Method for decoding a digital image, coding method, devices, and associated computer programs

A decoding device comprising:

• a processor;
• and
• a non-transitory computer-readable medium comprising instructions stored thereon, which when executed by the processor configure the decoding device to perform acts comprising:
• receiving from a communication network a bit stream comprising coded data representative of at least one digital image;
• and
• decoding the at least one digital image, said image being divided into a plurality of blocks processed in a defined order, wherein the decoding implements, for a current block block:
• decoding coefficients of the current block from the coded data read in the bit stream;
• transforming the current block into a decoded block, said current block comprising M row vectors and N columns vectors, with M and N being non-zero integers, said transforming implementing a first transforming producing an intermediate block, applying to the column vectors respectively row vectors of the current block, and a second transforming producing a block of pixels applying to the row vectors respectively column vectors of the intermediate block, resulting from the first transforming;
• rebuilding the image from the decoded block;
• wherein:
• at least one of said first and second transforming comprises, for a row vector respectively a column vector, called an input vector:
• forming a first subvector of size K<N respectively M from adjacent elements of the input vector and at least one second subvector of size equal to N−K or M−K respectively from adjacent elements of the input vector, not included in the first subvector, such that the sum of the sizes of the formed subvectors is equal to the size of the input vector;
• transforming the first subvector into a first transformed subvector by applying a first partial subtransform of size K×K and transforming the second subvector into a second transformed subvector by applying a second subtransform of size (N−K)×(N−K);
• and
• building the transformed vector of the intermediate block for the first transforming, respectively of the transformed decoded block for the second transforming, by inserting the first transformed subvector and the at least one second transformed subvector.

A method comprising the following acts performed by an encoding device:

• encoding at least one digital image, said image being divided into a plurality of blocks of pixels processed in a defined order, said encoding comprising the following steps, implemented for a current block of predetermined dimensions:
• transforming the current block into a transformed block, said current block comprising M row vectors and N column vectors, with M and N being non-zero integers, said transforming comprising a first substep of transformation of the M row vectors, respectively column vectors, to provide an intermediate block formed from the transformed row vectors, respectively column vectors, and a second substep of transformation of the N column vectors, respectively row vectors of the intermediate block;
• encoding the transformed block to produce coded data representative of the transformed block;
• inserting the coded data into a bit stream representative of the coded image;
• and
• transmitting the bit stream over a communication network;
• wherein
• at least one of said first and second transformation sub-steps comprises, for a row vector respectively a column vector, called an input vector:
• forming a first subvector of size K<N respectively N from adjacent elements of the input vector and at least one second subvector of size equal to N−K respectively M−K respectively from adjacent elements of the input vector, not included in the first sub-vector, such that the sum of the sizes of the formed subvectors is equal to the size of the input vector;
• transforming the first subvector into a first transformed subvector by applying a first partial subtransform of size K×K and transforming the second subvector into a second transformed subvector by applying a second subtransform of size (N−K)×(N−K);
• and
• building a transformed row vector respectively a transformed column vector of the intermediate block for the first transformation substep, respectively of the decoded block transformed for the second transformation step, by inserting the first transformed subvector and the at least one second transformed subvector.

An encoding device comprising:

• a processor;
• and
• a non-transitory computer-readable medium comprising instructions stored thereon, which when executed by the processor configure the encoding device to perform acts comprising:
• encoding at least one digital image, said image being divided into a plurality of blocks of pixels processed in a defined order, said encoding comprising the following steps, implemented for a current block of predetermined dimensions:
• transforming the current block into a transformed block, said current block comprising M row vectors and N column vectors, with M and N being non-zero integers, said transforming comprising a first transformation of the M row vectors, respectively column vectors, to provide an intermediate block formed from the transformed row vectors, respectively transformed column vectors, and a second transformation of the M column vectors, respectively row vectors of the intermediate block;
• encoding the transformed block to produce coded data representative of the transformed block;
• building a bit stream representative of the coded image configured to insert said coded data in the bit stream;
• and
• transmitting the bit stream over a communication network;
• wherein
• at least one of said first and second transformations comprises, for a row vector respectively a column vector, called input vector:
• forming a first subvector of size K<N respectively M from adjacent elements of the input vector and at least one second subvector of size equal to N−K respectively M−K respectively from adjacent elements of the input vector, not included in the first sub-vector, such that the sum of the sizes of the formed subvectors is equal to the size of the input vector;
• transforming the first subvector into a first transformed subvector by applying a first partial subtransform of size K×K and transforming the second subvector into a second transformed subvector by applying a second subtransform of size (N−K)×(N−K);
• and
• building a transformed row vector, respectively a transformed column vector, of the intermediate block for the first transformation, respectively of the transformed decoded block for the second transformation, by inserting the at least one first transformed subvector and the at least one second transformed subvector.

A non-transitory computer-readable medium comprising a computer program stored thereon, which comprises instructions for implementing a decoding method when executed by a processor of a decoding device, wherein the method comprises:

• receiving from a communication network a bit stream comprising coded data representative of at least one digital image;
• and
• decoding the at least one digital image, said image being divided into a plurality of blocks processed in a defined order, said decoding comprising the following steps, implemented for a current block:
• decoding coefficients of the current block from the coded data read in the bit stream;
• transforming the current block into a transformed decoded block, said current block comprising M row vectors and N column vectors, with M and N being non-zero integers, said transforming step implementing a first sub step to produce an intermediate block, that applies to the column vectors respectively row vectors of the current block, and a second substep to produce a block of pixels that applies to the row vectors respectively column vectors of the intermediate block, resulting from the first substep;
• rebuilding the image from the transformed decoded block;
• wherein:
• at least one of said first and second transformation substeps comprises, for a row vector respectively a column vector, called an input vector of the current block:
• forming a first subvector of size K<N respectively M from adjacent elements of the input vector and at least one second subvector of size equal to N−K or M−K respectively from adjacent elements of the input vector, not included in the first sub-vector, such that the sum of the sizes of the formed subvectors is equal to the size of the input vector;
• transforming the first subvector into a first transformed subvector by applying a first partial subtransform of size K×K and transforming the second subvector into a second transformed subvector by applying a second subtransform of size (N−K)×(N−K);
• and
• building a transformed input vector of the intermediate block for the first transformation substep, respectively of the transformed decoded block for the second transformation step, by inserting the first transformed subvector and the at least one second transformed subvector.

A non-transitory computer-readable medium comprising a computer program stored thereon, which comprises instructions for implementing an encoding method when executed by a processor of an encoding device, wherein the method comprises:

• encoding at least one digital image, said image being divided into a plurality of blocks of pixels processed in a defined order, said encoding comprising the following steps, implemented for a current block of predetermined dimensions:
• transforming the current block into a transformed block, said current block comprising M row vectors and N column vectors, with M and N being non-zero integers, said transforming comprising a first substep of transformation of the M row vectors, respectively column vectors, to provide an intermediate block formed from the transformed row vectors, respectively column vectors, and a second substep of transformation of the N column vectors, respectively row vectors of the intermediate block;
• encoding the transformed block to produce coded data representative of the transformed block;
• inserting the coded data into a bit stream representative of the coded image;
• and
• transmitting the bit stream over a communication network;
• wherein
• at least one of said first and second transformation sub-steps comprises, for a row vector respectively a column vector, called an input vector:
• forming a first subvector of size K<N respectively N from adjacent elements of the input vector and at least one second subvector of size equal to N−K respectively M−K respectively from adjacent elements of the input vector, not included in the first sub-vector, such that the sum of the sizes of the formed subvectors is equal to the size of the input vector;
• transforming the first subvector into a first transformed subvector by applying a first partial subtransform of size K×K and transforming the second subvector into a second transformed subvector by applying a second subtransform of size (N−K)×(N−K);
• and
• building a transformed row vector respectively a transformed column vector of the intermediate block for the first transformation substep, respectively of the decoded block transformed for the second transformation step, by inserting the first transformed subvector and the at least one second transformed subvector.