Method for updating an encoder by filter interpolation

1. A method for updating a processing capacity of an encoder or decoder in order to use a modulated transform having a size greater than a predetermined size, said encoder or decoder being adapted to store an initial prototype filter defined by an ordered set of coefficients of an initial size, said method comprising:

constructing, using a computer processor, a prototype filter of a size greater than said initial size to implement the transform of a size greater than the predetermined size by inserting at least one coefficient between two consecutive coefficients of the initial prototype filter.

2. The method according to claim 1 , wherein the inserted coefficients are calculated from coefficients of the initial filter.

3. The method according to claim 1 , wherein the coefficient inserted between said two consecutive coefficients is calculated by weighting at least said two consecutive coefficients.

4. The method according to claim 3 , wherein the initial prototype filter satisfies a predetermined reconstruction relation, in which the weighting is done by way of at least one weighting function calculated from said reconstruction relation.

5. The method according to claim 4 , wherein the weighting function is calculated for each position of the coefficient inserted between the two consecutive coefficients.

6. The method according to claim 1 , wherein:

the size of the constructed filter h′ is U times greater than the size M of the initial filter h, where U and M are natural numbers strictly greater than one,

a shift value S is defined such that 0≦S<U, with S being a natural number, and

the constructed and initial filters satisfy the relation:

h ′( U×n+S )= h ( n ),

for any natural number n such that 0≦n<M.

7. The method according to claim 3 , wherein

the size of the constructed filter h′ is U times greater than the size M of the base filter h, where U and M are natural numbers strictly greater than one,

a shift value S is defined such that 0<S<U,

two weighting functions P δ and Q δ are defined for any natural number δ satisfying 0<δ<U,

the inserted coefficients are defined by the relation:

h ′( U×n+S +δ)= P δ ( n )× h ( n )+ Q δ ( n )× h ( n +1),

for any natural number n satisfying n<M.

8. A non-transitory computer program product comprising instructions for implementing the method according to claim 1 when said program is executed by a processor.

9. An encoder of digital signals, comprising:

at least two memory areas that include a first memory area for storing a first set of coefficients defining an initial prototype filter of a given size, and second memory area for storing a computer program comprising instructions for delivering a second set of coefficients determined from coefficients in the first set, with the set formed by inserting coefficients from the second set between two consecutive coefficients of the first set, defining a prototype filter of a size greater than that of the initial prototype filter; and

a device for implementing the method according to claim 3 for constructing the prototype filter of a size greater than that of the initial prototype filter.

10. A method of encoding by modulated transform, implemented by an encoder and comprising the steps of:

obtaining the size of a modulated transform to be used for the encoding,

if the size of the transform is greater than the size of an initial prototype filter stored in the encoder, updating the processing capacity of the encoder according to the method according to claim 1 ,

encoding the signal via said modulated transform, making use of the prototype filter constructed during the update.

11. The decoder of digital signals, comprising:

at least two memory areas that include a first memory area for storing a first set of coefficients defining an initial prototype filter of a given size, and a second memory area for storing a computer program comprising instructions for delivering a second set of coefficients determined from coefficients in the first set, with the set formed by inserting coefficients from the second set between two consecutive coefficients of the first set, defining a prototype filter of a size greater than that of the initial prototype filter; and

a device for implementing the method according to claim 3 for constructing the prototype filter of a size greater than that of the initial prototype filter.

12. A method of decoding by modulated transform, implemented by a decoder and comprising the steps of:

obtaining the size of a modulated transform to be carried out for the decoding,

if the size of the transform is greater than the size of an initial prototype filter stored in the decoder, updating the processing capacity of the decoder according to a method according to claim 1 ,

decoding the signal via said modulated transform, making use of the prototype filter constructed during the update.

13. An encoder of digital signals, comprising:

at least two memory areas that include a first memory area for storing a first set of coefficients defining an initial prototype filter of a given size, and second memory area for storing a computer program comprising instructions for delivering a second set of coefficients determined from coefficients in the first set, with the set formed by inserting coefficients from the second set between two consecutive coefficients of the first set, defining a prototype filter of a size greater than that of the initial prototype filter.

14. A decoder of digital signals, comprising:

at least two memory areas that include a first memory area for storing a first set of coefficients defining an initial prototype filter of a given size, and a second memory area for storing a computer program comprising instructions for delivering a second set of coefficients determined from coefficients in the first set, with the set formed by inserting coefficients from the second set between two consecutive coefficients of the first set, defining a prototype filter of a size greater than that of the initial prototype filter.