Image encoding / decoding method and device, and recording medium on which bitstream is stored

Abstract

The present invention provides an image encoding method and an image decoding method. The image decoding method of the present invention may comprise the steps of: generating a prediction block of a current block; generating a reconstructed block of the current block on the basis of the prediction block; and filtering the reconstructed block on the basis of an in-loop filter, wherein the in-loop filter may include at least one of a cross-component sample offset (CCSO) or a constrained directional enhancement filter (CDEF).

Description

Video encoding / decoding method and device, and a recording medium storing a bitstream

[0001] The present invention relates to an encoder and a decoder, and more specifically, to a method and apparatus for encoding and decoding for generating a restored block of a current block.

[0002] Market demand for high-resolution video is increasing, and consequently, there is a need for technology that can efficiently compress high-resolution video. In response to these market demands, the Moving Picture Expert Group (MPEG) of ISO / IEC and the Video Coding Expert Group (VCEG) of ITU-T jointly formed the Joint Collaborative Team on Video Coding (JCT-VC), completed the development of the High Efficiency Video Coding (HEVC) video compression standard in January 2013, and have been actively conducting research and development on next-generation compression standards.

[0003] Techniques applied to video compression can broadly include intra-frame prediction (or intra prediction), inter-frame prediction (or inter prediction), transformation, quantization, entropy coding, and / or in-loop filters. Meanwhile, along with the increasing demand for high-resolution video, the demand for stereoscopic video content as a new video service is also increasing. Accordingly, there is active discussion regarding video compression technologies to effectively provide high-resolution and ultra-high-resolution stereoscopic video content.

[0004] The present disclosure aims to provide a method and apparatus for receiving an image input and performing in-loop filtering to generate a filtered image.

[0005] The present disclosure aims to provide an in-loop filtering method and apparatus for correcting sample values ​​within an image.

[0006] The present disclosure aims to provide a method and apparatus for deriving an offset of a current sample used to correct a current sample value.

[0007] The present disclosure aims to provide a method and apparatus for determining at least one surrounding sample to induce an offset of a current sample.

[0008] The present disclosure aims to provide a method and apparatus for classifying a current sample into a specific edge type in order to derive an offset of the current sample.

[0009] The present disclosure aims to provide a method and apparatus for classifying a current sample into a specific band type in order to induce an offset of the current sample.

[0010] The present disclosure aims to provide a method and apparatus for determining a color difference component sample at the same location as the current sample in order to derive an offset of the current sample, which is a luminance component.

[0011] The image decoding method and apparatus according to the present disclosure may generate a prediction block of a current block, generate a restoration block of the current block based on the prediction block, and filter the restoration block based on an in-loop filter. Here, the in-loop filter may include at least one of a Cross-Component Sample Offset (CCSO) and a Constrained Directional Enhancement Filter (CDEF).

[0012] In the image decoding method and apparatus according to the present disclosure, an offset of a current sample within the current block may be derived based on the CCSO. Here, the offset of the current sample may be for correcting the brightness value of the current sample.

[0013] In the image decoding method and apparatus according to the present disclosure, the offset may be derived based on a pre-defined table having at least one of the edge type, band type, or brightness value of the current sample as input.

[0014] In the image decoding method and apparatus according to the present disclosure, at least one of the edge type or band type of the current sample can be derived based on a reference sample of the current sample.

[0015] In the image decoding method and apparatus according to the present disclosure, the reference sample of the current sample may include a first reference sample. Here, the first reference sample may include at least one of a sample adjacent to the bottom, bottom-right, right, or top-right of the current sample; a sample located two rows down and one column to the right from the current sample; a sample located one row down and two columns to the right; a sample located one row up and two columns to the right; a sample located one row up and two columns to the right; or a sample located two rows up and one column to the right.

[0016] In the image decoding method and apparatus according to the present disclosure, the reference sample of the current sample may further include a second reference sample. Here, the second reference sample may include at least one of samples located along a predetermined direction from the first reference sample, and the predetermined direction may be determined based on the positional relationship between the first reference sample and the current sample.

[0017] In the image decoding method and apparatus according to the present disclosure, the reference sample of the current sample may be determined based on an index indicating the location of the reference sample.

[0018] In the image decoding method and apparatus according to the present disclosure, the reference sample of the current sample may include a reference sample at a position spaced apart from the current sample by a predetermined Manhattan distance. Here, the predetermined Manhattan distance may be determined based on a signaled index.

[0019] In the image decoding method and apparatus according to the present disclosure, the edge type of the current sample can be derived based on the result of comparing the brightness value of the current sample with the brightness value of the reference sample.

[0020] In the image decoding method and apparatus according to the present disclosure, the comparison result may be determined based on a reference value of the current block, and the reference value may be derived based on the characteristics of the current block. Here, the characteristics of the current block may mean at least one of a quantization rate, a brightness value, an average of the brightness values, a variance of the brightness values, a standard deviation of the brightness values, or a first or second derivative around the current sample.

[0021] In the image decoding method and apparatus according to the present disclosure, when the current sample is a luminance component sample, the characteristic of a block containing a chrominance component sample at the same location as the current sample may be used as the characteristic of the current block.

[0022] In the image decoding method and apparatus according to the present disclosure, when the current sample is a chrominance component sample, the characteristic of a block containing a luminance component sample at the same location as the current sample may be used as the characteristic of the current block.

[0023] The image encoding method and apparatus according to the present disclosure may generate a prediction block of a current block, generate a restoration block of the current block based on the prediction block, and filter the restoration block based on an in-loop filter. Here, the in-loop filter may include at least one of a Cross-Component Sample Offset (CCSO) or a Constrained Directional Enhancement Filter (CDEF).

[0024] A computer-readable storage medium according to the present disclosure can store a bitstream encoded by the image encoding method.

[0025] The bitstream transmission method and apparatus according to the present disclosure can transmit a bitstream generated by the image encoding method.

[0026] According to the present disclosure, by deriving the offset of the current sample within the current block based on the Cross-Component Sample Offset (CCSO), a more accurate prediction becomes possible, and thereby the compression performance of the encoder / decoder can be improved.

[0027] According to the present disclosure, by correcting the brightness value of the current sample based on the offset of the current sample, a more accurate prediction becomes possible, and thereby the compression performance of the encoder / decoder can be improved.

[0028] According to the present disclosure, by deriving the offset of the current sample based on the reference sample of the current sample, a more accurate prediction becomes possible, and thereby the compression performance of the encoder / decoder can be improved.

[0029] According to the present disclosure, by determining a reference sample of the current sample for deriving the offset of the current sample based on a signaled index, more efficient prediction becomes possible, and thereby the compression performance of the encoder / decoder can be improved.

[0030] FIG. 1 is a block diagram showing an image encoding device according to the present disclosure.

[0031] FIG. 2 is a block diagram showing an image decoding device according to the present disclosure.

[0032] FIG. 3 is a flowchart illustrating an image decoding method performed in an image decoding device according to the present disclosure.

[0033] FIG. 4 is a block diagram illustrating an embodiment of an in-loop filter that performs in-loop filtering according to the present disclosure.

[0034] FIG. 5 is a block diagram illustrating an embodiment of a Cross-Component Sample Offset (CCSO) according to the present disclosure.

[0035] FIG. 6 is a drawing illustrating an embodiment of a placement structure of a reference sample for deriving a current sample and an offset of the current sample according to the present disclosure.

[0036] FIG. 7 is a diagram showing the positional relationship between a luminance component sample and a color difference component sample according to the present disclosure.

[0037] Embodiments of the present invention are described in detail with reference to the drawings attached to this specification so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0038] Throughout this specification, when a part is described as being 'connected' to another part, this includes not only cases where they are directly connected, but also cases where they are electrically connected with other elements in between.

[0039] Furthermore, throughout this specification, when a part is described as 'comprising' a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0040] Additionally, terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0041] Additionally, in the embodiments relating to the device and method described herein, some components of the device or some steps of the method may be omitted. Also, the order of some components of the device or some steps of the method may be changed. Additionally, other components or other steps may be inserted into some components of the device or some steps of the method.

[0042] The components shown in the embodiments of the present invention are illustrated independently to represent different characteristic functions and do not imply that each component consists of separate hardware or a single software unit. That is, for convenience of explanation, each component is described as a separate component, and at least two of the components may be combined to form a single component, or a single component may be divided into multiple components to perform a function. Such integrated and separated embodiments of each component are also included within the scope of the present invention as long as they do not depart from the essence of the invention.

[0043] First, the terms used in this application are briefly explained as follows.

[0044] The video decoding apparatus described below may be a device included in a civilian security camera, civilian security system, military security camera, military security system, personal computer (PC), notebook computer, portable multimedia player (PMP), wireless communication terminal, smartphone, and server terminal such as a TV application server and service server; it may also refer to various devices equipped with a user terminal such as various devices, a communication device such as a communication modem for performing communication with a wired or wireless communication network, a memory for storing various programs and data for decoding video or predicting between or within a screen for decoding, and a microprocessor for executing programs to perform calculations and control.

[0045] In addition, the video encoded into a bitstream by the encoder can be transmitted to a video decoding device in real-time or non-real-time via wired or wireless communication networks such as the Internet, local area wireless communication networks, wireless LAN networks, WiBro networks, and mobile communication networks, or through various communication interfaces such as cables and Universal Serial Bus (USB), to be decoded, restored as a video, and played back. Alternatively, the bitstream generated by the encoder may be stored in memory. The memory may include both volatile and non-volatile memory. In this specification, memory may be described as a recording medium that stores the bitstream.

[0046] Typically, a video can be composed of a series of pictures, and each picture can be divided into coding units, such as blocks. Furthermore, those skilled in the art to which this embodiment belongs will understand that the term "picture" described below may be replaced with other terms having equivalent meanings, such as "image" or "frame." Additionally, those skilled in the art to which this embodiment belongs will understand that the term "coding unit" may be replaced with other terms having equivalent meanings, such as "unit block" or "block."

[0047] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings. In describing the present invention, redundant descriptions of identical components are omitted.

[0048] FIG. 1 is a block diagram showing an image encoding device according to the present invention. Referring to FIG. 1, a conventional image encoding device (100) may include a picture splitting unit (110), a prediction unit (120, 125), a conversion unit (130), a quantization unit (135), a reordering unit (160), an entropy encoding unit (165), an inverse quantization unit (140), an inverse conversion unit (145), a filter unit (150), and a memory (155).

[0049] The picture splitting unit (110) can split the input picture into at least one processing unit. At this time, the processing unit may be a Prediction Unit (PU), a Transform Unit (TU), or a Coding Unit (CU). In the following embodiments of the present invention, the term "coding unit" may be used to mean a unit that performs coding, or a unit that performs decoding.

[0050] A prediction unit may be divided into shapes such as at least one square or rectangle of the same size within a single encoding unit, or it may be divided such that one of the prediction units within a single encoding unit has a different shape and / or size from another prediction unit. When generating a prediction unit that performs intra prediction based on an encoding unit, if it is not the minimum encoding unit, intra prediction can be performed without dividing into multiple prediction units NxN.

[0051] The prediction unit (120, 125) may include an inter prediction unit (120) that performs inter prediction or inter-frame prediction, and an intra prediction unit (125) that performs intra prediction or intra-frame prediction. It may determine whether to use inter prediction or perform intra prediction for a prediction unit, and determine specific information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. The residual value (residual block) between the generated prediction block and the original block may be input to the conversion unit (130). In addition, the prediction mode information, motion vector information, etc. used for prediction may be encoded in the entropy encoding unit (165) along with the residual value and transmitted to the decoder. However, when the motion information derivation technique on the side of the decoder according to the present invention is applied, the prediction mode information, motion vector information, etc. are not generated in the encoder, so the information is not transmitted to the decoder. On the other hand, it is possible to signal and transmit from the encoder information instructing the derivation of motion information and information regarding the technique used to derive the motion information.

[0052] The inter prediction unit (120) may predict a prediction unit based on information of at least one picture among the previous picture or the subsequent picture of the current picture, and in some cases, may predict a prediction unit based on information of a partially encoded area within the current picture. The inter prediction unit (120) may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

[0053] In the reference picture interpolation unit, reference picture information is received from memory (155), and pixel information of integer pixels or less can be generated from the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter with different filter coefficients can be used to generate pixel information of integer pixels or less in 1 / 4 pixel units. In the case of chrominance signals, a DCT-based 4-tap interpolation filter with different filter coefficients can be used to generate pixel information of integer pixels or less in 1 / 8 pixel units.

[0054] The motion prediction unit can perform motion prediction based on a reference picture interpolated by the reference picture interpolation unit. Various methods such as FBMA (Full search-based Block Matching Algorithm), TSS (Three Step Search), and NTS (New Three-Step Search Algorithm) can be used to calculate motion vectors. Based on interpolated pixels, motion vectors can have motion vector values ​​in units of 1 / 2 or 1 / 4 pixels. The motion prediction unit can predict the current prediction unit by using different motion prediction methods. Various methods such as the Skip method, Merge method, AMVP (Advanced Motion Vector Prediction) method, and Intra Block Copy method can be used as motion prediction methods. In addition, when applying the motion information derivation technique on the side of the decoder according to the present invention, the methods performed by the motion prediction unit may include a template matching method and a bilateral matching method utilizing a motion trajectory.

[0055] The intra prediction unit (125) can generate a prediction unit based on reference pixel information around the current block, which is pixel information within the current picture. If the surrounding block of the current prediction unit is a block that has performed inter prediction, and the reference pixel is a pixel that has performed inter prediction, the reference pixel included in the block that has performed inter prediction can be replaced with the reference pixel information of the surrounding intra prediction block. That is, if the reference pixel is not available, the unavailable reference pixel information can be replaced with at least one of the available reference pixels.

[0056] Additionally, a residual block can be generated that includes residual value information, which is the difference between the prediction unit that performed the prediction based on the prediction unit generated in the prediction unit (120, 125) and the original block of the prediction unit. The generated residual block can be input to the conversion unit (130).

[0057] In the transformation unit (130), the residual block containing residual value information of the prediction unit generated through the original block and the prediction unit (120, 125) can be transformed using a transformation method such as DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), or KLT. Whether to apply DCT, DST, or KLT to transform the residual block can be determined based on the intra-prediction mode information of the prediction unit used to generate the residual block.

[0058] The quantization unit (135) can quantize the values ​​converted into the frequency domain in the conversion unit (130). The quantization coefficient may vary depending on the block or the importance of the image. The values ​​produced by the quantization unit (135) may be provided to the inverse quantization unit (140) and the reordering unit (160).

[0059] The reordering unit (160) can perform reordering of coefficient values ​​for quantized residual values.

[0060] The reordering unit (160) can convert two-dimensional block-shaped coefficients into one-dimensional vector forms through a coefficient scanning method. For example, the reordering unit (160) can convert the coefficients from DC to high-frequency range coefficients into one-dimensional vector forms by scanning using a Zig-Zag Scan method. Depending on the size of the conversion unit and the intra-prediction mode, a vertical scan that scans two-dimensional block-shaped coefficients in the column direction or a horizontal scan that scans two-dimensional block-shaped coefficients in the row direction may be used instead of the Zig-Zag Scan. That is, depending on the size of the conversion unit and the intra-prediction mode, it can be determined whether to use a Zig-Zag Scan, a vertical scan, or a horizontal scan.

[0061] The entropy encoding unit (165) can perform entropy encoding based on the values ​​calculated by the reordering unit (160). Entropy encoding can use various encoding methods, such as, for example, Exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding). In this regard, the entropy encoding unit (165) can encode residual value coefficient information of the encoding unit from the reordering unit (160) and the prediction unit (120, 125). Additionally, according to the present invention, it is possible to signal and transmit information indicating that motion information is derived and used in the decoder side, and information regarding the technique used for deriving motion information.

[0062] In the inverse quantization unit (140) and inverse transformation unit (145), the values ​​quantized in the quantization unit (135) are inverse quantized, and the values ​​transformed in the transformation unit (130) are inverse transformed. The residual value generated in the inverse quantization unit (140) and inverse transformation unit (145) can be combined with the prediction unit predicted through the motion estimation unit, motion compensation unit, and intra prediction unit included in the prediction unit (120, 125) to generate a reconstructed block.

[0063] The filter unit (150) may include at least one of a deblocking filter, an offset correction unit, and an Adaptive Loop Filter (ALF). The deblocking filter can remove block distortion caused by boundaries between blocks in the restored picture. The offset correction unit can correct the offset from the original image on a pixel-by-pixel basis for the image that has undergone deblocking. To perform offset correction for a specific picture, a method may be used in which pixels included in the image are divided into a certain number of regions, the region to be offset is determined, and the offset is applied to that region, or a method may be used in which the offset is applied by considering the edge information of each pixel. Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered restored image with the original image. After dividing the pixels included in the image into a predetermined group, a filter to be applied to that group is determined, and filtering may be performed differentially for each group.

[0064] The memory (155) can store a restored block or picture produced through the filter unit (150), and the stored restored block or picture can be provided to the prediction unit (120, 125) when performing inter-prediction.

[0065] FIG. 2 is a block diagram showing an image decoding device according to the present invention. Referring to FIG. 2, the image decoder (200) may include an entropy decoding unit (210), a reordering unit (215), an inverse quantization unit (220), an inverse transformation unit (225), a prediction unit (230, 235), a filter unit (240), and a memory (245).

[0066] When a video bitstream is input to a video encoder, the input bitstream can be decoded using the reverse procedure of the video encoder.

[0067] The entropy decoding unit (210) can perform entropy decoding in the opposite procedure to that which the entropy encoding unit of the image encoder performed. For example, various methods such as Exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding) can be applied in correspondence with the method performed in the image encoder.

[0068] The entropy decoding unit (210) can decode information related to intra-prediction and inter-prediction performed in the encoder.

[0069] The reordering unit (215) can perform reordering based on the method of reordering the entropy-decoded bitstream in the encoding unit in the entropy decoding unit (210). The coefficients expressed in the form of a one-dimensional vector can be reordered by restoring them to the form of two-dimensional block coefficients.

[0070] The inverse quantization unit (220) can perform inverse quantization based on the coefficient values ​​of the rearranged block and the quantization parameters provided by the encoder.

[0071] The inverse transform unit (225) can perform inverse transforms, i.e., inverse DCT, inverse DST, and inverse KLT, on the transforms, i.e., DCT, DST, and KLT, performed by the transform unit on the quantization result performed by the image encoder. The inverse transform can be performed based on the transmission unit determined by the image encoder. In the inverse transform unit (225) of the image decoder, a transformation technique (e.g., DCT, DST, KLT) can be selectively performed according to multiple pieces of information such as a prediction method, the size of the current block, and the prediction direction.

[0072] The prediction unit (230, 235) can generate a prediction block based on the prediction block generation information provided by the entropy decoding unit (210) and the previously decoded block or picture information provided by the memory (245).

[0073] As described above, when performing intra prediction or intra-frame prediction identical to the operation in the video encoder, if the size of the prediction unit and the size of the transform unit are the same, intra prediction for the prediction unit is performed based on the pixels to the left of the prediction unit, the pixels to the top left, and the pixels to the top; however, if the size of the prediction unit and the size of the transform unit are different when performing intra prediction, intra prediction can be performed using reference pixels based on the transform unit. Additionally, intra prediction using NxN partitioning only for the minimum encoding unit may also be used.

[0074] The prediction unit (230, 235) may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives various information, such as prediction unit information input from the entropy decoding unit (210), prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, distinguishes the prediction unit in the current encoding unit, and determines whether the prediction unit performs inter prediction or intra prediction. On the other hand, if the encoder (100) does not transmit motion prediction related information for the inter prediction, but instead transmits information indicating that motion information is derived and used from the decoder side and information regarding the technique used for deriving motion information, the prediction unit determination unit determines whether the inter prediction unit (23) performs prediction based on the information transmitted from the encoder (100).

[0075] The inter prediction unit (230) can perform inter prediction for the current prediction unit based on information included in at least one picture, either a previous picture or a subsequent picture, of the current picture containing the current prediction unit, using information required for inter prediction of the current prediction unit provided by the video encoder. To perform inter prediction, it can determine whether the motion prediction method of the prediction unit included in the corresponding encoding unit is a Skip Mode, Merge Mode, AMVP Mode, or Intra Block Copy Mode based on the encoding unit. Alternatively, the inter prediction unit (230) can perform inter prediction by inducing motion information itself from information provided by the video encoder indicating that motion information is to be induced and used from the decoder side and information regarding the technique used to induce motion information.

[0076] The intra prediction unit (235) can generate a prediction block based on pixel information within the current picture. If the prediction unit is a prediction unit that has performed intra prediction, it can perform intra prediction based on the intra prediction mode information of the prediction unit provided by the image encoder. The intra prediction unit (235) may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a part that performs filtering on the reference pixel of the current block, and can determine whether to apply the filter based on the prediction mode of the current prediction unit. AIS filtering can be performed on the reference pixel of the current block using the prediction mode of the prediction unit and the AIS filter information provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

[0077] The reference pixel interpolation unit can generate a reference pixel of an integer value or less by interpolating the reference pixel when the prediction mode of the prediction unit is a prediction unit that performs intra-prediction based on the pixel value interpolated from the reference pixel. If the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is DC mode.

[0078] The restored block or picture may be provided to a filter unit (240). The filter unit (240) may include a deblocking filter, an offset correction unit, and an ALF.

[0079] Information regarding whether a deblocking filter has been applied to the corresponding block or picture can be received from the video encoder, and if a deblocking filter has been applied, information regarding whether a strong filter or a weak filter has been applied. The deblocking filter of the video decoder receives information related to the deblocking filter provided by the video encoder and can perform deblocking filtering on the corresponding block.

[0080] The offset correction unit can perform offset correction on the restored image based on the type of offset correction and offset value information applied to the image during encoding. ALF can be applied to the encoding unit based on information on whether ALF is applied and ALF coefficient information provided by the encoder. This ALF information can be provided included in a specific parameter set.

[0081] The memory (245) can store the restored picture or block so that it can be used as a reference picture or reference block, and can also provide the restored picture to the output unit.

[0082] FIG. 3 is a flowchart illustrating an image decoding method performed in an image decoding device according to the present disclosure.

[0083] Referring to FIG. 3, a prediction block of the current block can be generated (S300). For example, the prediction block of the current block can be generated based on an intra prediction method or an inter prediction method.

[0084] Referring to FIG. 3, a restoration block of the current block can be generated based on a prediction block of the current block (S310). For example, the current block can be restored based on at least one of a prediction block of the current block or a residual block of the current block.

[0085] Referring to FIG. 3, the restoration block of the current block can be filtered based on an in-loop filter (S320). The filtering based on the in-loop filter will be examined in detail with reference to FIG. 4 to 7.

[0086] FIG. 4 is a block diagram illustrating an embodiment of an in-loop filter that performs in-loop filtering according to the present disclosure.

[0087] Referring to FIG. 4, the in-loop filter may include at least one of a deblocking filter (410), a CCSO (Cross-Component Sample Offset) (420), a CDEF (Constrained Directional Enhancement Filter) (430), a super-resolution filter (440), or a loop restoration filter (450).

[0088] The above-mentioned in-loop filter may apply a deblocking filter to the input image. Additionally, at least one of CCSO or CDEF may be applied to the image to which the deblocking filter has been applied. In this case, a filtered image may be generated based on at least one of the image to which CCSO has been applied or the image to which CDEF has been applied. Furthermore, a super-resolution filter may be applied to the filtered image to generate an image with a changed resolution. Additionally, a loop restoration filter may be applied to the image with the changed resolution.

[0089] A deblocking filter (410) can receive an image and modify the values ​​of samples located at the boundaries of blocks to remove block artifacts. More specifically, the deblocking filter calculates the difference between the sample values ​​located at the boundary of the current block and the sample values ​​located at the boundary of an adjacent block, and if the difference is below a predetermined threshold, it can mitigate the discontinuity of the block boundaries by modifying the values ​​of the samples located at the boundaries. Conversely, if the difference between the sample values ​​exceeds the threshold, it is highly likely that the boundary is an object boundary within the actual image, so the degree of modification of the boundary sample values ​​may be limited or no modification may be performed. Through this, the deblocking filter can provide the effect of preserving the actual edges of the image while reducing blocking artifacts caused by block-based encoding.

[0090] The CCSO (Cross-Component Sample Offset) (420) receives an image and can derive an offset for the sample to correct the brightness value of the sample within the current block. More specifically, the CCSO can calculate an offset corresponding to the current sample by using a chrominance component sample at the same location when the current sample is a luminance component, and by using a luminance component sample at the same location when the current sample is a chrominance component. Additionally, the CCSO can classify the current sample into a specific band type or edge type. The current sample value can be corrected by deriving an offset based on at least one of the classification result or the sample value of the correlation component of the current sample (e.g., the chrominance component when the current sample is a luminance component). Through this, the CCSO can reduce chrominance distortion or ringing artifacts within the image and improve the overall image quality.

[0091] A CDEF (Constrained Directional Enhancement Filter) (430) can modify the values ​​of samples by receiving an image input and performing filtering while preserving the directionality to enhance the directionality. More specifically, the CDEF can determine the local directionality by analyzing the area surrounding the current sample within the current block and modify the sample values ​​by applying a correction filter within a limited range along the directionality. Accordingly, the CDEF can provide the effect of improving visual quality while preserving the structural characteristics of the image.

[0092] The super-resolution filter (440) can receive an image and change its resolution. More specifically, the super-resolution filter can increase or decrease the spatial resolution by interpolating or resampling samples of the input image, and can perform filtering to minimize boundary distortion or ringing artifacts in the process. Accordingly, the super-resolution filter can provide the effect of providing a high-resolution output image even after decoding an image encoded at a low resolution.

[0093] A loop restoration filter (450) can receive an image as input and output a restored image using a filter. More specifically, the loop restoration filter can suppress noise generated during the encoding and decoding process and preserve the detailed structure of the image by applying a higher-order filter, such as a Wiener filter or a self-guided filter, to specific block units of the image.

[0094] The above process of applying multiple filters may be performed differently from the order shown in FIG. 4, and some or all of them may be omitted. For example, a deblocking filter may be applied after CCSO is applied to the input image, or only CCSO may be applied to the input image.

[0095] FIG. 5 is a block diagram illustrating an embodiment of a Cross-Component Sample Offset (CCSO) according to the present disclosure.

[0096] Referring to FIG. 5, the CCSO (Cross-Component Sample Offset) may include at least one of a sample determination unit (510), an edge classification unit (520), a band classification unit (530), or an offset induction unit (540). The CCSO can induce an offset for each sample and correct the brightness value of the sample in the image based on the induced offset.

[0097] The sample determination unit (510) of FIG. 5 can determine a reference sample to be referenced in order to derive an offset for correcting the brightness value of the current sample. Here, the determined reference sample may mean a single reference sample or a plurality of reference samples. The reference sample may be determined based on a certain unit standard. For example, the reference sample may be determined in frame units or CTU (Coding Tree Unit) units. As another example, the reference sample may be determined in pre-defined units for CCSO. The pre-defined unit may be a 128x128 block unit.

[0098] Hereinafter, we will examine the sample determination unit (510) in detail with reference to FIG. 6.

[0099] FIG. 6 is a drawing illustrating an embodiment of a placement structure of a reference sample for deriving a current sample and an offset of the current sample according to the present disclosure.

[0100] Referring to FIG. 6, the offset for the current sample (S) used for CCSO application may be derived based on one or more reference samples. The reference samples may include at least one of a first reference sample or a second reference sample. For example, the first reference sample may include at least one of a sample adjacent to the bottom of the current sample (sample a in FIG. 6), a sample adjacent to the bottom right of the current sample (sample b in FIG. 6), a sample adjacent to the right of the current sample (sample c in FIG. 6), a sample adjacent to the top right of the current sample (sample d in FIG. 6), a sample at a position 2 rows down and 1 column to the right from the current sample (sample e in FIG. 6), a sample at a position 1 row down and 2 columns to the right from the current sample (sample f in FIG. 6), a sample at a position 1 row up and 2 columns to the right from the current sample (sample g in FIG. 6), or a sample at a position 2 rows up and 1 column to the right from the current sample (sample h in FIG. 6).

[0101] The second reference sample may include a sample located along a predetermined direction from the first reference sample. Here, the predetermined direction may be determined based on the positional relationship between the first reference sample and the current sample. For example, the second reference sample may include a sample located at a predetermined distance in the direction in which the first reference sample is located on an extension line connecting the current sample and the first reference sample. Here, the sample located at the predetermined distance may refer to a sample located at a distance of 0 to 4 samples from the first reference sample, and the sample located at a distance of 0 samples may refer to the first reference sample itself. For example, among the samples on the extension line of sample a of FIG. 6 and the current sample, a sample at a distance of 2 samples from sample a of FIG. 6 (sample i of FIG. 6) or a sample at a distance of 4 samples (sample k of FIG. 6) in the direction in which sample a of FIG. 6 is located may be included in the second reference sample. Alternatively, among the samples on the extension line of sample c of FIG. 6 and the current sample, a sample at a distance of 1 sample from sample c of FIG. 6, a sample at a distance of 2 samples (sample j of FIG. 6), or a sample at a distance of 4 samples (sample l of FIG. 6) may be included in the second reference sample in the direction where sample c of FIG. 6 is located.

[0102] Since the location of the reference sample shown in FIG. 6 is merely one example of a reference sample placement structure for inducing an offset of the current sample (S), other reference samples other than the location shown in FIG. 6 may be used.

[0103] The sample determination unit (510) can determine a reference sample based on a signaled index. At this time, a single reference sample or multiple reference samples may be selected depending on the value of the signaled index. For example, a single reference sample (R1) at a location corresponding to the value of the signaled index may be selected. In this case, based on the distance between the current sample and the reference sample (R1), another reference sample (L1) located at a position in the opposite direction, separated by the same distance as the distance on the extension line connecting the current sample and the reference sample (R1), may be additionally selected.

[0104] As another example, after a sample at a location corresponding to the value of a signaled index is selected, a reference sample (A1) of the current sample may be determined based on the value of the signaled index and the location of the selected sample. For example, a sample located at a distance corresponding to the value of the signaled index in the direction where the selected sample is located on an extension line connecting the selected sample and the current sample may be determined as the reference sample (A1) of the current sample. Here, the distance may be greater than or equal to 0 sample distance. In this case, another reference sample (B1) located at a position in the opposite direction, at a distance equal to the distance between the current sample and the reference sample (A1) on the extension line connecting the current sample and the reference sample (A1), may be additionally selected.

[0105] As another example, multiple reference samples (R2, R3) corresponding to a predefined pair of positions may be selected based on the value of the signaled index. In this case, based on the distance between the current sample and the center point of the multiple reference samples (R2, R3), additional multiple reference samples (L2, L3) may be selected, located in the opposite direction at a distance equal to the distance on the extension line connecting the current sample and the center point.

[0106] As another example, one or more reference samples located at a specific distance from the current sample may be selected based on the value of the signaled index. In this case, the distance may refer to the Manhattan distance, which can be calculated by finding the absolute values ​​of the horizontal distance difference and the vertical distance difference between the reference point of the current sample and the reference point of the reference sample, respectively, and then summing them.

[0107] As another example, a reference sample located at a distance corresponding to the value of the signaled index may be selected from a reference sample surrounding the current sample selected based on the value of the signaled index. For example, a sample located at a distance of 1 corresponding to the value of the signaled index may be selected as a reference sample to induce an offset of the current sample (S), centered on a reference sample adjacent to the right of the current sample selected based on the value of the signaled index (sample c in FIG. 6).

[0108] An index for selecting reference samples may be signaled as a value within a specific range, and one or more reference samples may be selected according to the value of the signaled index. For example, the index may have a first value through an eighth value, and a reference sample at a corresponding position may be selected according to the value of the signaled index. For example, if the value of the index is signaled as a first value, a second value, a third value, a fourth value, a fifth value, a sixth value, a seventh value, or an eighth value, reference samples a, b, c, d, e, f, g, or h of FIG. 6 may be selected, respectively. Alternatively, a reference sample adjacent to the right of reference sample c of FIG. 6 may be selected based on the value of the index instead of any one of the reference samples a through h. Additionally, as described above, another reference sample located at a symmetrical position relative to the current sample and the reference sample selected according to the value of the index may be additionally selected.

[0109] As another example, the index may have values ​​from the first to the sixth value. In this case, a reference sample at a corresponding position may be selected according to the value of the signaled index, or multiple reference samples corresponding to a predefined pair of positions may be selected. For example, when the index value is signaled as the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, or twelfth value, reference samples a, b, c, d, e, f, g, h, i, j, k, or l of FIG. 6 may be selected, respectively. Alternatively, a reference sample adjacent to the right of reference sample c of FIG. 6 may be selected based on the value of the index instead of any one of the reference samples a through l. Additionally, when the value of the index is signaled as the 13th value, 14th value, 15th value, or 16th value, a pair of reference samples (b, e), (b, f), (d, g), or (d, h) of FIG. 6, respectively, may be selected. Additionally, as described above, an additional reference sample located symmetrically to the current sample and the reference sample selected according to the value of the index may be selected.

[0110] As another example, the index may have values ​​from a first value to a third value, and one or more reference samples located at a distance corresponding to the value of the signaled index may be selected. For example, when the value of the index is signaled as a first value, a second value, or a third value, reference samples with a Manhattan distance of 1, 2, or 3 from the current sample may be selected, respectively.

[0111] The edge classification unit (520) of FIG. 5 can classify the current sample into a specific edge type based on a reference sample determined by the sample determination unit (510). More specifically, the edge classification unit (520) can determine the edge type of the current sample based on the relationship between the brightness value of the reference sample and the brightness value of the current sample. At this time, the value obtained by adding a reference value (T) to the brightness value of the current sample can be called the first value, and the value obtained by subtracting the reference value (T) from the brightness value of the current sample can be called the second value.

[0112] For example, the edge classification unit (520) can classify the edge type of the current sample into one of four edge types. For example, the edge type of the current sample can be classified according to whether the brightness value of the reference sample determined by the sample determination unit (510) is greater than or equal to the first value, is less than the first value and is greater than or equal to the brightness value of the current sample, is less than the brightness value of the current sample and is greater than or equal to the second value, or is less than the second value.

[0113] As another example, the edge classification unit (520) can classify the edge type of the current sample into one of 16 edge types. For example, the edge type of the current sample can be derived based on the brightness values ​​of a plurality of reference samples (A1, A2) selected by the sample determination unit (510). More specifically, A1 and A2 can each be divided into 4 classifications based on the relationship of brightness values ​​with the current sample, and the edge type of the current sample can be classified into one of 16 types depending on the classification combination of A1 and A2 (i.e., 4 x 4 = 16).

[0114] As another example, the edge classification unit (520) can classify the edge type of the current sample into one of three edge types. For example, the edge type of the current sample can be classified according to whether the brightness value of the reference sample determined by the sample determination unit (510) is greater than or equal to the brightness value of the current sample, whether it is less than the brightness value of the current sample and greater than or equal to the second value, or whether it is less than the second value.

[0115] As another example, the edge classification unit (520) can classify the edge type of the current sample into one of nine edge types. For example, the edge type of the current sample can be derived based on the brightness values ​​of a plurality of reference samples (B1, B2) selected by the sample determination unit (510). More specifically, B1 and B2 can each be divided into three classifications based on the relationship of brightness values ​​with the current sample, and the edge type of the current sample can be classified into one of nine types depending on the classification combination of B1 and B2 (i.e., 3 x 3 = 9).

[0116] The reference value (T) used to derive the edge type of the current sample may be set to different values ​​depending on the embodiment. For example, the reference value (T) may be determined by referring to a pre-defined table in the decoder based on an index signaled in the encoder.

[0117] As another example, a reference value (T) can be derived based on the characteristics of the current block containing the current sample. In this case, the characteristics of the current block may be at least one of the quantization rate, brightness value, mean of brightness value, variance of brightness value, standard deviation of brightness value, or first or second derivative values ​​around the current sample. Additionally, if the current sample is a luminance component sample, the characteristics of the chrominance component block may be used, and if the current sample is a chrominance component sample, the characteristics of the luminance component block may be used. If the current sample is a luminance component sample or a chrominance component sample, the chrominance component block or luminance component block used to derive the reference value may refer to a block containing a component sample different from the current sample at the same location as the current sample. The component sample different from the current sample at the same location as the current sample will be explained in detail with reference to FIG. 7.

[0118] FIG. 7 is a diagram showing the positional relationship between a luminance component sample and a color difference component sample according to the present disclosure.

[0119] Referring to FIG. 7, the positions corresponding to 1, 2, 3, and 4 may each represent the positions of luminance component samples, and a color difference component sample at the same position as the luminance component sample may exist in at least one of the positions corresponding to 1 to 9 in FIG. 7. For example, the color difference component sample at the same position as the luminance component sample may be located in at least one of the positions corresponding to 1 or 6 in FIG. 7.

[0120] As another example, the location of the chrominance component sample at the same location as the current sample, which is the luminance component, can be determined based on the image format. For example, the location of the chrominance component sample can be determined as corresponding to 6 in Fig. 7 if the image format is YUV 4:2:0, 5 in Fig. 7 if the image format is YUV 4:2:2, and 1 in Fig. 7 if the image format is RGB 4:4:4.

[0121] The edge type of the current sample classified by the edge classification unit (520) of FIG. 5 can be transmitted to the offset induction unit (540) of FIG. 5, and the offset induction unit can induce an offset of the current sample based on the edge type of the current sample.

[0122] The band classification unit (530) of FIG. 5 can classify the current sample into a specific band type based on at least one of the reference sample or the current sample determined by the sample determination unit (510). More specifically, the band classification unit (530) can determine the band type of the current sample by dividing the range of the total brightness value (e.g., 0 to 255) into a plurality of consecutive intervals and determining the interval containing the brightness value derived based on at least one of the reference sample or the current sample.

[0123] For example, the band classification unit (530) can determine which range the brightness value derived based on the reference sample and the current sample determined by the sample determination unit (510) belongs to, thereby deriving the band type of the current sample. As another example, the band classification unit may derive the band type of the current sample using the brightness value derived based on the reference sample determined by the sample determination unit. As yet another example, the band classification unit may determine which range the brightness value of the current sample belongs to, thereby deriving the band type of the current sample. Here, the derived brightness value used to derive the band type of the current sample may be calculated based on at least one of the average of the brightness values, the median of the brightness values, the maximum of the brightness values, the minimum of the brightness values, or the first or second derivative between the samples. Additionally, the reference sample may be a single reference sample or a plurality of reference samples.

[0124] The method for determining the number of intervals into which the range of total brightness values ​​(e.g., 0 to 255) is divided may vary depending on the embodiment. For example, information regarding the number of interval divisions may be included in the bitstream and signaled from the encoder. For another example, the number of interval divisions may be determined based on the characteristics of the current block containing the current sample. In this case, the characteristics may refer to at least one of the first or second derivative value, brightness value, average of brightness value, variance of brightness value, or standard deviation of brightness value within the current block. For example, if the second derivative value of the samples within the current block is greater than a predetermined value, the range of total brightness values ​​may be divided into more intervals (i.e., finer). Alternatively, if the variance of the brightness values ​​of the samples within the current block is greater than a predetermined value, the range of total brightness values ​​may be divided into more intervals.

[0125] The range of the total brightness values ​​(e.g., 0 to 255) may be divided evenly or unevenly. That is, the divided intervals may all be of the same range (e.g., if divided into 4 intervals, 0-63, 64-127, 128-191, 192-255), and the ranges of the divided intervals may be different.

[0126] When the range of the total brightness values ​​is divided unevenly, the information related to the segment division may be derived differently depending on the embodiment. For example, the information related to the segment division may be derived based on the characteristics of the current block containing the current sample. In this case, the characteristics may mean at least one of the first or second derivative within the current block, the brightness value, the average of the brightness values, the variance of the brightness values, or the standard deviation of the brightness values.

[0127] For example, if the average of the brightness values ​​within the current block is greater than a predetermined value, the range of brightness values ​​within the total range can be divided more finely (i.e., the interval length can be relatively short) for sections with relatively high brightness values, and the range of brightness values ​​within the total range can be divided more long for sections with relatively low brightness values. Alternatively, if the variance of the brightness values ​​within the current block is smaller than a predetermined value, the range of brightness values ​​within the total range can be divided more finely (i.e., the interval length can be relatively short) for sections around the average of the brightness values ​​within the current block, and the remaining sections can be divided more long for sections.

[0128] If the current sample is a luminance component sample, the characteristics of the chrominance component block may be used as the characteristics of the current block, and if the current sample is a chrominance component sample, the characteristics of the luminance component block may be used as the characteristics of the current block. More specifically, if the current sample is a luminance component sample, the characteristics of the block containing the chrominance component sample at the same location as the current sample may be used as the characteristics of the current block, and if the current sample is a chrominance component sample, the characteristics of the block containing the luminance component sample at the same location as the current sample may be used. As the component samples different from the current sample at the same location as the current sample have been described above with reference to FIG. 7, a redundant description is omitted.

[0129] As another example, information related to segment division can be derived based on pre-defined range information in the decoder. As yet another example, the information related to segment division can be derived based on a bitstream signaled by the encoder. In this case, the bitstream may indicate which of the multiple pre-defined range information in the decoder is used. Alternatively, the bitstream may include at least one of information regarding the length of each segment being divided or information regarding the range where finer division is performed.

[0130] The band type of the current sample classified in the band classification unit (530) of FIG. 5 can be transmitted to the offset induction unit (540) of FIG. 5, and the offset induction unit can induce an offset of the current sample based on the band type of the current sample.

[0131] The offset induction unit (540) of FIG. 5 can induce an offset of the current sample based on offset induction information. For example, the offset induction unit (540) can induce an offset of the current sample by referring to a table pre-defined in the decoder based on offset induction information. Here, the offset induction information may include at least one of the edge type of the current sample classified by the edge classification unit (520), the band type of the current sample classified by the band classification unit (530), or the brightness value of the current sample. For example, the offset induction unit can induce an offset of the current sample by referring to a table pre-defined in the decoder based on the edge type of the current sample and the band type of the current sample, which are offset induction information.

[0132] For example, the offset induction unit (540) may derive the offset of the current sample by referring to a pre-defined table in the decoder based on the edge type of the current sample classified by the edge classification unit. As another example, the offset induction unit may derive the offset by referring to a pre-defined table in the decoder based on the edge type and brightness value of the current sample. As yet another example, the offset induction unit may derive the offset of the current sample by referring to a pre-defined table in the decoder based on the band type of the current sample classified by the band classification unit. Alternatively, the offset induction unit may derive the offset of the current sample by referring to a pre-defined table in the decoder based on the band type and brightness value of the current sample.

[0133] As another example, the offset derivation unit can derive the offset of the current sample by referring to a pre-defined table in the decoder based on the combination of the edge type and band type of the current sample and the brightness value of the current sample. As another example, the offset derivation unit can derive the offset of the current sample by referring to a pre-defined table in the decoder based on the combination of the edge type and band type of the current sample.

[0134] The offset of the current sample derived from the offset induction unit can be used to correct the brightness value of the current sample. Alternatively, it may be used as an input to the super-resolution filter (440) or loop restoration filter (450) of FIG. 4, either together with the output of the CDEF (430) of FIG. 4 or alone.

[0135] As previously described with reference to FIGS. 3 to 7, the encoding method and apparatus according to the present disclosure may generate a prediction block of a current block, generate a restoration block based on the prediction block, and filter the restoration block through an in-loop filter. Here, the in-loop filter may include at least one of a deblocking filter, a CCSO (Cross-Component Sample Offset), a CDEF (Constrained Directional Enhancement Filter), a super-resolution filter, or a loop restoration filter. Additionally, the CCSO may determine a reference sample of a current sample within the current block to derive an offset for correcting the current block, and derive an edge type or band type of the current sample based on the reference sample. Additionally, the brightness value of the current sample may be corrected based on the derived offset.

[0136] The various embodiments of the present disclosure are not intended to list all possible combinations but to describe representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more.

[0137] In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of implementation by hardware, it may be implemented by one or more ASICs (Application Specific Integrated Circuits), DSPs (Digital Signal Processors), DSPDs (Digital Signal Processing Devices), PLDs (Programmable Logic Devices), FPGAs (Field Programmable Gate Arrays), general processors, controllers, microcontrollers, microprocessors, etc.

[0138] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating system, application, firmware, program, etc.) that enable an operation according to a method of various embodiments to be executed on a device or computer, and a non-transitory computer-readable medium on which such software or instructions, etc. are stored and executable on a device or computer.

[0139] The present disclosure may be used industrially in the field of methods, devices, and recording media for image encoding / decoding.

Claims

1. A step of generating a predicted block of the current block; A step of generating a restoration block of the current block based on the prediction block; and The method includes the step of filtering the restoration block based on an in-loop filter, An image decoding method in which the above-mentioned in-loop filter comprises at least one of CCSO (Cross-Component Sample Offset) or CDEF (Constrained Directional Enhancement Filter).

2. In Paragraph 1, Based on the above CCSO, the offset of the current sample within the above current block is derived, and An image decoding method in which the offset of the current sample is for correcting the brightness value of the current sample.

3. In Paragraph 2, An image decoding method in which the above offset is derived based on a pre-defined table that takes at least one of the edge type, band type, or brightness value of the current sample as input.

4. In Paragraph 3, An image decoding method in which at least one of the edge type or band type of the current sample is derived based on a reference sample of the current sample.

5. In Paragraph 4, The reference sample of the above current sample includes a first reference sample, and A video decoding method comprising at least one of the following: the first reference sample includes a sample adjacent to the bottom, bottom-right, right, or top-right of the current sample; a sample located 2 rows down and 1 column to the right from the current sample; a sample located 1 row down and 2 columns to the right; a sample located 1 row up and 2 columns to the right; or a sample located 2 rows up and 1 column to the right.

6. In Paragraph 5, The reference sample of the above current sample further includes a second reference sample, and The second reference sample comprises at least one of the samples located along a predetermined direction from the first reference sample, and An image decoding method in which the above predetermined direction is determined based on the positional relationship between the first reference sample and the current sample.

7. In Paragraph 6, An image decoding method in which the reference sample of the current sample is determined based on an index indicating the location of the reference sample.

8. In Paragraph 4, The reference sample of the above current sample includes a reference sample at a location spaced apart from the above current sample by a predetermined Manhattan distance, and An image decoding method in which the above-mentioned predetermined Manhattan distance is determined based on a signaled index.

9. In Paragraph 4, An image decoding method in which the edge type of the current sample is derived based on the result of comparing the brightness value of the current sample and the brightness value of the reference sample.

10. In Paragraph 9, The above comparison result is determined based on the reference value of the current block, and The above reference value is derived based on the characteristics of the current block, and An image decoding method wherein the characteristics of the current block above mean at least one of a quantization rate, a brightness value, an average of the brightness values, a variance of the brightness values, a standard deviation of the brightness values, or a first or second derivative around the current sample.

11. In Paragraph 10, A video decoding method in which, when the current sample is a luminance component sample, the characteristics of a block containing a chrominance component sample at the same location as the current sample are used as the characteristics of the current block.

12. In Paragraph 10, A video decoding method in which, when the current sample is a color difference component sample, the characteristics of a block containing a luminance component sample at the same location as the current sample are used as the characteristics of the current block.

13. Step of generating a predicted block of the current block; A step of generating a restoration block of the current block based on the prediction block; and The method includes the step of filtering the restoration block based on an in-loop filter, An image encoding method wherein the above-mentioned in-loop filter comprises at least one of CCSO (Cross-Component Sample Offset) or CDEF (Constrained Directional Enhancement Filter).

14. A non-transient computer-readable storage medium for storing a bitstream generated by the image encoding method according to paragraph 13.

15. A method for transmitting a bitstream generated by the image encoding method according to paragraph 13.

Images