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EP-3939296-B1 - SELECTIVE INTER-COMPONENT TRANSFORM (ICT) FOR IMAGE AND VIDEO CODING

EP3939296B1EP 3939296 B1EP3939296 B1EP 3939296B1EP-3939296-B1

Inventors

  • Helmrich, Christian
  • RUDAT, Christian
  • NGUYEN, Tung Hoang
  • SCHWARZ, HEIKO
  • MARPE, DETLEV
  • WIEGAND, THOMAS

Dates

Publication Date
20260506
Application Date
20200311

Claims (13)

  1. Encoder (10, 60 1 , 60 2 ) for encoding a plurality of components of an image content region of an image to be encoded, the plurality of components corresponding to a color domain, wherein a first component C E1 of the plurality of components is a Cb component of a YCbCr scheme and wherein a second component C E2 of the plurality of components is a Cr component of the YCbCr scheme, and wherein the encoder (10, 60 1 , 60 2 ) is configured for: obtaining the plurality of components representing the image content region; selecting an intercomponent transform (62 1 , 62 2 ) from a set of intercomponent transforms, the set of intercomponent transforms comprising a plurality of intercomponent transforms (62 1 , 62 2 ) selected from the group comprising: a) one or more transforms implementing a transform-based coding; and b) at least one transform that is adapted so as to combine the first component and the second component to a common component such that the first component and the second component are represented by the common component; encoding the plurality of components using the selected intercomponent transform to obtain encoded components; and providing the encoded components, wherein when the intercomponent transform (62 1 , 62 2 ) is selected from group b, the encoder (10, 60 1 , 60 2 ) is configured for providing the common component.
  2. The encoder (10, 60 1 , 60 2 ) according to claim 1, wherein a first intercomponent transform (62 1 , 62 2 ) of the plurality of intercomponent transforms and a second intercomponent transform (62 1 , 62 2 ) of the plurality of intercomponent transforms is based on a same determination rule structure that differs with regard to at least one parameter between the first and second intercomponent transforms (62 1 , 62 2 ), wherein the encoder (10, 60 1 , 60 2 ) is configured for providing or signaling the parameter associated with the selected intercomponent transform (62 1 , 62 2 ) to a decoder (20, 65 1 , 65 2 ), wherein the parameter relates to a quantization step size of the intercomponent transform (62 1 , 62 2 ).
  3. The encoder (10, 60 1 , 60 2 ) according to any one of the preceding claims, wherein at least a first and a second intercomponent transform (62 1 , 62 2 ) of the set of intercomponent transforms are based on a transform-based coding, being based on the determination rule: C 1 = C E 1 ⋅ cos α + C E 2 ⋅ sin α ; and C 2 = − C E 1 ⋅ sin α + C E 2 ⋅ cos α ; or C 1 = C E 1 ⋅ sin α + C E 2 ⋅ cos α ; and C 2 = C E 1 ⋅ cos α − C E 2 ⋅ sin α wherein C E1 and C E2 are the first and second components, C 1 and C 2 are the results of the first and second intercomponent transforms (62 1 , 62 2 ), and α denotes a rotation angle applied for the intercomponent transform (62 1 , 62 2 ); wherein the first and the second intercomponent transform (62 1 , 62 2 ) differ with respect to each other in view of the rotation angle α; and, optionally, wherein the set of intercomponent transforms comprises at least a third intercomponent transform being based on the same determination rule and varying with regard to the rotation angle.
  4. The encoder (10, 60 1 , 60 2 ) according to claim 3, wherein the encoder (10, 60 1 , 60 2 ) is configured for selecting the intercomponent transform (62 1 , 62 2 ) by determining the rotation angle to be applied based on at least a first and a second component, preferably using a correlation-based or an intensity-based approach.
  5. Decoder (20, 65 1 , 65 2 ) configured for decoding encoded components of an image content region of a received image, the components corresponding to a color domain, wherein a first component C E1 of the plurality of components is a Cb component of a YCbCr scheme and wherein a second component C E2 of the plurality of components is a Cr component of the YCbCr scheme, and wherein the decoder (20, 65 1 , 65 2 ) is configured for: obtaining the encoded components; selecting an inverse intercomponent transform (62 1 ', 62 2 ') from a set of inverse intercomponent transforms, the set of inverse intercomponent transforms comprising a plurality of inverse intercomponent transforms (62 1 ', 62 2 ') selected from the group comprising: a) one or more inverse transforms implementing a transform-based decoding; and b) at least one transform that is adapted so as to obtain the first component and the second component from a common component representing the first component and the second component; and decoding a plurality of components representing the image content region using the selected inverse intercomponent transform (62 1 ', 62 2 ').
  6. The decoder (20, 65 1 , 65 2 ) of claim 5, wherein at least a first inverse intercomponent transform (62 1 ', 62 2 ') of the set of inverse intercomponent transforms is based on the determination rule: C D 1 ′ C D 2 ′ = cos α sin α − sin α cos α ⋅ w 1 0 0 w 2 ⋅ C E 1 ′ C E 2 ′ , wherein the determination rule represents two inverse intercomponent transforms (62 1 ', 62 2 '); wherein α represents a rotation angle in the signal space and w 1 and w 2 represent non-zero weighting factors, C' E1 and C, E2 represent reconstructed versions of the encoded components; and C D1 ' and C D2 ' represent the components derived using a transform with orthogonal basis functions at a decoder.
  7. The decoder (20, 65 1 , 65 2 ) according to one of claims 5 and 6, wherein the decoder (20, 65 1 , 65 2 ) is configured for obtaining from a received bitstream comprising the encoded components as a decoded common component representing a first component and a second component; and for selecting an inverse intercomponent transform (62 1 ', 62 2 ') that leads the decoder to determine the first component and the second component based on the determination rule: C D 1 ′ C D 2 ′ = w ⋅ sin α w ⋅ cos α ⋅ C ′ or C D 1 ′ C D 2 ′ = w ⋅ cos α w ⋅ sin α ⋅ C ′ , wherein α represents a rotation angle, w represents a scaling factor, C D1 ' and C D2 ' represent the decoded first and second component and C' represents the decoded common component.
  8. The decoder (20, 65 1 , 65 2 ) according to claim 7, wherein the decoder (20, 65 1 , 65 2 ) is configured for selecting the inverse intercomponent transform (62 1 ', 62 2 ') so as to determine the first component and the second component based on the determination rule: C D 1 ′ = C ′ , C D 2 ′ = a ⋅ C ′ or based on the determination rule C D 2 ′ = C ′ , C D 1 ′ = b ⋅ C ′ wherein a and b represent scaling factors.
  9. The decoder (20, 65 1 , 65 2 ) of one of claims 5 to 8, wherein the decoder (20, 65 1 , 65 2 ) is configured for receiving the encoded components as a residual signal; wherein decoding the selected inverse intercomponent transform (62 1 ', 62 2 ') comprises adding a reconstructed image content to the encoded components.
  10. The decoder (20, 65 1 , 65 2 ) of one of claims 5 to 9, wherein at least a first and a second inverse intercomponent transform (62 1 ', 62 2 ') of the set of inverse intercomponent transforms are based on a transform-based coding, being based on the determination rule: C D 1 ′ = C 1 ′ ⋅ cos α − C 2 ′ ⋅ sin α ; and C D 2 ′ = C 1 ′ ⋅ sin α + C 2 ′ ⋅ cos α ; or C D 1 ′ = C 1 ′ ⋅ sin α + C 2 ′ ⋅ cos α ; and C D 2 ′ = C 1 ′ ⋅ cos α − C 2 ′ ⋅ sin α wherein C D1 and C D2 are the received first and second components, C 1 ' and C 2 ' are the results of the first and second inverse intercomponent transforms (62 1 ', 62 2 '), and α denotes a rotation angle applied for the intercomponent transform; wherein the first and the second inverse intercomponent transform differ with respect to each other in view of the rotation angle α.
  11. Method for encoding a plurality of components of an image content region of an image to be encoded, the plurality of components corresponding to a color domain, wherein a first component C E1 of the plurality of components is a Cb component of a YCbCr scheme and wherein a second component C E2 of the plurality of components is a Cr component of the YCbCr scheme, and wherein the method comprises: obtaining the plurality of components representing the image content region; selecting an intercomponent transform (62 1 , 62 2 ) from a set of intercomponent transforms, the set of intercomponent transforms comprising a plurality of intercomponent transforms (62 1 , 62 2 ) selected from the group comprising: a) one or more transforms implementing a transform-based coding; and b) at least one transform that is adapted so as to combine the first component and the second component to a common component such that the first component and the second component are represented by the common component; encoding the plurality of components using the selected intercomponent transform (62 1 , 62 2 ) to obtain encoded components; and providing the encoded components, wherein when the intercomponent transform (62 1 , 62 2 ) is selected from group b, the method comprises providing the common component.
  12. Method for decoding encoded components of an image content region of a received image, the components corresponding to a color domain, wherein a first component C E1 of the plurality of components is a Cb component of a YCbCr scheme and wherein a second component C E2 of the plurality of components is a Cr component of the YCbCr scheme, and wherein the method comprising: obtaining the encoded components; selecting an inverse intercomponent transform (62 1 ', 62 2 ') from a set of inverse intercomponent transforms, the set of inverse intercomponent transforms comprising a plurality of inverse intercomponent transforms (62 1 ', 62 2 ') selected from the group comprising: a) one or more transforms implementing a transform-based decoding; and b) at least one transform that is adapted so as to obtain the first component and the second component from a common component representing the first component and the second component; and decoding a plurality of components representing the image content region using the selected inverse intercomponent transform.
  13. A computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method according to claim 11 or 12.

Description

The following description of the figures starts with a presentation of a description of an encoder and a decoder of a block-based predictive codec for coding pictures of a video in order to form an example for a coding framework into which embodiments of the present invention may be built in. The respective encoder and decoder are described with respect to Figures 1 to 3. Thereinafter the description of embodiments of the concept of the present invention is presented along with a description as to how such concepts could be built into the encoder and decoder of Figures 1 and 2, respectively, although the embodiments described with the subsequent Figures 4 and following, may also be used to form encoders and decoders not operating according to the coding framework underlying the encoder and decoder of Figures 1 and 2. Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures. In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise. Figure 1 shows an apparatus for predictively coding a picture 12 into a data stream 14 exemplarily using transform-based residual coding. The apparatus, or encoder, is indicated using reference sign 10. Figure 2 shows a corresponding decoder 20, i.e. an apparatus 20 configured to predictively decode the picture 12' from the data stream 14 also using transform-based residual decoding, wherein the apostrophe has been used to indicate that the picture 12' as reconstructed by the decoder 20 deviates from picture 12 originally encoded by apparatus 10 in terms of coding loss introduced by a quantization of the prediction residual signal. Figure 1 and Figure 2 exemplarily use transform based prediction residual coding, although embodiments of the present application are not restricted to this kind of prediction residual coding. This is true for other details described with respect to Figures 1 and 2, too, as will be outlined hereinafter. The encoder 10 is configured to subject the prediction residual signal to spatial-to-spectral transformation and to encode the prediction residual signal, thus obtained, into the data stream 14. Likewise, the decoder 20 is configured to decode the prediction residual signal from the data stream 14 and subject the pred ction residual signal thus obtained to spectral-to-spatial transformation. Internally, the encoder 10 may comprise a prediction residual signal former 22 which generates a prediction residual 24 so as to measure a deviation of a prediction signal 26 from the original signal, i.e. from the picture 12. The prediction residual signal former 22 may, for instance, be a subtractor which subtracts the prediction signal from the original signal, i.e. from the picture 12. The encoder 10 then further comprises a transformer 28 which subjects the prediction residual signal 24 to a spatial-to-spectral transformation to obtain a spectral-domain prediction residual signal 24' which is then subject to quantization by a quantizer 32, also comprised by the encoder 10. The thus quantized prediction residual signal 24" is coded into bitstream 14. To this end, encoder 10 may optionally comprise an entropy coder 34 which entropy codes the prediction residual signal as transformed and quantized into data stream 14. The prediction signal 26 is generated by a prediction stage 36 of encoder 10 on the basis of the prediction residual signal 24" encoded into, and decodable from, data stream 14. To this enc, the prediction stage 36 may internally, as is shown in Figure 1, comprise a dequantizer 33 which dequantizes prediction residual signal 24" so as to gain spectral-domain prediction residual signal 24‴, which corresponds to signal 24' except for quantization loss, followed by an inverse transformer 40 which subjects the latter prediction residual signal 24‴ to an inverse transformation, i.e. a spectral-to-spatial transformation, to obtain prediction residual signal 24ʺʺ, which corresponds to the original prediction residual signal 24 except for quantization loss. A combiner 42 of the prediction stage 36 then recombines, such as by addition, the prediction signal 26 and the prediction residual signal 24 so as to obtain a reconstructed signal 46, i.e. a reconstruction of the original signal 12. Reconstructed signal 46 may correspond to signal 12'. A prediction module 44 of predictio