Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/46—Colour picture communication systems
  • H04N1/56—Processing of colour picture signals
  • H04N1/60—Colour correction or control
  • H04N1/6016—Conversion to subtractive colour signals
  • H04N1/6019—Conversion to subtractive colour signals using look-up tables
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
  • H04N19/597—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding specially adapted for multi-view video sequence encoding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
  • H04N19/13—Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/184—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being bits, e.g. of the compressed video stream
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/30—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/44—Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/46—Embedding additional information in the video signal during the compression process
  • H04N19/463—Embedding additional information in the video signal during the compression process by compressing encoding parameters before transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
  • H04N19/96—Tree coding, e.g. quad-tree coding

Definitions

• a method for encoding a Look-Up-Table defined as a lattice of vertices is disclosed, wherein at least one value is associated with each vertex of the lattice.
• the value is a color value.
• a corresponding decoding method, encoding device and decoding device are disclosed.
• scalable video decoding consists in decoding (respectively encoding) a Base Layer (BL) bitstream and at least one Enhancement Layer (EL) bitstream.
• BL Base Layer
• EL Enhancement Layer
• BL Base Layer
• EL Enhancement Layer
• BL Base Layer
• EL Enhancement Layer
• BL Base Layer
• EL Enhancement Layer
• BL Base Layer
• EL Enhancement Layer
• BL Base Layer
• EL Enhancement Layer
• EL pictures are predicted from (possibly upsampled) decoded BL pictures.
• the color transform maps the colors of the BL color space (first color space) on the colors of the EL color space (second color space) using color information.
• a color transform is usually applied on the decoded pictures so that the transformed decoded pictures are adapted to the end device rendering capability.
• This color transform is also known as Color Mapping Function (CMF).
• CMF Color Mapping Function
• the CMF is for example approximated by a 3x3 gain matrix plus an offset (Gain- Offset model).
• the CMF is defined by 12 parameters.
• 3D Look Up Table also known as 3D LUT
• 3D LUT is used to describe such a CMF, without any a priori on the CMF model.
• the 3D LUT is much more precise because its size can be increased depending on the required accuracy.
• the 3D LUT may thus represent a huge data set. Transmitting a 3D LUT to a receiver thus requires encoding of the LUT.
• a LUT approximating a CMF associates with at least one color value in the first color space another color value in the second color space.
• a LUT allows for partitioning the first color space into a set of regions delimited by the vertices of the LUT.
• a 3D LUT associates with a triplet of color values in the first color space a set of color values.
• the set of color values can be a triplet of color values in the second color space or a set of color values representative of the color transform (e.g. locally defined CMF parameters) used to transform color values in the first color space into color values in the second color space.
• a square 3D LUT is represented as a lattice of NxNxN vertices.
• a corresponding triplet of color values (V c i , V C 2, V C 3) needs to be stored.
• the amount of data associated with the 3D LUT is NxNxNxK, where K is the amount of bits used to store one LUT triplet value .
• the triplet value is for example a (R, G, B) triplet, a (Y, U, V) triplet or a (Y, Cb,Cr) triplet, etc. Encoding all the vertex values is not efficient since it represents a huge amount of data.
• a method for encoding a LUT defined as a lattice of vertices is disclosed. At least one value is associated with each vertex of the lattice.
• the encoding method comprises for a current vertex:
• the another value is obtained from reconstructed values associated with neighboring vertices.
• the value is a color value.
• the color value is representative of a color transform.
• the color value is a gain parameter or an offset.
• the LUT is a 3D LUT encoded using an octree and three values are associated with each vertex of the lattice.
• the neighboring vertices used for prediction belong to a parent octant of a current octant to which the current vertex belongs.
• predicting the at least one value associated with the current vertex from reconstructed values associated with neighboring vertices comprises interpolating the at least one value from corresponding reconstructed values of the neighboring vertices.
• the method further comprises encoding an index in the bitstream indicating a type of interpolation.
• encoding at least one residue comprises quantizing the at least one residue with a quantizer into a quantized residue and entropy coding the quantized residue in the bitstream and wherein the method further comprises encoding the quantizer in the bitstream.
• a flag is encoded for the current vertex indicating whether or not at least one residue is encoded for the vertex.
• a flag is encoded for each value of the current vertex indicating if a residue is encoded for that value or if the residue is not encoded and is inferred to be zero.
• a split flag is encoded for the current octant indicating if its immediate children are recursively encoded or if all the residues of the vertices of all its children not yet encoded are inferred to be zero.
• a method for decoding a LUT defined as a lattice of vertices is also disclosed. At least one value is associated with each vertex of the lattice.
• the decoding method comprises for a current vertex:
• the another value is obtained from reconstructed values associated with neighboring vertices.
• the value is a color value.
• the color value is representative of a color transform.
• the color value is a gain parameter or an offset.
• the LUT being a 3D LUT decoded using an octree and three values being associated with each vertex of the lattice, the neighboring vertices belong to a parent octant of a current octant to which the current vertex belong.
• predicting the at least one value associated with the current vertex from reconstructed values associated with neighboring vertices comprises interpolating the at least one value from corresponding reconstructed values of the neighboring vertices.
• the method further comprises decoding an index from the bitstream indicating a type of interpolation.
• decoding at least one residue comprises entropy decoding a quantized residue from the bitstream and inverse quantizing the quantized residue with a quantizer into a decoded residue and wherein the method further comprises decoding the quantizer from the bitstream.
• a flag is decoded for each vertex indicating whether or not at least one residue is encoded for the vertex.
• a flag is decoded for each value of the current vertex indicating if a residue is decoded for that value or if the residue is inferred to be zero.
• a split flag is decoded for the current octant indicating if its immediate children are recursively decoded or if all the residues of the vertices of all its children not yet decoded are inferred to be zero.
• the another value is obtained from reconstructed values associated with neighboring vertices.
• the encoder is configured to execute the steps of the method for encoding.
• a decoder for decoding a LUT defined as a lattice of vertices, wherein at least one value is associated with each vertex of the lattice comprising:
• the another value is obtained from reconstructed values associated with neighboring vertices.
• the encoder is configured to execute the steps of the method for decoding.
• a bitstream encoding at least a LUT defined as a lattice of vertices is disclosed. At least one value is associated with each vertex of the lattice and the bitstream comprises encoded in it at least one residue computed between the at least one value of a current vertex and its prediction. 4. BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates an architecture of a scalable video decoder that uses gamut scalability according to the prior art
• FIG. 2 illustrates an architecture of a video decoder that comprises color transform to adapt to rendering display characteristics according to the prior art
• - Figure 3 diagrammatically shows a square 3D LUT represented as a lattice of NxNxN vertices according to the prior art
• FIG. 4 depicts a flowchart of an encoding method according to an exemplary embodiment of the invention
• FIG. 6 represents a flowchart of an encoding method according to another exemplary embodiment of the invention.
• Figures 7A and 7B diagrammatically shows on the left a recursive subdivision of a cube into octants and on the right a corresponding octree;
• FIG. 8 illustrates an interpolation of the color values of a vertex according to the invention
• FIG. 9A diagrammatically shows a 3D LUT represented as a nonuniform lattice
• FIG. 9B illustrates the prediction of a value associated with a vertex according specific and non limitative embodiment
• FIG. 9C represents an octant in which only 4 out of 8 vertices are encoded
• FIG. 10 represents a flowchart of a decoding method according to an exemplary embodiment of the invention.
• FIG. 1 1 represents a flowchart of a decoding method according to another exemplary embodiment of the invention.
• FIG. 12 diagrammatically shows an encoder for encoding a LUT according to the invention
• FIG. 13 diagrammatically shows a decoder for decoding a LUT according to the invention.
• Figure 4 represents a flowchart of an encoding method according to an exemplary embodiment of the invention.
• the method is for encoding a LUT defined as a lattice of vertices, wherein at least one value, e.g. a color value, is associated with each vertex of the lattice.
• a color value comprises color values of a given color space such as RGB, YUV or Y,Cb,Cr values and further comprises values representative of a color transform such as CMF parameters, i.e. matrix parameters and offset values.
• the at least one color value of a current vertex is predicted from reconstructed color values associated with neighboring vertices.
• a 2D LUT associating with a vertex V0(c1 0 ,c2 0 ) a corresponding pair of values (V0 c i , V0 C 2), e.g. color values, is depicted on Figure 5.
• the values associated with the vertex V0 are predicted for example from spatially neighboring vertices V1 (c1 i ,c2i), V2(c1 2 ,c2 2 ), V3(c1 3 ,c2 3 ) and V4(c1 4 ,c2 4 ) with corresponding pair of values (Vi c i ,
• a prediction P(Pc1 , Pc2) is for example computed using interpolation as follows:
• the 2D LUT associates with the vertex V0(c1 0 ,c2 0 ) a set of parameters (m1 1 , m12, m21 , m22, o1 , o2) instead of the pair of values (VOd , V0c 2 )-
• This set of parameters can be used to reconstruct the values (VOd , V0c2) from the values (c1 0 ,c2 0 ) of V0 as follows:
• V0ci m1 1 * c1 0 +m12 * c2 0 +o1
• V0c 2 m21 * c1 0 +m22 * c2 0 +o2
• the parameters associated with the vertex V0 are predicted for example from reconstructed parameters associated with spatially neighboring vertices V1 (c1 i,c2i), V2(c1 2 ,c2 2 ), V3(c1 3 ,c2 3 ) and V4(c1 4 ,c2 4 ).
• a prediction is for example computed for a parameter of the current vertex using interpolation.
• at least one residue is determined between the at least one color value of the current vertex and its prediction and is further encoded in a bitstream F. The residue is determined by subtracting from the at least one color value of the current vertex its prediction.
• the encoding usually comprises entropy encoding. According to a variant the encoding comprises quantizing the residue with a quantizer q and entropy encoding the quantized residue.
• first and second residues are computed for the vertex V0.
• the first residue is equal to (V0 c i- Pel ) and the second residue is equal to (V0 C 2- Pc2).
• the residues or the quantized residues (V0 c i - Pc1 )/q and (V0 C 2- Pc2)/q are then entropy coded in the bitstream F.
• the entropy coding makes use of traditional binary coding techniques such as Exponential-Golomb, Huffman, CABAC (English acronym of "Context Adaptive Binary Arithmetic Coding").
• the steps 40 and 42 are iterated to encode a further vertex of the LUT until all the vertices of the LUT are encoded.
• the encoding method comprises encoding in the bitstream F the quantizer value q.
• the at least one color value of the current vertex is further reconstructed to be used for the prediction of other vertices.
• the encoding method further comprises encoding in the bitstream F the interpolation type used for predicting the at least one color value of the vertex. More precisely an index is decoded from the bitstream that identify an interpolation type.
• the index 0 identifies the bilinear interpolation
• an index 1 identifies nearest neighbor interpolation
• an index 2 identifies linear interpolation with 2 nearest neighbors.
• a binary flag is thus encoded in the bitstream for each vertex indicating if at least one residue is encoded for that vertex or if none of the residues are encoded and are thus inferred to be zero.
• a binary flag is encoded for each color value of each vertex indicating if a residue is encoded for that color value or if the residue is not encoded and is inferred to be zero.
• the size of the LUT is also optionally encoded in the bitstream.
• FIG. 6 represents a flowchart of an encoding method according to another exemplary embodiment of the invention.
• the method is for encoding a 3D LUT defined as a lattice of vertices using an octree, wherein a set of n color values such as a triplet of color values is associated with each vertex of the lattice, where n is an integer > 1 .
• An octree is for partitioning a 3D color space by recursively subdividing it into eight octants as depicted on Figures 7A and 7B. On figure 7A the partitioning is symmetric while on figure 7B the partitioning is asymmetric.
• An Octant of level N has its parent octant in level N-1 .
• Octrees are the 3D analog of quadtrees.
• each of the three color values (V r , V g , V b ) associated with the current vertex V of coordinates (r, g, b) is predicted from reconstructed color values associated with neighboring vertices, i.e. vertices which belong to a parent octant of the current octant, (r, g, b) is used instead of (d , c2, c3) for simplifying the notations.
• the invention is not limited to the (R, G, B) color space. It can be applied to (Y,U,V), (Y,Cb,Cr), ... color spaces representations.
• r is the first color value associated with the vertex (ri, gj, bk);
• the lattice is not necessarily uniform as depicted on Figure 9A.
• each of the three color values (V r , V g , V b ) associated with the current vertex V of coordinates (r, g, b) of a current octant of index j is predicted from at least one reconstructed color value associated with one neighboring vertex Vp of coordinates (r p , g p , b p ), i.e. a vertex which belongs to a neighboring octant of index (j-1 ).
• a neighboring octant is an octant sharing at least one vertex with the current octant and/or preceding the current octant in the coding octant list.
• a coding octant list is a list specifying the order of coding of the octant. In a specific embodiment all the octants belong to one and the same level.
• PredB r V'r- PredAV, where V'r is the reconstructed color value of the vertex Vp of a neighboring octant and PredAV is a value that depends on the position of the vertex Vp in the 3D LUT. PredAV is for example equal to r p .
• the same equations are used for g and b.
• the residues are then entropy coded in a bitstream or quantized before being entropy coded.
• the entropy coding makes use of traditional binary coding techniques such as Exponential-Golomb, Huffman, CABAC (English acronym of "Context Adaptive Binary Arithmetic Coding").
• the octant of level 0 has not parent octant.
• the first octant in the coding octant list has no preceding octant. Consequently, each of the three color values (V r , V g , V b ) associated with a current vertex V of this octant is predicted from a known color value, e.g. the value 128.
• a known color value e.g. the value 128.
• different known values are used for the different vertices of the octant of level 0.
• predicting from known color values is also made for other octants than the octant of level 0.
• each of the three color values (V r , V g , V b ) associated with a current vertex V of this octant is predicted from already reconstructed color values associated with neighboring vertices which belong to the same octant.
• the encoding method comprises encoding in the bitstream the quantizer value q.
• the three color values of the current vertex are further reconstructed and can be used for the prediction of other vertices.
• the encoding method further comprises encoding in the bitstream the interpolation type used for predicting the at least one color value of the vertex. More precisely an index is encoded in the bitstream that identifies an interpolation type.
• the index 0 identifies the trilinear interpolation
• the index 1 identifies a prism interpolation
• the index 2 identifies a pyramidal interpolation
• the index 3 identifies a tetrahedral interpolation.
• a binary flag is thus encoded in the bitstream for each vertex indicating whether or not at least one residue is encoded for that vertex.
• a binary flag is encoded for each color value of each vertex indicating if a residue is encoded for that color value or if the residue is not encoded and is inferred to be zero.
• only specific vertices are encoded as depicted on figure 9C. On this figure only 4 out of 8 vertices are encoded per octant.
• the LUT is usually encoded in a bitstream for being used to transform pictures of a video in applications such as rendering display color adaptation or color gamut scalability.
• the LUT may be encoded and transmitted with the video. If the encoding method knows that some parts of the 3D LUT is not to be used by the application, then the vertices that belong to this part of the 3D LUT are not encoded. In the same way, if the encoding method knows that some parts of the 3D LUT have small impacts on the final rendering of the video, then the vertices that belong to this part of the 3D LUT are not encoded.
• the method is applied recursively for encoding the whole 3D LUT.
• all the octants of the octree are encoded.
• the vertices of the children octant of the current octant are encoded.
• the 3D LUT is pre-processed before being encoded.
• a split flag is associated with each octant in the octree and is initially set to false.
• the split flag values are determined for each octant. If at least one vertex to be encoded of a current octant has at least one residue possibly quantized greater than TH, then the split flag of its parent octant is set to "true".
• the split flag of a current octant of level N thus indicates if its immediate children (i.e. children of level N+1 ) are recursively encoded or if all the residues of the vertices of all its children (i.e. children of level N+k with k>0) not yet encoded are inferred to be zero.
• the split flags and the residues are encoded in the bitstream.
• the vertices of the children octant of the current octant are encoded if current octant split flag is true.
• the vertices that belong to two octants are preferentially encoded only once.
• the vertices shared between several octants are encoded more than once. Specifically, the vertices are encoded several times with different values, one value for each octant it belongs to. With reference to figure 9D, the vertex V1 is shared between the octant (j) and the octant (j-1 ).
• V1 can be encoded twice with one value for the octant (j) and another value for the octant (j-1 ).
• the first value and the another value may be different.
• the vertex V2 that is shared between 4 octants can be encoded 4 times.
• the 3D LUT is for example encoded in the VPS ("Video Parameter Set”), SPS ("Sequence Parameter Set”), PPS ("Picture Parameter Set”) or in one SEI message ("Supplemental Enhancement Information") as defined in AVC, HEVC, SVC or SHVC video coding standards.
• VPS Video Parameter Set
• SPS Sequence Parameter Set
• PPS Position Parameter Set
• SEI message Supplemental Enhancement Information
• the 3D LUT is for example encoded in a SEI message such as the one defined below.
• the size S of the LUT is also optionally encoded in the bitstream. S is the number of vertices in one direction.
• a flag is encoded indicating to the decoder to compute a 3x3 gain matrix plus an offset from the decoded 3D LUT and to use it as CMF instead of the 3D LUT.
• one 3D LUT composed of vertices with n associated color values is used to encode parameters of a color transform defined locally.
• each vertex of the 3D LUT is associated with 1 2 color values representative of a color transform.
• Figure 10 represents a flowchart of a decoding method according to an exemplary embodiment of the invention.
• a step 140 at least one residue is decoded from a bitstream F.
• the decoding usually comprises entropy decoding.
• the decoding comprises entropy decoding of a quantized residue and inverse quantizing of the quantized residue with a quantizer q.
• the entropy decoding makes use of traditional binary decoding techniques such as Exponential- Golomb, Huffman, CABAC (English acronym of "Context Adaptive Binary Arithmetic Coding").
• the decoding method comprises decoding from the bitstream F the quantizer value q.
• not all the vertices of the LUT are encoded in the bitstream F.
• a binary flag is decoded from the bitstream for each vertex indicating whether or not at least one residue is encoded for that vertex. If no residue is encoded, the residue(s) is/are assumed to be zero for this vertex.
• the at least one color value of a current vertex is predicted from reconstructed color values associated with neighboring vertices.
• a 2D LUT associating with a vertex V0(c1 ,c2) a corresponding pair of color values (V0 c i, V0 C2 ) is depicted on Figure 5.
• the color values associated with vertex V0 are predicted from spatially neighboring vertices V1 , V2, V3 and V4.
• a predictor P(Pc1 , Pc2) is computed using interpolation as follows:
• the 2D LUT associates with the vertex V0(c1 0 ,c2 0 ) a set of parameters (m1 1 , m12, m21 , m22, o1 , o2) instead of the pair of values (VO d , V0c 2 )-
• the parameters associated with the vertex VO are predicted for example from reconstructed parameters associated with spatially neighboring vertices V1 (c1 1 ,c2 1 ), V2(c1 2 ,c2 2 ), V3(c1 3 ,c2 3 ) and V4(c1 4 ,c2 4 ).
• a prediction is for example computed for a parameter of the current vertex using interpolation.
• a vertex is reconstructed. More precisely, at least one color value of the current vertex is reconstructed from its prediction and the decoded at least one residue.
• the decoding method further comprises decoding from the bitstream F the interpolation type used for predicting the at least one color value of the vertex. More precisely an index is decoded from the bitstream that identify an interpolation type.
• the index 0 identifies the bilinear interpolation and an index 1 identifies a nearest vertices value interpolation.
• the size of the LUT is also optionally decoded from the bitstream.
• Figure 11 represents a flowchart of a decoding method according to another exemplary embodiment of the invention.
• the method is for decoding a 3D LUT defined as a lattice of vertices using an octree, wherein a triplet of color values is associated with each vertex of the lattice.
• the decoding method is disclosed for the decoding a current vertex V of the lattice that belongs to a current octant.
• a step 150 three residues res r , res g , resb are decoded from a bitstream F.
• the decoding usually comprises entropy decoding.
• the decoding comprises entropy decoding of a quantized residue and inverse quantizing of the quantized residue with a quantizer q.
• the entropy decoding makes use of traditional binary decoding techniques such as Exponential- Golomb, Huffman, CABAC (English acronym of "Context Adaptive Binary Arithmetic Coding").
• the decoding method comprises decoding from the bitstream F the quantizer value q.
• not all the vertices of the LUT are encoded in the bitstream F.
• a binary flag is decoded from the bitstream for each vertex indicating whether or not at least one residue is encoded for that vertex. If no residue is encoded, the residue(s) is/are assumed to be zero for this vertex.
• only specific vertices are decoded as depicted on figure 9C. On this figure only 4 out of 8 vertices are decoded per octant.
• each of the three color values (V r , V g , V b ) associated with the current vertex V of coordinates (r, g, b) is predicted from reconstructed color values associated with neighboring vertices, i.e. vertices which belong to a parent octant of the current octant, (r, g, b) is used instead of (d , c2, c3) for simplifying the notations.
• the invention is not limited to the (R, G, B) color space. It can be applied to (Y,U,V), (Y,Cb,Cr), ... color spaces representations.
• a prediction is thus determined for each color value.
• r is the first color value associated with the vertex (ri, gj, bk);
• each of the three color values (V r , V g , V b ) associated with the current vertex V of coordinates (r, g, b) of a current octant of index j is predicted from at least one reconstructed color value associated with one neighboring vertex Vp of coordinates (r p , g p , b p ), i.e. a vertex which belongs to a neighboring octant of index (j-1 ).
• a neighboring octant is an octant sharing at least one vertex with the current octant and/or preceding the current octant in the coding octant list.
• a coding octant list is a list specifying the order of coding of the octant. In a specific embodiment all the octants belong to one and the same level.
• PredB r V'r- PredAV, where V'r is the reconstructed color value of the vertex Vp of a neighboring octant and PredAV is a value that depends on the position of the vertex Vp in the 3D LUT. PredAV is for example equal to r p .
• the same equations are used for g and b.
• a step 1 54 three color values are computed thus reconstructed for the current vertex from their prediction and the corresponding decoded residues (res r , resg , res b ).
• the current vertex is thus reconstructed by computing its three color values as follows: (res r + V r ), (res g + V g )) and (res b + ).
• the octant of level 0 has not parent octant.
• the first octant in the coding octant list has no preceding octant. Consequently, each of the three color values (V r , V g , V b ) associated with a current vertex V of this octant is predicted from a known color value, e.g. the value 1 28.
• each of the three color values (V r , V g , V b ) associated with a current vertex V of this octant is predicted from already reconstructed color values associated with neighboring vertices which belong to the same octant.
• the method is applied recursively for decoding the whole 3D LUT.
• the vertices that belong to two octants are preferentially decoded only once.
• the vertices shared between several octants are decoded more than once.
• the vertices are decoded several times with different values, one value for each octant it belongs to.
• the vertex V1 is shared between the octant (j) and the octant (j-1 ). Therefore, V1 can be decoded twice with one value for the octant (j) and another value for the octant (j-1 ). The first value and the another value may be different.
• the vertex V2 that is shared between 4 octants can be decoded 4 times. Once all the vertices of a current octant (level N) are decoded, the vertices of the children (level N+1 ) octants of the current octant are decoded.
• a split flag is decoded for a current octant of level N that indicates if its immediate children (i.e. children of level N+1 ) are recursively decoded or if all the residues of the vertices of all the children (i.e. children of level N+k with k>0) not yet decoded are inferred to be zero.
• the decoding method further comprises decoding from the bitstream F the interpolation type used for predicting the at least one color value of the vertex. More precisely an index is decoded from the bitstream that identify an interpolation type.
• the index 0 identifies the trilinear interpolation
• the index 1 identifies a prism interpolation
• the index 2 identifies a pyramid interpolation
• the index 3 identifies a tetrahedral interpolation.
• the 3D LUT is for example decoded from the VPS, SPS, PPS or in one SEI message as defined in AVC, HEVC, SVC or SHVC video coding standards.
• the size of the LUT is also optionally decoded from the bitstream.
• the 3D LUT is for example decoded in a SEI message such as the one defined below.
• a flag is decoded indicating to the decoder to compute a 3x3 gain matrix plus an offset from the decoded 3D LUT and to use it as CMF instead of the 3D LUT.
• aspects of the present principles can be embodied as a system, method or computer readable medium. Accordingly, aspects of the present principles can take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, and so forth), or an embodiment combining software and hardware_aspects that can all generally be referred to herein as a "circuit,” "module”, or “system.” Furthermore, aspects of the present principles can take the form of a computer readable storage medium. Any combination of one or more computer readable storage medium(s) may be utilized.
• each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s).
• the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, or blocks may be executed in an alternative order, depending upon the functionality involved.
• a bitstream is also disclosed that encodes a LUT such as a 3D LUT.
• the bitstream produced by the encoding method of figure encoding at least a LUT defined as a lattice of vertices, wherein at least one color value is associated with each vertex of the lattice, wherein said bitstream comprises encoded in it at least one residue computed between the at least one color value of a current vertex and its prediction.
• An exemplary embodiment is proposed within the framework of the HEVC coding standard defined in document JCTVC-L1003 of Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1 1 or the SHVC coding standard which is the scalable extension of the HEVC coding standard defined in document JCTVC-L1008 of Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/I EC JTC1 /SC29/WG1 1 .
• the standard defines a syntax that any stream of coded data must comply with to be compatible with this standard.
• the syntax defines in particular how the various items of information are coded (for example the data relating to the pictures included in the sequence, the motion vectors, etc).
• the LUT can be encoded into the PPS or the VPS.
• the syntax element, use_color_prediction is used to indicate the use of color prediction in the current picture as shown in Table 1 .
• Table 1 signaling of the prediction parameters If the use_color_prediction flag is equal to , the 3D_ LUT_ color_data function is called to signal 3D LUT data as shown in Table 2.
• nbpCode indicates the 3D LUT size as listed in Table 4 for the given value of nbpCode.
• the quantizer value can be encoded by the 3D_ LUT_ color_data() function.
• 3D_ LUT_ color_data ( ) is defined as follows in table 3.
• nbpCode indicates the 3D LUT size as listed in Table 4 for the given value of nbpCode.
• the quantizer value can be encoded by the 3D_ LUT_ color_data() function.
• NbitsPerSample indicates a number of bits used to represent the color values.
• the LUT is encoded in a SEI message (SEI stands for "Supplemental Enhancement Information").
• SEI Supplemental Enhancement Information
• the HEVC standard defines in its Annex D the way in which additional information termed SEI is coded. This additional information is referenced in the syntax by a field called payloadType.
• SEI messages assist for example in processes related to display. Note that if the decoding device does not possess the functionalities necessary for its use, this information is ignored.
• a new type of SEI message is defined so as to code additional information relating to the 3D LUT. For this purpose, a new value for the field payloadType is defined from among the values not yet used (for example payloadType is equal to 24).
• the syntax of the SEI data (i.e. sei_payload) is extended in the following manner:
• the SEI message further comprises an indicator color_interpolator_id, e.g. after color_description_present_flag, whose value indicates a type of interpolation as specified in Table 7.
• This SEI message provides information to enable remapping of the color samples of the output decoded pictures for customization to particular display environments.
• the remapping process maps coded sample values in the RGB color space to target sample values.
• the mappings are expressed either in the luma or RGB color space domain, and should be applied to the luma component or to each RGB component produced by color space conversion of the decoded picture accordingly.
• 3D_ LUT_ color_data ( ) is defined in Table 2 or 3.
• the decoded 3D LUT is applied to decoded pictures belonging to a layer identified for example by the index nuh_layer_id of the NAL Unit Header (see section 7.3.1 .2 of document HEVC coding standard defined in document JCTVC-L1003 of Joint Collaborative Team on Video Coding (JCT-VC) of ITU- T SG16 WP3 and ISO/I EC JTC1 /SC29/WG1 1 of the SEI message.
• JCT-VC Joint Collaborative Team on Video Coding
• color_map_id contains an identifying number that may be used to identify the purpose of the color mapping model. Values of color_map_id may be used as determined by the application. The color_map_id can be used to support color mapping operations that are suitable for different display scenarios. For example, different values of color_map_id may correspond to different display bit depths.
• color_map_cancel_flag 1 indicates that the color mapping information SEI message cancels the persistence of any previous color mapping information SEI message in output order.
• color_map_cancel_flag 0 indicates that color mapping information follows.
• color_map_repetition_period specifies the persistence of the color mapping information SEI message and may specify a picture order count interval within which another color mapping information SEI message with the same value of color_map_id or the end of the coded video sequence shall be present in the bitstream.
• color_map_repetition_period equal to 0 specifies that the color map information applies to the current decoded picture only.
• color_map_repetition_period 1 specifies that the color map information persists in output order until any of the following conditions are true:
• a picture in an access unit containing a color mapping information SEI message with the same value of color_map_id is output having a picture order count (known as POC) greater than the POC of the current decoded picture, denoted PicOrderCnt( CurrPic ).
• color_map_repetition_period 0 or equal to 1 indicates that another color mapping information SEI message with the same value of color_map_id may or may not be present.
• color_map_repetition_period greater than 1 specifies that the color map information persists until any of the following conditions are true:
• a picture in an access unit containing a color mapping information SEI message with the same value of color_map_id is output having a POC greater than PicOrderCnt( CurrPic ) and less than or equal to PicOrderCnt( CurrPic ) + color_map_repetition_period.
• color_map_repetition_period greater than 1 indicates that another color mapping information SEI message with the same value of color_map_id shall be present for a picture in an access unit that is output having a POC greater than PicOrderCnt( CurrPic ) and less than or equal to PicOrderCnt( CurrPic ) + color_map_repetition_period; unless the bitstream ends or a new coded video sequence begins without output of such a picture.
• color_description_present_flag 1 specifies that colour_primaries_input_id and colour_primaries_output_id are present.
• colour_description_present_flag 0 specifies that colour_primaries_input_id and colour_primaries_output_id are not present.
• color_primaries_input_id indicates the chromaticity coordinates of the source primaries as specified in Table 8 in terms of the CIE 1931 definition of x and y as specified by ISO 1 1664-1 .
• color_primaries_output_id indicates the chromaticity coordinates of the color mapped primaries as specified in Table 8 in terms of the CIE 1931 definition of x and y as specified by ISO 1 1664-1 , once the 3D color lut is applied.
• color_output_rgb 1 specifies the output color samples are luma and chroma signals.
• color_output_rgb 0 specifies the output color samples are green, red, blue values.
• Iut_bit_depth_minus8 specifies the bit depth of the 3D LUT samples.
• nbp_code indicates the 3D LUT size nbp as listed in Table 4 for the given value of nbp_code.
• the ouput of the 3D LUT decoding is a 3 dimension array LUTof size nbp x nbp x nbp.
• Each LUT array element is called a vertex and is associated with 3 reconstructed sample values (recSamplesY, recSamplesU, recSamplesV) of bit depth equal to (lut_bit_depth_minus8+8).
• a vertex lut[i][j][k] is said to belonging to layer layer_id if the values of i%(nbp»layer_id), j%(nbp»layer_id), k%(nbp»layer_id) are equal to zero.
• One vertex may belong to several layers.
• An octant of layer layer_id is composed of 8 neighboring vertices belonging to layer_id ( Figure 14).
• the decoding of the octant( layer_id, y,u,v) is a recursive function.
• the component values are reconstructed by adding the residuals to the prediction of the components values.
• the prediction of the components values is computed using tri-linear interpolation of the 8 neighboring vertices of layer_id-1 . Once reconstructed a vertex is marked as reconstructed.
• Figure 12 represents an exemplary architecture of an encoder 1 .
• the encoder is configured to execute the steps of the encoding method.
• Encoder 1 comprises following elements that are linked together by a data and address bus 64:
• microprocessor 61 which is, for example, a DSP (or Digital Signal Processor);
• ROM Read Only Memory
• I/O devices 65 such as for example a keyboard, a mouse, a webcam; and
• the power source 66 is external to the encoder.
• the word « register » used in the specification designates in each of the memories mentioned, both a memory zone of low capacity (some binary data) as well as a memory zone of large capacity (enabling a whole program to be stored or all or part of the data representative of data calculated or to be displayed).
• ROM 62 comprises a program and encoding parameters (such as threshold TH). Algorithm of the encoding method according to the invention is stored in the ROM 62. When switched on, the CPU 61 uploads the program 620 in the RAM and executes the corresponding instructions.
• RAM 63 comprises, in a register, the program executed by the CPU 61 and uploaded after switch on of the encoder 1 , input data in a register, encoded data in different state of the encoding method in a register and other variables used for encoding in a register.
• Figure 13 represents an exemplary architecture of a decoder 2. The decoder is configured to execute the steps of the decoding method. Decoder 2 comprises following elements that are linked together by a data and address bus 74:
• microprocessor 71 which is, for example, a DSP (or Digital Signal Processor);
• ROM Read Only Memory
• the battery 76 is external to the encoder.
• the word « register » used in the specification can correspond to area of small capacity (some bits) or to very large area (e.g. a whole program or large amount of received or decoded data).
• ROM 72 comprises at least a program and decoder parameters. Algorithm of the decoding method according to the invention is stored in the ROM 72. When switched on, the CPU 71 uploads the program 720 in the RAM and executes the corresponding instructions.
• RAM 73 comprises, in a register, the program executed by the CPU 71 and uploaded after switch on of the decoder 2, input data in a register, decoded data in different state of the decoding method in a register, and other variables used for decoding in a register.
• the implementations described herein may be implemented in, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method or a device), the implementation of features discussed may also be implemented in other forms (for example a program).
• An apparatus may be implemented in, for example, appropriate hardware, software, and firmware.
• the methods may be implemented in, for example, an apparatus such as, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device.
• processors also include communication devices, such as, for example, computers, cell phones, portable/personal digital assistants ("PDAs"), and other devices that facilitate communication of information between end-users.
• PDAs portable/personal digital assistants
• Implementations of the various processes and features described herein may be embodied in a variety of different equipment or applications, particularly, for example, equipment or applications.
• equipment examples include an encoder, a decoder, a post-processor processing output from a decoder, a pre-processor providing input to an encoder, a video coder, a video decoder, a video codec, a web server, a set-top box, a laptop, a personal computer, a cell phone, a PDA, and other communication devices.
• the equipment may be mobile and even installed in a mobile vehicle.
• the methods may be implemented by instructions being performed by a processor, and such instructions (and/or data values produced by an implementation) may be stored on a processor-readable medium such as, for example, an integrated circuit, a software carrier or other storage device such as, for example, a hard disk, a compact diskette (“CD"), an optical disc (such as, for example, a DVD, often referred to as a digital versatile disc or a digital video disc), a random access memory (“RAM”), or a read-only memory (“ROM”).
• the instructions may form an application program tangibly embodied on a processor-readable medium. Instructions may be, for example, in hardware, firmware, software, or a combination.
• a processor may be characterized, therefore, as, for example, both a device configured to carry out a process and a device that includes a processor-readable medium (such as a storage device) having instructions for carrying out a process. Further, a processor-readable medium may store, in addition to or in lieu of instructions, data values produced by an implementation.
• implementations may produce a variety of signals formatted to carry information that may be, for example, stored or transmitted.
• the information may include, for example, instructions for performing a method, or data produced by one of the described implementations.
• a signal may be formatted to carry as data the rules for writing or reading the syntax of a described embodiment, or to carry as data the actual syntax-values written by a described embodiment.
• Such a signal may be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal.
• the formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream.
• the information that the signal carries may be, for example, analog or digital information.
• the signal may be transmitted over a variety of different wired or wireless links, as is known.
• the signal may be stored on a processor- readable medium.

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