METHODS AND DEVICES FOR ENCODING AND DECODING FRAMES WITH A HIGH DYNAMIC RANGE, AND CORRESPONDING SIGNAL AND COMPUTER PROGRAM

1 . A method for encoding a sequence of frames with a first dynamic range, comprising:

obtaining, for at least one frame with a first dynamic range of said sequence, at least one frame with a second dynamic range and at least one illumination map, said first dynamic range being higher than said second dynamic range,

embedding said at least one illumination map within said at least one frame with a second dynamic range, by:

obtaining, for at least one block of said at least one frame with a second dynamic range, selection parameters for selecting at least one bit of at least one information element obtained from said at least one block, said selection parameters comprising a threshold, a minimum value and a number of bits,

selecting, from said selection parameters:

at least one of said information element having a rank equal to, or above, said threshold and a value equal to, or above, said minimum value, to obtain at least one selected information element, and

at least one least significant bit of said at least one selected information element, to obtain at least one selected least significant bit, the number of selected least significant bit being inferior than, or equal to, said number of bits,

modifying said at least one selected least significant bit, to carry data representing at least a part of said at least one illumination map.

2 . The method according to claim 1 , wherein said at least one information element belongs to the group comprising:

transformed coefficients obtained from said at least one block,

filtering coefficients obtained from said at least one block,

offset values obtained from said at least one block.

3 . The method according to claim 1 , comprising encoding said at least one frame with a second dynamic range.

4 . The method according to claim 1 , comprising transmitting said selection parameters, or transmitting information representing said selection parameters and enabling their reconstruction by a decoder.

5 . The method according to claim 1 , wherein said information element is a DCT coefficient, and wherein said selecting selects the DCT coefficients having a rank higher than or equal to said threshold and a value higher than or equal to said minimum value, and wherein said modifying replaces the selected least significant bits by said data representing said at least one illumination map.

6 . The method according to claim 1 , wherein said information element is an offset value, and wherein said selecting selects the offset values with an index higher than or equal to said threshold and a value higher than or equal to said minimum value, and wherein said modifying replaces the selected least significant bits by said data representing said at least one illumination map.

7 . The method according to claim 1 , wherein said selection parameters are determined by:

determining initial selection parameters, and

implementing at least one iteration of refinement of the initial selection parameters.

8 . The method according to claim 1 , wherein said selection parameters or initial selection parameters are determined from a set of configuration frames and stored in at least one memory, and wherein obtaining selection parameters comprises reading said at least one memory.

9 . The method according to claim 1 , wherein said selection parameters are determined from a statistical study of said sequence of frames or of said set of configuration frames.

10 . A method for decoding a signal representing a sequence of frames with a first dynamic range, said signal comprising at least one frame with a second dynamic range carrying data representing at least a part of at least one illumination map, said first dynamic range being higher than said second dynamic range, said method comprising:

obtaining, for at least one block of said at least one frame with a second dynamic range, selection parameters for selecting at least one bit of at least one information element obtained from said at least one block, or information representing said selection parameters and enabling their reconstruction, said selection parameters comprising a threshold, a minimum value and a number of bits,

reconstructing said at least one illumination map from said selection parameters and said at least one frame with a second dynamic range, and

reconstructing at least one frame with a first dynamic range by combining said at least one illumination map with said at least one frame with a second dynamic range.

11 . The method according to claim 10 , wherein obtaining selection parameters, or information representing said selection parameters, comprises reading values stored in at least one memory.

12 . The method according to claim 10 , wherein obtaining selection parameters, or information representing said selection parameters, comprises extracting values transmitted in said signal.

13 . The method according to claim 10 , wherein reconstructing said at least one illumination map from said selection parameters and said at least one frame with a second dynamic range comprises:

selecting, from said selection parameters:

at least one of said information element having a rank equal to, or above, said threshold and a value equal to, or above, said minimum value, to obtain at least one selected information element, and

at least one least significant bit of said at least one selected information element, to obtain at least one selected least significant bit, the number of selected least significant bit being inferior than, or equal to, said number of bits,

extracting the values carried by said at least one selected least significant bit to reconstruct said at least one illumination map.

14 . A signal representing a sequence of frames with a first dynamic range, comprising at least one frame with a second dynamic range carrying data representing at least a part of at least one illumination map, said first dynamic range being higher than said second dynamic range,

wherein said signal carries, for at least one block of said at least one frame with a second dynamic range, selection parameters for selecting at least one at least one bit of at least one information element obtained from at least one block of said at least one frame with a second dynamic range, or information representing said selection parameters and enabling their reconstruction by a decoder, said selection parameters comprising a threshold, a minimum value and a number of bits.

15 . A computer program product downloadable from a communication network and/or recorded on a medium readable by computer and/or executable by a processor comprising program code instructions to execute the steps of a method according to claim 1 , when this program is executed on a computer.

16 . An encoder for encoding a sequence of frames with a first dynamic range, comprising at least one processor configured to:

obtain, for at least one frame with a first dynamic range of said sequence, at least one frame with a second dynamic range and at least one illumination map, said first dynamic range being higher than said second dynamic range,

embed said at least one illumination map within said at least one frame with a second dynamic range, by:

obtaining, for at least one block of said at least one frame with a second dynamic range, selection parameters for selecting at least one bit of at least one information element obtained from said at least one block, said selection parameters comprising a threshold (T), a minimum value and a number of bits,

selecting, from said selection parameters:

at least one of said information element, to obtain at least one selected information element having a rank equal to, or above, said threshold and a value equal to, or above, said minimum value, and

at least one least significant bit of said at least one selected information element, to obtain at least one selected least significant bit, the number of selected least significant bit being inferior than, or equal to, said number of bits,

modifying said at least one selected least significant bit, to carry data representing at least a part of said at least one illumination map.

17 . A decoder for decoding a signal representing a sequence of frames with a first dynamic range, said signal comprising at least one frame with a second dynamic range carrying data representing at least a part of at least one illumination map, said first dynamic range being higher than said second dynamic range

said decoder comprising at least one processor configured to:

obtain, for at least one block of said at least one frame with a second dynamic range, selection parameters for selecting at least one bit of at least one information element obtained from said at least one block of said at least one frame with a second dynamic range, or information representing said selection parameters and enabling their reconstruction, said selection parameters comprising a threshold, a minimum value and a number of bits,

reconstruct said at least one illumination map from said selection parameters and said at least one frame with a second dynamic range, and

reconstruct at least one frame with a first dynamic range by combining said at least one illumination map with said at least one frame with a second dynamic range.