((2*tc)>>i) tc' is the clipping value. tc is a constant value. i is the pixel distance from the block edge (403, 800). >> indicates a right shift, which allows for simple computation of exponential functions.

[0018] Alternatively, the function is a linear function, which allows for improved deblocking quality while at the same time minimizing computational complexity.

[0019] Advantageously, the function is: tc'=tc+(tc-(i*x) tc' is the clipping value. tc is a constant value. i is the pixel distance from the block edge (403, 800). x is a constant value, which allows for particularly simple calculation of linear functions.

[0020] Preferably, the filter is adapted so that, for each pixel to be filtered within a deblocking range from the block edge and perpendicular to the block edge, it determines a filtered pixel value from the pixel's original pixel value and at least one further pixel value, determines a clipping value for the pixel that depends on the pixel's distance from the block edge, and clips the filtered pixel value with the clipping value to obtain the resulting deblocked pixel value. Using the same calculation for each pixel to be filtered results in a particularly simple implementation.

[0021] Alternatively, the filter is adapted to determine whether the block edge needs to be filtered based on the fact that, in the case of a vertical block edge, the number of determined pixel columns is less than the number of pixel columns in the block surrounding the block edge, and based on the fact that, in the case of a horizontal block edge, the number of determined image rows is less than the number of pixel rows in the block surrounding the block edge. The filter is then adapted to, for each pixel to be filtered that is not in a determined pixel row or a determined pixel column in a deblocking range from the block edge and perpendicular to the block edge, determine a filtered pixel value from the pixel's original pixel value and at least one further pixel value, determine a clipping value for the pixel that depends on the pixel's distance from the block edge, and clip the filtered pixel value with the clipping value to obtain a resulting deblocked pixel value. The filter is further adapted to determine, for each pixel to be filtered that is in a determined pixel row or determined pixel column within a deblocking range from the block edge and perpendicular to the block edge, a filter pixel value from the pixel's original pixel value and at least one further pixel value, and clip the filtered pixel value with a constant clipping value to result in a deblocked pixel value. This means that, at the same time, pixel values that are not in the determined row or column are filtered with a range-dependent clipping value, while pixels within the determined row or column are filtered with a fixed clipping value. This further improves deblocking quality at the expense of increased computational complexity.

[0022] Advantageously, the filter has a filter tap length of 1, or at least 2, or at least 3, or at least 4, or at least 5, or at least 6, or at least 7, or at least 8, or at least 9, or at least 10, or at least 11, or at least 12, or at least 13, or at least 14, or at least 15, or at least 16 pixels, which allows the application of the present disclosure to a wide variety of different filter designs.

[0023] According to a second aspect of the present disclosure, there is provided an encoder for encoding an image, comprising an image processing device according to the first aspect of the present disclosure.

[0024] According to a third aspect of the present disclosure, there is provided a decoder for decoding an image, comprising an image processing device according to the first aspect of the present disclosure.

[0025] According to a fourth aspect of the present disclosure, there is provided a deblocking method for deblocking a block edge between a first coded block and a second coded block of an image encoded with a block code. The method includes the steps of: for at least some of the pixels to be filtered within a deblocking range from the block edge, the deblocking range being perpendicular to the block edge; determining a filtered pixel value from the original pixel value of the pixel and at least one further pixel value; determining a clipping value for the pixel depending on the pixel's distance from the block edge; and clipping the filtered pixel value with the clipping value to obtain a resulting deblocked pixel value. This reduces the effects of excessive smoothing or blurring and significantly improves the quality of the deblocking.

[0026] According to a fifth aspect of the present disclosure, there is provided an encoding method for encoding an image, comprising the deblocking method of the fourth aspect of the present disclosure.

[0027] According to a sixth aspect of the present disclosure, there is provided a decoding method for decoding an image, comprising the deblocking method according to the fourth aspect of the present disclosure.

[0028] Finally, according to a seventh aspect of the present disclosure there is provided a computer program having a program code for performing a method according to the fourth, fifth or sixth aspect of the present disclosure when the computer program runs on a computer.

[0029] The details of one or more embodiments are set forth in the accompanying drawings and description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

[0030] The following embodiments of the present disclosure will be described in more detail with reference to the accompanying figures and drawings. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a block diagram illustrating an example of a video encoder configured to implement embodiments of the present disclosure. [Figure 2] 1 is a block diagram illustrating an example structure of a video decoder configured to implement embodiments of the present disclosure. [Figure 3] 1 is a block diagram illustrating an example of a video encoding system configured to implement embodiments of the present disclosure. [Figure 4] Two exemplary coding blocks are shown. [Figure 5] 1 illustrates an embodiment of an image processing device of the present invention according to a first aspect of the present disclosure. [Figure 6] 3 shows an embodiment of an inventive encoder according to a second aspect of the present disclosure; [Figure 7] 3 shows an embodiment of a decoder of the present invention according to a third aspect of the present disclosure. [Figure 8] 10 illustrates an example block edge according to pixel values before deblocking filtering. [Figure 9]10 shows a flow diagram of an embodiment of an image processing method according to a fourth aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0032] In the following, the same reference signs refer to the same or at least functionally equivalent features. In some cases, different reference signs are used in different figures to refer to the same elements.

[0033] First, the general concept of image coding is clarified according to Figures 1 to 3. According to Figures 4 and 8, the disadvantages of conventional deblocking filters are illustrated. With reference to Figures 5 to 7, the structure and function of different embodiments of the device of the present invention are shown and explained. Finally, with reference to Figure 9, an embodiment of the method of the present invention is shown and explained. In the different figures, similar elements and reference numerals are partially omitted.

[0034] In the following description, reference is made to the accompanying drawings, which form a part of this disclosure and which show, for illustrative purposes, specific aspects of embodiments of the present disclosure or in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and have structural or logical changes not shown in the drawings. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0035] For example, it is understood that disclosure related to a described method may also apply to a corresponding device or system configured to perform the method, and vice versa. For example, when one or more particular method steps are described, a corresponding device may include one or more units, e.g., functional units (e.g., one unit that performs one or more steps, or multiple units that each perform one or more of the steps), that perform the described method steps, even if such one or more units are not explicitly described or shown in the figures. On the other hand, for example, when a particular apparatus is described based on one or more units, e.g., functional units, a corresponding method may include one step that performs the function of one or more units (e.g., one step that performs the function of one or more units, or multiple steps that each perform one or more functions of multiple units), even if one or more steps are not explicitly described or shown in the figures. Furthermore, it is understood that features of various illustrative embodiments and / or aspects described herein may be combined with each other, unless otherwise specified.

[0036] Video coding typically refers to the processing of a series of images that form a video or a video sequence. Instead of the term image, the terms frame or image may be used as synonyms in the field of video coding. Video coding has two parts: video encoding and video decoding. Video encoding is performed on the source side, which typically involves processing the original video image (e.g., by compression) to reduce the amount of data needed to represent the video image (for more efficient storage and / or transmission). Video decoding is performed on the destination side, which typically involves the reverse process compared to the encoder to reconstruct the video image. Embodiments that refer to "encoding" a video image (or general image, as described later) shall be understood to relate to both "encoding" and "decoding" the video image. The combination of the encoding and decoding parts is also referred to as a codec (encoding and decoding).

[0037] In the case of lossless video coding, the original video image can be reconstructed, i.e., the reconstructed video image has the same quality as the original video image (assuming there is no transmission or other data loss during storage or transmission). In the case of lossy video coding, further compression, e.g., by quantization, is performed to reduce the amount of data representing the video image, which cannot be fully reconstructed at the decoder, i.e., the quality of the reconstructed video image is lower or worse than that of the original video image.

[0038] Several video coding standards since H.261 belong to the group of "lossy hybrid video codecs" (i.e., they combine spatial and temporal prediction in the sample domain with 2D transform coding to apply quantization in the transform domain). Each image of a video sequence is typically partitioned into a set of non-overlapping blocks, and encoding is typically performed at the block level. That is, in an encoder, video is typically processed, i.e., encoded, at the block (video block) level, for example, by using spatial (intra-image) prediction and temporal (inter-image) prediction to generate a predictive block, subtracting the predictive block from a current block (the block currently being processed / to be processed) to obtain a residual block, transforming the residual block, and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression). Meanwhile, in a decoder, a reverse process compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for display. Furthermore, the encoder repeats the decoder processing loop so that both generate the same prediction (e.g., intra- and inter-prediction) and / or reconstruction for processing, i.e., encoding, subsequent blocks.

[0039] Video image processing (also referred to as motion image processing) and still image processing (the term processing includes encoding) share many concepts and techniques or tools, and in the following the term "image" will be used to refer to video images and / or still images of a video sequence (as explained above), although not necessarily, to avoid unnecessary repetition and distinction between video images and still images. In the case of descriptions referring only to still images (or still images), the term "still image" will be used.

[0040] In the following embodiments of the encoder 100, the decoder 200 and the encoding system 300 will be described with reference to FIGS. 1 to 3 before embodiments of the present disclosure are described in more detail with reference to FIGS.

[0041] FIG. 3 is a conceptual or schematic block diagram illustrating an embodiment of an encoding system 300, e.g., an image encoding system 300, comprising a source device 310 configured to provide encoded data 330, e.g., an encoded image 330, to a destination device 320, e.g., for decoding the encoded data 330.

[0042] The source device 310 comprises an encoder 100 or encoding unit 100, and may additionally, i.e. optionally, comprise an image source 312, a pre-processing unit 314, e.g., an image pre-processing unit 314, and a communication interface or communication unit 318.

[0043] Image source 312 may comprise or be, for example, any kind of image capture device for capturing real-world images and / or any kind of image generation device, such as a computer graphics processor for generating computer-animated images, or any kind of device for acquiring and / or providing real-world images, computer-animated images (e.g., screen content, virtual reality (VR) images), and / or any combination thereof (e.g., augmented reality (AR) images). In the following, all of these types of images, as well as any other type of image, will be referred to as "images" or "images" unless otherwise stated, while the previous explanation regarding the term "images," covering "video images" and "still images," still applies unless explicitly specified differently.

[0044] A (digital) image is or can be considered as a two-dimensional array or matrix of samples with intensity values. The samples in the array may also be called pixels (abbreviation for picture element) or pels. The number of samples in the horizontal and vertical directions (or axes) of the array or image defines the size and / or resolution of the image. For color representation, typically three color components are used, i.e., an image can be represented or may contain three sample arrays. In an RGB format or color space, an image has corresponding red, green, and blue sample arrays. However, in video coding, each pixel is typically represented in a luminance / chrominance format or color space, e.g., YCbCr, which includes a luminance component denoted Y (sometimes L is also used instead) and two chrominance components denoted Cb and Cr. The luminance (or simply luma) component Y represents lightness or gray-level intensity (e.g., as in a grayscale image), while the two chrominance (or simply chroma) components Cb and Cr represent chromaticity or color information components. Optionally, an image in YCbCr format has a luminance sample array of luminance sample values (Y) and two chrominance sample arrays of chrominance values (Cb and Cr). An image in RGB format may be converted or transformed to YCbCr format, or vice versa, a process also known as color conversion or transformation. If the image is monochrome, the image may have only a luminance sample array.

[0045] The image source 312 may be, for example, a camera for capturing images, a memory having or storing previously captured or generated images, e.g., an image memory, and / or any kind of interface (internal or external) for acquiring or receiving images. The camera may be, for example, a local or integrated camera integrated into the source device, and the memory may be, for example, a local or integrated memory integrated into the source device. The interface may be, for example, an external interface for receiving images from an external video source, e.g., an external image capturing device such as a camera, an external memory, or an external image generating device, e.g., an external computer graphics processor, computer, or server. The interface may be any kind of interface, e.g., a wired or wireless interface, an optical interface, following any proprietary or standardized interface protocol. The interface for acquiring the image data 312 may be the same interface as or part of the communication interface 318.

[0046] In distinguishing between the pre-processing unit 314 and the processing performed by the pre-processing unit 314 , the image or image data 313 may also be referred to as raw image or raw image data 313 .

[0047] The pre-processing unit 314 is configured to receive the (raw) image data 313 and perform pre-processing on the image data 313 to obtain a pre-processed image 315 or pre-processed image data 315. The pre-processing performed by the pre-processing unit 314 may comprise, for example, cropping, color format conversion (e.g., from RGB to YCbCr), color correction or noise removal.

[0048] The encoder 100 is configured to receive pre-processed image data 315 and provide encoded image data 171 (further details are described, for example, with reference to FIG. 1).

[0049] The communications interface 318 of the source device 310 may be configured to receive the encoded image data 171 and transmit it directly to another device, such as the destination device 320 or any other device for storage or direct reconstruction, or to store the encoded data 330 and / or process the encoded image data 171 before transmitting the encoded data 330 to another device, such as the destination device 320 or any other device for decoding or storage, respectively.

[0050] The destination device 320 comprises a decoder 200 or decoding unit 200 , and may additionally, i.e. optionally, comprise a communication interface or communication unit 322 , a post-processing unit 326 , and a display device 328 .

[0051] The communication interface 322 of the destination device 320 is configured to receive the encoded image data 171 or the encoded data 330, for example, directly from the source device 310 or from any other source, for example, a memory, for example, an encoded image data memory.

[0052] The communication interface 318 and the communication interface 322 may each be configured to transmit and receive the encoded image data 171 or the encoded data 330 via a direct communication link between the source device 310 and the destination device 320, such as a direct wired or wireless communication, or via any type of network, such as a wired or wireless network or any combination thereof, or any type of private and public network, or any combination thereof.

[0053] The communications interface 318 may be configured, for example, to package the encoded image data 171 into an appropriate format, e.g., packets, for transmission over a communications link or network, and may further include data loss protection and data loss recovery.

[0054] Communications interface 322, which forms the other half of communications interface 318, may be configured, for example, to depackage encoded data 330 to obtain encoded image data 171, and may further be configured to perform data loss protection and recovery, including, for example, error concealment.

[0055] As indicated by the arrows for encoded image data 330 in FIG. 3 pointing from source device 310 to destination device 320, both communication interface 318 and communication interface 322 may be configured as unidirectional or bidirectional communication interfaces, or may be configured, for example, to send and receive messages, for example, to set up connections, confirm and / or retransmit lost or delayed data including image data, and exchange any other information related to the communication link and / or data transmission, e.g., encoded image data transmission.

[0056] The decoder 200 is configured to receive the encoded image data 171 and provide decoded image data 231 or a decoded image 231 (further details are described, for example, with reference to FIG. 2).

[0057] The post-processor 326 of the destination device 320 is configured to post-process the decoded image data 231, e.g., the decoded image 231, to obtain post-processed image data 327, e.g., the post-processed image 327. The post-processing performed by the post-processing unit 326 may include, for example, color format conversion (e.g., from YCbCr to RGB), color correction, cropping or resampling, or any other processing to prepare, for example, the decoded image data 231, for display by, for example, the display device 328.

[0058] The display device 328 of the destination device 320 is configured to receive the post-processed image data 327, for example, to display the image to a user or viewer. The display device 328 may be or include any type of display for presenting the reconstructed image, for example, an integrated or external display or monitor. The display may include, for example, a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, any type of other display... projector, hologram (3D)...

[0059] 3 depicts source device 310 and destination device 320 as separate devices, device embodiments may also have both or both functionality, source device 310 or corresponding functionality, and destination device 320 or corresponding functionality. In such embodiments, source device 310 or corresponding functionality and destination device 320 or corresponding functionality may be implemented using the same hardware and / or software, or by separate hardware and / or software, or any combination thereof.

[0060] As will be clear to those skilled in the art based on the description, the presence and (exact) division of functions or functions of different units within the source device 310 and / or destination device 320 as shown in FIG. 3 may vary depending on the actual device and application.

[0061] Therefore, the source device 310 and destination device 320 as shown in FIG. 3 are merely exemplary embodiments of the present disclosure, and embodiments of the present disclosure are not limited to those shown in FIG.

[0062] The source device 310 and the destination device 320 may comprise any of a wide range of devices, including any type of handheld or fixed device, e.g., a notebook or laptop computer, a mobile phone, a smartphone, a tablet or tablet computer, a camera, a desktop computer, a set-top box, a television, a display device, a digital media player, a video game console, a video streaming device or broadcast receiving device, etc. (also, e.g., servers and workstations for large-scale professional encoding / decoding, e.g., network entities), and may or may not use any type of operating system.

[0063] 1 shows a schematic / conceptual block diagram of an embodiment of an encoder 100, e.g., an image encoder 100, comprising an input 102, a residual calculation unit 104, a transform unit 106, a quantization unit 108, an inverse quantization unit 110 and an inverse transform unit 112, a reconstruction unit 114, a buffer 116, a loop filter 120, a decoded picture buffer (DPB) 130, prediction units 160 (inter estimation unit 142, inter prediction unit 144, intra estimation unit 152, intra prediction unit 154), a mode selection unit 162, an entropy encoding unit 170, and an output 172. The video encoder 100 as shown in FIG. 1 may also be referred to as a hybrid video encoder or a video encoder related to a hybrid video codec.

[0064] For example, the residual calculation unit 104, the transform unit 106, the quantization unit 108, and the entropy encoding unit 170 form the forward signal path of the encoder 100, while for example, the inverse quantization unit 110, the inverse transform unit 112, the reconstruction unit 114, the buffer 116, the loop filter 120, the decoded picture buffer (DPB) 130, the inter prediction unit 144, and the intra prediction unit 154 form the backward signal path of the encoder, which corresponds to the signal path of the decoder (see decoder 200 in Figure 2).

[0065] The encoder is configured to receive, for example, via input 102, an image 101 or an image block 103 of image 101, e.g. an image of a series of images forming a video or a video sequence. Image block 103 may also be referred to as a current image block or an image block to be coded, and image 101 may also be referred to as a current image or a picture to be coded (especially in video coding, which distinguishes the current image from other images, e.g. previously encoded and / or decoded images of the same video sequence, i.e. the video sequence in which the current image also resides).

[0066] An embodiment of encoder 100 may, for example, comprise a partitioning unit (not shown in FIG. 1 ), which may also be referred to as an image partitioning unit, configured to partition image 103 into a number of blocks, e.g., blocks such as block 103, typically into a number of non-overlapping blocks. The partitioning unit may be configured to use the same block size for all images of the video sequence and a corresponding grid that defines the block sizes, or to vary the block size between images or between subsets or groups of images, and partition each image into corresponding blocks.

[0067] Like image 101, block 103 is also of smaller dimensions than image 101, but is or can be considered as a two-dimensional array or matrix of samples having intensity values (sample values). That is, block 103 may have, for example, one sample array (e.g., a luma array in the case of monochrome image 101), or three sample arrays (e.g., a luma and two chroma arrays in the case of color image 101), or any other number and / or type of arrays, depending on the color format applied. The number of samples in the horizontal and vertical directions (or axes) of block 103 defines the size of block 103.

[0068] An encoder 100 as shown in FIG. 1 is arranged to encode an image 101 block by block, for example encoding and prediction is performed block by block 103 .

[0069] The residual calculation unit 104 is configured to calculate the residual block 105 based on the image block 103 and the prediction block 165, for example by subtracting sample values of the prediction block 165 from sample values of the image block 103 to obtain the residual block 105 in the sample domain on a sample-by-sample (pixel-by-pixel) basis (further details regarding the prediction block 165 are provided later).

[0070] The transform unit 106 is configured to apply a transform, such as a spatial-frequency transform or a linear spatial transform, such as a discrete cosine transform (DCT) or a discrete sine transform (DST), to the sample values of the residual block 105 to obtain transformed coefficients 107 in a transform domain. The transformed coefficients 107, also referred to as transformed residual coefficients, may represent the residual block 105 in the transform domain.

[0071] The transform unit 106 may be configured to apply an integer approximation of a DCT / DST, such as the core transform specified in HEVC / H.265. Compared to an orthonormal DCT transform, such an integer approximation is typically scaled by a constant factor. To preserve the norm of the residual block processed by the forward and inverse transforms, an additional scaling factor is applied as part of the transform process. The scaling factor is typically selected based on certain constraints, such as a scaling factor that is a power of two for shift operations, the bit depth of the transformed coefficients, a trade-off between accuracy and implementation cost, etc. A specific scaling factor may be specified for, e.g., an inverse transform, e.g., by the inverse transform unit 212 in the decoder 200 (and a corresponding inverse transform, e.g., by the inverse transform unit 112 in the encoder 100), and a corresponding scaling factor for, e.g., a forward transform, e.g., by the transform unit 106 in the encoder 100, may be specified accordingly.

[0072] The quantization unit 108 is configured to quantize the transformed coefficients 107, for example, by scalar quantization or vector quantization, to obtain quantized coefficients 109. The quantized coefficients 109 may also be referred to as quantized residual coefficients 109. For example, for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. A smaller quantization step size corresponds to finer quantization, and a larger quantization step size corresponds to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may, for example, be an index into a predefined set of applicable quantization step sizes. For example, a small quantization parameter may correspond to fine quantization (small quantization step size) and a large quantization parameter may correspond to coarse quantization (large quantization step size), or vice versa. Quantization may involve division by a quantization step size, and the corresponding or inverse dequantization, eg, by inverse quantizer 110, may involve multiplication by the quantization step size.

[0073] Embodiments of HEVC may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on the quantization parameter using a fixed-point approximation of a formula involving division. Additional scaling factors may be introduced for quantization and inverse quantization to restore the norm of the residual block, and may be modified by the scaling used in the fixed-point approximation of the formula for the quantization step size and the quantization parameter. In one exemplary implementation, the scaling of the inverse transform and inverse quantization may be combined. Alternatively, customized quantization tables may be used, e.g., signaled from the encoder to the decoder in the bitstream. Quantization is a lossy operation, and the larger the quantization step size, the greater the loss.

[0074] An embodiment of the encoder 100 (or the respective quantization unit 108) may be configured to output, for example, a quantization scheme and a quantization step size using corresponding quantization parameters, such that the decoder 200 may receive and apply the corresponding inverse quantization. An embodiment of the encoder 100 (or the quantization unit 108) may be configured to output, for example, an entropy-encoded quantization scheme and a quantization step size, either directly or via the entropy encoding unit 170 or any other entropy coding unit.

[0075] The inverse quantization unit 110 is configured to apply the inverse quantization of the quantization unit 108 to the quantized coefficients, e.g., by applying the inverse of the quantization scheme applied by the quantization unit 108, based on or using the same quantization step size as the quantization unit 108, to obtain the inverse quantized coefficients 111. The inverse quantized coefficients 111 may also be referred to as the inverse quantized residual coefficients 111 and typically correspond to the transformed coefficients 108, although they are not identical to the transformed coefficients due to loss due to quantization.

[0076] The inverse transform unit 112 is configured to apply an inverse transform of the transform applied by the transform unit 106, such as an inverse discrete cosine transform (DCT) or an inverse discrete sine transform (DST), to obtain an inverse transformed block 113 in the sample domain. The inverse transformed block 113 may also be referred to as an inverse transformed dequantized block 113 or an inverse transformed residual block 113.

[0077] The reconstruction unit 114 is configured to combine the inverse transformed block 113 and the prediction block 165 to obtain a reconstructed block 115 in the sample domain, for example by adding the sample values of the decoded residual block 113 and the sample values of the prediction block 165 sample by sample.

[0078] Buffer unit 116 (or simply, "buffer" 116), e.g., line buffer 116, is configured to buffer or store the reconstructed blocks and their respective sample values, e.g., for intra-estimation and / or intra-prediction. In further embodiments, the encoder may be configured to use the unfiltered reconstructed blocks and / or their respective sample values stored in buffer unit 116 for any type of estimation and / or prediction.

[0079] Embodiments of encoder 100 may be configured, for example, such that buffer unit 116 is used not only for storing reconstructed blocks 115 for intra estimation 152 and / or intra prediction 154, but also for loop filter unit 120 (not shown in FIG. 1 ), and / or such that buffer unit 116 and decoded picture buffer unit 130 form one buffer. Further embodiments may be configured to use filtered blocks 121 and / or blocks or samples from decoded picture buffer 130 (both not shown in FIG. 1 ) as input or basis for intra estimation 152 and / or intra prediction 154.

[0080] Loop filter unit 120 (or, briefly, "loop filter" 120) is configured to filter reconstructed block 115, for example by applying a deblocking sample adaptive offset (SAO) filter or other filter, such as a sharpening or smoothing filter or a collaborative filter, to obtain filtered block 121. Filtered block 121 may also be referred to as filtered reconstructed block 121. Loop filter 120 is also referred to as a deblocking filter hereinafter.

[0081] An embodiment of the loop filter unit 120 may include a filter analysis unit and an actual filter unit (not shown in FIG. 1 ), where the filter analysis unit is configured to determine loop filter parameters for the actual filter. The filter analysis unit may be configured to apply fixed, predetermined filtering parameters to the actual loop filter, adaptively select filtering parameters from a set of predetermined filtering parameters, or adaptively calculate filtering parameters for the actual loop filter.

[0082] An embodiment of the loop filter unit 120 may have one or more filters (loop filters / components / sub-filters), e.g., one or more of different kinds or types of filters connected in series or in parallel or any combination thereof, each of which may have a filter analysis unit (not shown in FIG. 1 ), either individually or in conjunction with other filters of the plurality of filters, to determine respective loop filter parameters, e.g., as described in the previous paragraph.

[0083] An embodiment of the encoder 100 (each loop filter unit 120) may be configured to output entropy-encoded loop filter parameters, for example, directly or via the entropy encoding unit 170 or any other entropy coding unit, so that, for example, the decoder 200 may receive and apply the same loop filter parameters for decoding.

[0084] A decoded picture buffer (DPB) 130 is configured to receive and store the filtered block 121. The decoded picture buffer 130 may further be configured to store other previously filtered blocks, e.g., previously reconstructed and filtered blocks 121, of the same current picture or of a different picture, e.g., a previously reconstructed picture, and may provide a fully previously reconstructed, i.e., decoded, picture (and corresponding reference blocks and samples) and / or a partially reconstructed current picture (and corresponding reference blocks and samples), e.g., for inter-estimation and / or inter-estimation.

[0085] Further embodiments of the present disclosure may be configured to use previously filtered blocks of the decoded picture buffer 130 and corresponding filtered sample values for any type of estimation or prediction, e.g., intra and inter estimation and prediction.

[0086] The prediction unit 160, also referred to as block prediction unit 160, is configured to receive or obtain image block 103 (current image block 103 of current image 101) and decoded or at least reconstructed image data, e.g., reference samples of the same (current) image, from buffer 116 and / or decoded image data 231 of one or more previously decoded images from decoded image buffer 130, and process such data for prediction, i.e., to provide a prediction block 165, which may be an inter-predicted block 145 or an intra-predicted block 155.

[0087] The mode selection unit 162 may be configured to select a prediction mode (e.g., intra or inter prediction mode) and / or a corresponding prediction block 145 or 155 to be used as the prediction block 165 for the calculation of the residual block 105 and for the reconstruction of the reconstructed block 115.

[0088] Embodiments of mode selection unit 162 may be configured to select a prediction mode (e.g., from those supported by prediction unit 160) that provides the best match, or i.e., the smallest residual (smallest residual means high compression for transmission or storage), or the smallest signaling overhead (smallest signaling overhead means high compression for transmission or storage), or considers or balances both. Mode selection unit 162 may be configured to determine the prediction mode based on rate-distortion optimization (RDO), i.e., to select a prediction mode that provides the smallest rate-distortion optimization, or whose associated rate-distortion at least satisfies a prediction mode selection criterion.

[0089] The prediction process (eg, by prediction unit 160) and mode selection (eg, by mode select unit 162) performed by exemplary encoder 100 are described in more detail below.

[0090] As explained above, the encoder 100 is configured to determine or select a best or optimal prediction mode from a (predetermined) set of prediction modes, which may include, for example, intra-prediction modes and / or inter-prediction modes.

[0091] The set of intra prediction modes may, for example, include 32 different intra prediction modes, such as omnidirectional modes like DC (or average) mode and planar mode, or directional modes, as specified in H.264, or may include 65 different intra prediction modes, such as omnidirectional modes like DC (or average) mode and planar mode, or directional modes, as specified in H.265.

[0092] The set of inter prediction modes (or possibilities) depends on the available reference images (i.e., previous at least partially decoded images stored in DBP230) and other inter prediction parameters, for example, whether the entire reference image or only a portion thereof, for example, a search window area around the area of the current block of the reference image, is used to search for the best matching reference block, and / or, for example, whether pixel interpolation is applied, for example, 1 / 2 / semi-pel and / or 1 / 4-pel interpolation.

[0093] In addition to the above prediction modes, skip mode and / or direct mode may be applied.

[0094] The prediction unit 160 may further be configured to partition the block 103 into smaller block partitions or sub-blocks, for example, by repeatedly using quadtree partitioning (QT), binary tree partitioning (BT), ternary tree partitioning (TT) or any combination thereof, and to perform prediction for each of the block partitions or sub-blocks, for example, wherein the mode selection comprises a tree structure of the partitioned block 103 and a selection of a prediction mode to be applied to each of the block partitions or sub-blocks.

[0095] The inter estimation unit 142, also referred to as inter image estimation unit 142, is configured to receive or obtain, for inter estimation (or "inter image estimation"), the image block 103 (the current image block 103 of the current image 101) and the decoded image 231, or at least one or more previously reconstructed blocks, e.g., reconstructed blocks of one or more other / different previously decoded images 231. For example, a video sequence may comprise the current image and the previously decoded image 231, i.e., the current image and the previously decoded image 231 may be part of a series of images forming a video sequence, or may form a series of images.

[0096] The encoder 100 may be configured to, for example, select a reference block from multiple reference blocks of the same or different images of multiple other images, and provide the reference image (or reference image index, ...) and / or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block to the inter prediction unit 144 as inter estimation parameters 143. This offset is also called a motion vector (MV). Inter estimation is also called motion estimation (ME), and inter prediction is also called motion prediction (MP).

[0097] The inter prediction unit 144 is configured to obtain, eg, receive, the inter prediction parameters 143 and perform inter prediction based on or using the inter prediction parameters 143 to obtain the inter prediction block 145 .

[0098] Although Figure 1 shows two separate units (or stages) for inter-coding, namely inter-estimation 142 and inter-prediction 144, both functions may be performed when one (inter-estimation) requires / has to calculate an inter-prediction block (i.e., a so-called "kind of" inter-prediction 144) by, for example, storing the current best inter-prediction mode and the respective inter-prediction block, repeatedly testing all possible or predetermined subsets of possible inter-prediction modes, and using the current best inter-prediction mode and the respective inter-prediction block as the (final) inter-prediction parameters 143 and inter-prediction block 145 without performing inter-prediction 144 at another time.

[0099] The intra estimation unit 152 is configured to obtain, e.g., receive, the image block 103 (current image block) and one or more previously reconstructed blocks of the same image for intra estimation, e.g., reconstructed neighboring blocks. The encoder 100 may, for example, be configured to select an intra prediction mode from a plurality of (predetermined) intra prediction modes and provide it as intra estimation parameters 153 to the intra prediction unit 154.

[0100] An embodiment of the encoder 100 may be configured to select an intra-prediction mode based on an optimization criterion, such as minimum residual (e.g., the intra-prediction mode that provides the predicted block 155 that is most similar to the current image block 103) or minimum rate distortion.

[0101] The intra prediction unit 154 is configured to determine the intra prediction block 155 based on the intra prediction parameters 153 , eg, the selected intra prediction mode 153 .

[0102] Although Figure 1 shows two separate units (or stages) for intra coding, namely, intra estimation 152 and intra prediction 154, both functions may be performed when one (intra estimation) requires / has to calculate an intra prediction block (i.e., a so-called "kind of" intra prediction 154), for example, by storing the current best intra prediction mode and the respective intra prediction block, while repeatedly testing all possible or predetermined subsets of possible intra prediction modes, and using the current best intra prediction mode and the respective intra prediction block as the (final) intra prediction parameters 153 and intra prediction block 155 without performing intra prediction 154 at another time.

[0103] The entropy encoding unit 170 is configured to apply an entropy encoding algorithm or scheme (e.g., a variable length coding (VLC) scheme, a context-adaptive VLC scheme (CALVC), an arithmetic coding scheme, a context-adaptive binary arithmetic coding (CABAC)) individually or jointly (or neither) to the quantized residual coefficients 109, the inter-prediction parameters 143, the intra-prediction parameters 153, and / or the loop filter parameters to obtain encoded image data 171 that can be output by an output 172, e.g., in the form of an encoded bitstream 171.

[0104] FIG. 2 shows an exemplary video decoder 200 configured to receive encoded image data (e.g., an encoded bitstream) 171, for example, encoded by encoder 100, to obtain a decoded image 231.

[0105] The decoder 200 comprises an input 202, an entropy decoding unit 204, an inverse quantization unit 210, an inverse transform unit 212, a reconstruction unit 214, a buffer 216, a loop filter 220, a decoded image buffer 230, a prediction unit 260, an inter prediction unit 244, an intra prediction unit 254, a mode selection unit 260, and an output 232.

[0106] The entropy decoding unit 204 is configured to perform entropy decoding on the encoded image data 171 to obtain, for example, quantized coefficients 209 and / or decoded coding parameters (not shown in FIG. 2), such as (decoded) inter-prediction parameters 143, intra-prediction parameters 153 and / or loop filter parameters.

[0107] In an embodiment of the decoder 200, the inverse quantization unit 210, the inverse transform unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded image buffer 230, the prediction unit 260, and the mode selection unit 260 are configured to perform the inverse processes of the encoder 100 (and their respective functional units) to decode the encoded image data 171.

[0108] In particular, the inverse quantization unit 210 may be identical in function to the inverse quantization unit 110, the inverse transform unit 212 may be identical in function to the inverse transform unit 112, the reconstruction unit 214 may be identical in function to the reconstruction unit 114, the buffer 216 may be identical in function to the buffer 116, the loop filter 220 may be identical in function to the loop filter 220 (for an actual loop filter, the loop filter 220 typically does not have a filter analysis unit that determines filtering parameters based on the original image 101 or block 103, but rather receives or obtains (explicitly or implicitly) the filtering parameters used for encoding from, for example, the entropy decoding unit 204), and the decoded image buffer 230 may be identical in function to the decoded image buffer 130.

[0109] The prediction unit 260 may include an inter prediction unit 244 and an inter prediction unit 254, which may be identical in functionality to the inter prediction unit 144 and which may be identical in functionality to the intra prediction unit 154. The prediction unit 260 and the mode selection unit 262 are typically configured to perform block prediction and / or obtain the predicted block 265 solely from the encoded data 171 (without using any further information about the original image 101), and to receive or obtain (explicitly or implicitly) information about the prediction parameters 143 or 153 and / or the selected prediction mode, for example, from the entropy decoding unit 204.

[0110] The decoder 200 is configured to output the decoded image 230, for example via output 232, for presentation or viewing to a user.

[0111] Although embodiments of the present disclosure have been described primarily based on video coding, it should be noted that embodiments of the encoder 100 and decoder 200 (and, correspondingly, system 300) may be configured for still image processing or coding, i.e., processing or coding of individual images unrelated to any preceding or consecutive images as in video coding. Generally, when image processing coding is limited to a single image 101, not only inter estimation 142 and inter prediction 144, 242 are available. In most cases, not all other functions (also referred to as tools or techniques) of the video encoder 100 and video decoder 200, such as partitioning, transform (scaling) 106, quantization 108, inverse quantization 110, inverse transform 112, intra estimation 142, intra prediction 154, 254, and / or loop filtering 120, 220, and entropy coding 170 and entropy decoding 204, may be equally applied to still images.

[0112] This disclosure refers to a deblocking filter scheme, also referred to as a loop filter in FIGS.

[0113] 4 shows two exemplary coding blocks 401, 402 separated by a block edge 403. The coding blocks 401, 402 comprise pixel columns 402-407 and pixel rows 408-415. In particular, the block edges here are vertical block edges. In this example, the blocks have a size of 4x4 pixels. However, other block sizes may be used in implementation.

[0114] For each segment of the block boundary, a deblocking decision is made separately.

[0115] A powerful deblocking filter in HEVC is applied to smooth areas where block artifacts are more visible. The filtering mode modifies three samples from the block boundary and enables powerful low-pass filtering. A clipping operation is also performed for each sample. The reason for performing the clipping operation is to limit the amount of filtering to ensure there is no excessive filtering for lines that were not considered in the filtering decision. As shown in FIG. 4, pixel columns 405 and 406 are not used in the filtering or no-filtering decision. This is done for computational complexity reasons. Here, only decision pixel columns 404 and 407 are used to determine the filtering to be performed.

[0116] Below, a function for determining the deblocked pixel value is given.

number

[0117] P0', P1', P2' are the filtered pixel values corresponding to the original pixel values P0, P1 and P2 respectively, where the second index is omitted as shown in FIG.

[0118] The symbol ">>" indicates a right shift. A right shift corresponds to division by 2y, where y is the amount of the right shift. For example, in function 7.17, ">>3" indicates division by 23, which equals 8.

[0119] The modified sample values are then clipped to the range [Pi-2tc, Pi+2tc], where Pi is the pixel value of pixel i and tc is a constant value. tc may be derived, for example, from a table using the average quantization parameter QP as an index into the table. Typically, the higher the QP value, the larger the tc value.

[0120] 8 shows a typical blocking artifact at a block edge 800. It can be easily seen that samples P0 and Q0 have the most distortion, while samples further away from the block edge, for example samples P3 and Q3, tend to have less distortion.

[0121] Because all of the pixel values are clipped to the same clipping range [Pi-2tc, Pi+2tc], pixel values that are far from the block boundary, e.g., P3 and Q3, also use the same clipping range and therefore allow them to be modified within the same range as pixel values P0 and Q0. This constant clipping range results in samples that are far from the boundary being modified significantly, resulting in excessive smoothing or blurring, or possibly still incorrect deblocking filtering with loss of meaningful image content.

[0122] Instead of using a fixed clipping range for all pixel values, in accordance with the present disclosure, the clipping range is made adaptive, specifically, the clipping range is made adaptive from the distance of each pixel from the block edge.

[0123] Advantageously, a lookup table or function is used to determine the clipping value by which filtered pixel values are clipped. Preferably, such a function is a monotonically decreasing function based on the pixel's distance from the edge. The greater the sample's distance from the edge / boundary, the smaller the clipping value defined for the pixel. Thus, pixel values farther away from the block edge can have a smaller clipping value, thereby allowing them to have a smaller deviation after clipping compared to pixel values closer to the block edge. In this way, the amount of filtering is controlled, preventing excessive smoothing or blurring.

[0124] Advantageously, an exponential function is used to determine the clipping value, which may then be determined as follows: tc'=tc+(tc>>i) tc' is the clipping value. tc is a constant value. i is the pixel's distance from the block edge. >> indicates a right shift.

[0125] This results in the following equation for clipping the deblocked pixel values: P'a,b=(Pa,b-(tc+(tc>>i)) Pa,b+(tc+(tc>>i))). where: P'a,b is the deblocked pixel value of pixels a, b. a is the integer index of the pixel row. b is the integer index of the pixel column. Pa,b is the original pixel value of pixels a and b. i is the integer distance in pixels from the block edge.

[0126] For example, for P0,0 and Q0,0, the value of i is 0 (the distance is 0), so clipping remains the same as described in equations 7.17-7.19. The clipping value is set to tc'=tc+(tc>>0)=2tc, resulting in P'0,0=(P0,0-2tc),P0,0+2tc).

[0127] For example, for P'1,0, clipping drops to tc'=tc+(tc>>1)=tc+tc / 2=1.5tc, resulting in P'1,0=(P1,0-1.5tc), P1,0+1.5tc).

[0128] For example, for P'2,0, clipping is reduced to tc'=tc+(tc>>2)=tc+tc / 4=1.25tc, resulting in P'2,0=(P2,0-1.25tc),P2,0+1.25tc).

[0129] As can be seen, the clipping value decreases progressively as the sample distance i increases from the block edge.

[0130] Another alternative exponential function that can be used is: tc'=((2*tc)>>i) tc' is the clipping value. tc is a constant value. i is the pixel's distance from the block edge. >> indicates a right shift.

[0131] This results in the following equation for clipping the deblocked pixel values: P'a,b=(Pa,b-((2*tc)>>i)) Pa,b+((2*tc)>>i))). where: P'a,b is the deblocked pixel value of pixels a, b. a is the integer index of the pixel row. b is the integer index of the pixel column. Pa,b is the original pixel value of pixels a and b. i is the integer distance in pixels from the block edge.

[0132] However, computing an exponential function results in significant computational complexity. In an alternative embodiment, a linear function may be used. In this case, the clipping value is set as follows: tc'=tc+(tc-(i*x) tc' is the clipping value. tc is a constant value. i is the pixel's distance from the block edge. x is a constant value.

[0133] This results in deblocked pixel values that are clipped. P'a,b= (Pa,b-(tc+(tc-(i*x)),Pa,b+(tc+(tc-(i*x))) where: P'a,b is the deblocked pixel value of pixels a, b. a is the integer index of the pixel row. b is the integer index of the pixel column. Pa,b is the original pixel value of pixels a and b. i is the integer distance in pixels from the block edge. x is a constant integer value.

[0134] Advantageously, x depends on the average quantization parameter QP used in the deblocking process. Generally, as the QP value increases, the value of x increases. Also, the value of x can be derived separately for 8-bit and 10-bit videos.

[0135] As an example, the value of x for 10-bit video can be set as follows: [Table 1] [Table 2] [Table 3] [Table 4]

[0136] As an example, for an average QP value of 37, the value of x is 2, so the pixel values are modified as follows:

[0137] For example, for P0,0, the value of i is 0 (the distance is 0), so clipping remains the same as described in equations 7.17-7.19. The clipping value is set to tc'=tc+(tc-(0*2)=2tc, resulting in P'0,0=(P0,0-(tc+(tc-(0*2)), P0,0+(tc+(tc-(0*2))).

[0138] For example, for P'1,0, clipping reduces to tc'=tc+(tc-(1*2)=2tc-2, resulting in P'1,0=(P1,0-2tc-2),P1,0+2tc-2)).

[0139] For example, for P'2,0, clipping reduces to tc'=tc+(tc-2*2)=tc+(tc-4)=2tc-4, resulting in P'2,0=(P2,0-(2tc-4)),P2,0+(2tc-4)).

[0140] In a further advantageous embodiment, the use of distance-dependent clipping is limited to non-determined pixel columns and non-determined pixel rows, as shown in FIG. 4, as previously indicated. As previously explained, the number of pixels from the determined pixel column (vertical block edge) or determined pixel row (horizontal block edge) is used to determine whether block edge filtering is performed. However, to reduce computational complexity, not all pixel columns / rows in the block are used as the basis for this determination. However, range-dependent clipping is performed only on non-determined pixel columns / rows, not on pixel columns / rows that are determined pixel columns / rows. Conventional clipping using a constant value is performed on the determined pixel columns / rows.

[0141] An embodiment of the first aspect of the present disclosure is shown in Figure 5. In particular, there is shown an image processing device 501 comprising a filter 502. The filter 502 is adapted to perform the deblocking filtering indicated above.

[0142] An embodiment of the second aspect of the present disclosure is shown in Figure 6. In particular, there is shown an encoder 600 comprising an image processing device 601, which further comprises a filter 602. As indicated above, the filter 602 performs deblocking filtering.

[0143] An embodiment of the third aspect of the present disclosure is shown in Figure 7. In particular, there is shown a decoder 700 comprising an image processing device 701, which in turn comprises a filter 702. As indicated above, the filter 702 performs deblocking filtering.

[0144] Finally, Fig. 9 shows a flow diagram of an embodiment of the fifth aspect of the present disclosure. In a first stage 1000, for at least some of the pixels to be filtered within a deblocking range from a block edge, a filtered pixel value is determined from the original pixel value of the pixel and at least one further pixel value. In a second stage 1001, a clipping value of the pixel is determined depending on the pixel's distance from the block edge. In a final third stage 1002, the filtered pixel value is clipped using the clipping value, resulting in a deblocked pixel value.

[0145] It is noted that the details from above regarding how deblocking filtering is performed are also applicable to the method according to the fourth aspect of the present disclosure.

[0146] It is important to note that the present disclosure is not limited to the embodiments, in particular the coding block sizes and filter tap lengths shown above: the present disclosure may be applied to any coding block size and any filter tap length.

[0147] [Definition of initials] CTU / CTB - Coding Tree Unit / Coding Tree Block CU / CB - Coding Unit / Coding Block PU / PB - Prediction Unit / Prediction Block TU / TB - Conversion Unit / Conversion Block HEVC - High Efficiency Video Coding

[0148] [List of reference numbers] Figure 1 100 Encoder 103 Image Block 102 Input (e.g., input port, input interface) 104 Residual Calculation [Unit or Step] 105 Residual Blocks 106 Transformations (e.g., with additional scaling) [units or steps] 107 Conversion Factor 108 Quantization [units or steps] 109 quantization coefficients 110 Inverse Quantization [units or steps] 111 Inverse quantization coefficients 112 Inverse transformation (e.g., with additional scaling) [units or steps] 113 Inverse transformed blocks 114 Reconstruction [unit or stage] 115 reconstructed blocks 116 (line) buffer [unit or stage] 117 Reference Samples 120 Loop Filter [Unit or Stage] 121 Filtered Blocks 130 Decoded Picture Buffer (DPB) [unit or step] 142 Inter-estimation (or Inter-image estimation) [unit or stage] 143 Inter estimation parameters (e.g., reference image / reference image index, motion vector / offset) 144 Inter-prediction (or Inter-image prediction) [unit or stage] 145 Inter-prediction blocks 152 Intra-estimation (or intra-image estimation) [unit or stage] 153 Intra prediction parameters (e.g., intra prediction mode) 154 Intra prediction (intra-frame / image prediction) [unit or stage] 155 intra-prediction blocks 162 Mode Selection [Unit or Stage] 165 predicted block (either inter-predicted block 145 or intra-predicted block 155) 170 Entropy Encoding [Unit or Stage] 171 Encoded image data (e.g., bitstream) 172 Output (output port, output interface) 231 decoded images Figure 2 200 decoder 171 Encoded image data (e.g., bitstream) 202 Input (Port / Interface) 254 Entropy Decoding 209 Quantization Coefficients 210 Inverse quantization 211 Inverse quantization coefficients 212 Inverse transformation (scaling) 213 Inverse transformed blocks 214 Reconstruction (Unit) 215 reconstructed blocks 216 (line) buffer 217 Reference Sample 220 Loop Filter (In-Loop Filter) 221 Filtered Blocks 230 Decoded Picture Buffer (DPB) 231 decoded images 232 Outputs (Ports / Interfaces) 244 Inter Prediction (Inter Frame / Image Prediction) 245 Inter Prediction Blocks 254 Intra Prediction (Intra Frame / Image Prediction) 255 intra prediction blocks 260 Mode Selection 265 predicted block (inter-predicted block 245 or intra-predicted block 255) Figure 3 300 Coding System 310 Source Device 312 Image Source 313 (Raw) Image Data 314 Preprocessor / Preprocessing Unit 315 Preprocessed image data 318 Communication Unit / Interface 320 Destination Device 322 Communication Unit / Interface 326 Postprocessor / Post-processing unit 327 Post-processed image data 328 display devices / units 330 Transmitted / Received / Communicated (Encoded) Image Data Figure 4 401 coding block 402 coding blocks 403 Block Edge 404 pixel rows 405 pixel rows 406 pixel rows 407 pixel rows 408 pixel rows 409 pixel rows 410 pixel rows 411 pixel rows 412 pixel rows 413 pixel rows 414 pixel rows 415 pixel rows Figure 5 501 Image Processing Device 502 filters Figure 6 600 Encoder 601 Image Processing Device 602 Filter Figure 7 700 decoder 701 Image Processing Device 702 Filter Figure 8 800 Block Edge Figure 9 1000 1st stage 1001 Second Stage 1002 Third Stage

[0149] Additional details of this disclosure are provided in Appendix A.

[0150] While several embodiments have been provided in this disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the disclosure. The examples should be considered illustrative and not limiting, and the intention should not be limited to the details given herein. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0151] Furthermore, in various embodiments, techniques, systems, subsystems, and methods described and shown separately or separately may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other elements shown and discussed as coupled to each other, directly coupled to each other, or in communication with each other may also be indirectly coupled or communicate through some interface, device, or intermediate component, whether electrical, mechanical, or otherwise. Other examples of modifications, substitutions, and alterations are ascertainable by those skilled in the art and may be made without departing from the spirit and scope disclosed herein. Provided below is a list of specific embodiments. Reference numbers in parentheses should be construed as exemplary and not limiting. Embodiment 1 An image processing device (501, 601, 701) for use in an image encoder (600) and / or an image decoder (700) for deblocking a block edge (403, 800) between a first coding block (401) and a second coding block (402) of an image encoded with a block code, the image processing device (501, 601, 701) comprising a filter (502, 602, 702) for filtering the block edge (403, 800), and for at least some of the pixels to be filtered within a deblocking range from the block edge (403, 800) and perpendicular to the block edge (403, 800): determining a filtered pixel value from the original pixel value and the at least one further pixel value of the pixel; determining a clipping value for a pixel depending on the pixel's distance from the block edge (403, 800); The pixel values to be filtered are clipped using the clipping value to obtain the resulting deblocked pixel values. It is configured as follows. Embodiment 2 2. The image processing device (501, 601, 701) of embodiment 1, wherein the clipping value is the maximum allowable change between the original pixel value and the deblocked pixel value. Embodiment 3 Clipping the pixel values to be filtered with the clipping value to result in deblocked pixel values is If the absolute value of the difference between the filtered pixel value and the deblocked pixel value does not exceed the clipping value of the pixel, setting the deblocked pixel value to the filtered pixel value; If the filtered pixel value exceeds the original pixel value plus the clipping value, setting the deblocked pixel value to the original pixel value plus the pixel's clipping value; If the filtered pixel value is less than the original pixel value minus the clipping value, set the deblocked pixel value to the original pixel value minus the pixel's clipping value. The image processing device (501, 601, 701) of embodiment 1 or 2, Embodiment 4 An image processing device (501, 601, 701) of any of embodiments 1 to 3, wherein the filter (502, 602, 702) is adapted to determine a clipping value of a pixel depending on the pixel's distance from the block edge (403, 800) by using a function or a lookup table. Embodiment 5 An image processing device (501, 601, 701) according to any one of embodiments 1 to 3, wherein the filter (502, 602, 702) is adapted to determine a clipping value of a pixel depending on the pixel's distance from the block edge (403, 800) by using a function that monotonically decreases as the pixel's distance from the block edge (403, 800) increases. Embodiment 6 6. The image processing device (501, 601, 701) of embodiment 5, wherein the function is an exponential function. Embodiment 7 The image processing device (501, 601, 701) of embodiment 6, wherein the function is tc'=tc+(tc>>i), where tc' is the clipping value, tc is a constant value, i is the pixel distance from the block edge (403, 800), and >> indicates a right shift. Embodiment 8 6. The image processing device (501, 601, 701) of embodiment 5, wherein the function is a linear function. Embodiment 9 The image processing device (501, 601, 701) of embodiment 8, wherein the function is tc'=tc+(tc-(i*x), where tc' is a clipping value, tc is a constant value, i is the distance of the pixel from the block edge (403, 800), and x is a constant value. Embodiment 10 In an image processing device (501, 601, 701) according to any one of embodiments 1 to 9, the filter (502, 602, 702) performs the following for each pixel to be filtered within a deblocking range from a block edge (403, 800) and perpendicular to the block edge (403, 800): The method is adapted to determine a filtered pixel value from the original pixel value of the pixel and at least one further pixel value, determine a clipping value for the pixel depending on the distance of the pixel from a block edge (403, 800), and clip the filtered pixel value using the clipping value to obtain a deblocked pixel value as a result. Embodiment 11 the filter (502, 602, 702) determines whether the block edge (403, 800) needs to be filtered based on the fact that, in the case of a vertical block edge (403, 800), the number of determined pixel columns is smaller than the number of pixel columns in the block surrounding the block edge (403, 800), and based on the fact that, in the case of a horizontal block edge (403, 800), the number of determined image rows is smaller than the number of pixel rows in the block surrounding the block edge (403, 800), and the filter (502, 602, 702) is adapted for each pixel to be filtered that is not in a determined pixel row or determined pixel column within a deblocking range from the block edge (403, 800) so that the deblocking range is perpendicular to the block edge (403, 800); determining a filtered pixel value from the original pixel value and the at least one further pixel value of the pixel; determining a clipping value for a pixel depending on the pixel's distance from a block edge (403, 800); clipping the pixel values to be filtered using the clipping value to result in deblocked pixel values; and The filter (502, 602, 702) performs the following for each pixel to be filtered in the determined pixel row or determined pixel column within the deblocking range from the block edge (403, 800) and perpendicular to the block edge (403, 800): determining a filtered pixel value from the original pixel value and the at least one further pixel value of the pixel; clipping the pixel values to be filtered using a constant clipping value to result in deblocked pixel values; 10. An image processing device (501, 601, 701) according to any one of embodiments 1 to 9, adapted to perform the following: Embodiment 12 12. The image processing device (501, 601, 701) of any of embodiments 1 to 11, wherein the filter (502, 602, 702) has a filter tap length of 1, or at least 2, or at least 3, or at least 4, or at least 5, or at least 6, or at least 7, or at least 8, or at least 9, or at least 10, or at least 11, or at least 12, or at least 13, or at least 14, or at least 15, or at least 16 pixels. Embodiment 13 An encoder for encoding an image, comprising an image processing device (501, 601, 701) of any of embodiments 1 to 12. Embodiment 14 A decoder for decoding an image, comprising an image processing device (501, 601, 701) of any of embodiments 1 to 12. Embodiment 15 A deblocking method for deblocking a block edge (403, 800) between a first coded block and a second coded block of an image encoded with a block code, the method comprising: for at least some of the pixels to be filtered within a deblocking range from the block edge (403, 800) and perpendicular to the block edge (403, 800), determining (1000) a filtered pixel value from an original pixel value of a pixel and at least one further pixel value; determining (1001) a clipping value for a pixel depending on the pixel's distance from a block edge (403, 800); The pixel values to be filtered are clipped using the clipping value to obtain the resulting deblocked pixel values (1002). A method for providing Embodiment 16 An encoding method for encoding an image, comprising the deblocking method of embodiment 15. Embodiment 17 A decoding method for decoding an image, comprising the deblocking method of embodiment 15. Embodiment 18 18. A computer program product comprising a program code for performing the method according to any of embodiments 15 to 17, when the computer program runs on a computer.

Claims

1. 1. An image processing device for use in an image encoder and / or image decoder for deblocking a block edge between a first block and a second block of an image, the image processing device comprising: at least one processor; one or more memories coupled to the at least one processor and storing programming instructions for execution by the at least one processor; the programming instructions causing the image processing device to: generating a filtered pixel value from original pixel values of a first pixel, a second pixel, and a third pixel, the second pixel and the third pixel being in the same determined pixel column and the first pixel being in a non-determined pixel column; clipping the filtered pixel values of the second pixel and the third pixel using a constant clipping value; clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from the block edge; An image processing device that performs the following:

2. The image processing device of claim 1 , wherein the distance of the second pixel from the block edge is different from the distance of the third pixel from the block edge.

3. Clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from the block edge comprises: The image processing device of claim 1 , further comprising obtaining the clipping value using a function or a look-up table.

4. 2. The image processing device of claim 1, wherein the clipping value of the first pixel is a monotonically decreasing function of the distance of the first pixel from the block edge.

5. 2. The image processing device of claim 1, wherein the first pixel, the second pixel, and the third pixel are within a deblocking range from the block edge, the deblocking range including a number of pixels in a line perpendicular to the block edge.

6. The at least one processor further executes the programming instructions to:

2. The image processing device of claim 1, wherein the filtered first pixel value is determined from the original first pixel value and at least one further pixel value of the first pixel.

7. The image processing device of claim 1 , wherein the decision pixel column is used to determine filtering to be performed.

8. 1. A deblocking method for deblocking a block edge between a first block and a second block of an image, comprising: generating filtered pixel values from original pixel values of a first pixel, a second pixel, and a third pixel, wherein the second pixel and the third pixel are in the same determined pixel column and the first pixel is in a non-determined pixel column; clipping the filtered pixel values of the second pixel and the third pixel using a constant clipping value; clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from the block edge; A method comprising:

9. The method of claim 8 , wherein the distance of the second pixel from the block edge is different from the distance of the third pixel from the block edge.

10. clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from the block edge, The method of claim 8 , comprising obtaining the clipping value using a function or a look-up table.

11. The method of claim 8 , wherein the clipping value of the first pixel is a monotonically decreasing function of the distance of the first pixel from the block edge.

12. 9. The method of claim 8, wherein the first pixel, the second pixel, and the third pixel are within a deblocking range from the block edge, the deblocking range including a number of pixels in a line that is perpendicular to the block edge.

13. The method described in claim 8, further comprising a step of determining the filtered first pixel value from the original first pixel value of the first pixel and at least one further pixel value.

14. The method of claim 8 , wherein the decision pixel column is used to determine filtering to be performed.

15. 1. A device for transmitting encoded data over a network, comprising: generating a filtered pixel value from original pixel values of a first pixel, a second pixel, and a third pixel, the second pixel and the third pixel being in the same determined pixel column and the first pixel being in a non-determined pixel column; clipping the filtered pixel values of the second pixel and the third pixel using a constant clipping value; clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from a block edge between a first block and a second block of an image; 11. A device comprising: an encoder configured to:

16. The device of claim 15 , wherein the distance of the second pixel from the block edge is different from the distance of the third pixel from the block edge.

17. Clipping the filtered pixel value of the first pixel with a clipping value that depends on the distance of the first pixel from the block edge comprises: The device of claim 15 , further comprising obtaining the clipping value using a function or a look-up table.

18. The device of claim 15 , wherein the clipping value of the first pixel is a monotonically decreasing function of the distance of the first pixel from the block edge.

19. 16. The device of claim 15, wherein the first pixel, the second pixel, and the third pixel are within a deblocking range from the block edge, the deblocking range including a number of pixels in a line that is perpendicular to the block edge.

20. The device of claim 15 , wherein the decision pixel column is used to determine filtering to be performed.

Images