High precision 4x4 dst7 and dct8 transform matrices

A method comprising:

• applying a transform to a block of residual samples using a first matrix of integer coefficients representative of the transform, the first matrix of integer coefficients being derived from a second matrix of integer coefficients, absolute values of the integer coefficients of the second matrix taking their values in a set of at least three values, the derivation comprising a modification of one value of the set such that a sum of two values of the set equals a third value of the set, and the sum of the two values being different from the third value before the modification.

A device for reconstructing a block of a picture comprising an electronic circuitry adapted for:

• applying an inverse transform to a block of transform coefficients using a first matrix of integer coefficients representative of the inverse transform, wherein the first matrix of integer coefficients is an inverse of a second matrix of integer coefficients representative of a transform inverted to obtain the inverse transform, the second matrix of integer coefficients being derived from a third matrix of integer coefficients, absolute values of the integer coefficients of the third matrix taking their values in a set of at least three values, the derivation comprising a modification of one value of the set such that a sum of two values of the set equals a third value of the set, and the sum of the two values being different from the third value before the modification.

A device for encoding a block of a picture comprising an electronic circuitry adapted for:

• applying a transform to a block of residual samples using a first matrix of integer coefficients representative of the transform, the first matrix of integer coefficients being derived from a second matrix of integer coefficients, absolute values of the integer coefficients of the second matrix taking their values in a set of at least three values, the derivation comprising a modification of one value of the set such that a sum of two values of the set equals a third value of the set, and the sum of the two values being different from the third value before the modification.

13-14. (canceled)