A METHOD AND APPARATUS FOR INVERSE-TONE MAPPING A PICTURE

1 - 22 . (canceled)

23 . A method for inverse-tone mapping colors of a color picture, comprising, for each of said colors:

obtaining a first component (Y) of said color comprising:

obtaining a luminance component (L) from said color and a modulation value (Ba) representative of the brightness of said color picture;

applying a non-linear function on said luminance component (L) resulting in a resulting component in order that the dynamic of the resulting component is increased compared to the dynamic of the luminance component (L)

multiplying said resulting component by said modulation value (Ba), resulting in said first component (Y);

then:

obtaining two chrominance components (C1, C2) from said color;

dividing each chrominance component (C1, C2) by a value equal to the square root of a first factor (r(L(i))), resulting in two intermediate chrominance components (C′1, C′2), wherein said first factor (r(L)) depends on a value (L(i)) of said luminance component (L);

obtaining three color components (Ec) comprising:

combining together the two intermediate chrominance components (C′1, C′2) and the first component (Y), resulting in a second component (S);

linearly combining together the two intermediate chrominance components (C′1, C′2) and said second component (S), resulting in at least one intermediate color component (Dc); and

taking the square of each intermediate color components (Dc), resulting in said three color components (Ec) and

forming an inverse-tone mapped color by combining together said three color components (Ec).

24 . The method of claim 23 , wherein the non-linear function is the inverse of either a gamma curve or a Slog curve according to value of said luminance component (Y).

25 . The method of claim 23 , wherein the method further comprises obtaining at least one of the following values from either a local or remote memory and/or from a bitstream:

the modulation value (Ba);

parameters of the non-linear function;

an information data (Inf) that indicates whether either the non-linear function is a gamma correction or a Slog correction.

26 . The method of claim 23 , wherein said first factor (r(L(i)) is a ratio of the value (L(i)) of the pixel (i) of said luminance component over the luminance value (Y(i)) of the co-located pixel (i) in said first component (Y).

27 . The method of claim 23 , wherein said first factor (r(I(i))) is obtained from either a local or remote memory or from a bitstream.

28 . A method for inverse-tone mapping colors of a color picture, comprising, for each of said colors:

obtaining an input luminance component (L″) and two input chrominance components (C″1, C″2) from said color;

obtaining a modulation value (Ba) from the value of each pixel (i) of said luminance component (L);

determining a second factor (β(Ba,L(i))) from said modulation value (Ba);

obtaining a luminance component (L) by linearly combining together said input luminance component (L″) and said two input chrominance components (C″1, C″2) and said two chrominance components (C1, C2) by multiplying each of said two input chrominance components (C″1, C″2) by said second factor (β(Ba,L(i))) as follows:

{

L

=

L

″

+

mC

1

″

+

nC

2

″

C

1

=

β

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(

Ba

,

L

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(

i

)

)

*

C

1

″

C

2

=

β

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(

Ba

,

L

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(

i

)

)

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C

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″

where L″ is the input luminance component, C 1 ″ and C 2 ″ are the two input chrominance components, L is the luminance component, C 1 and C 2 are the two chrominance components, Ba is the modulation value, m and n are coefficients, β(Ba,L(i)) is said second factor.

29 . The method of claim 28 , wherein the values of the luminance component (L) is given by:

L=L ″+max(0, mC 1 ′+nC 2 ′)

30 . The method of claim 29 , wherein the second factor (β(Ba,L(i))) is obtained by minimizing a gamut distorsion calculated between a targeted gamut (G1) and the gamut (G2) of the picture to be inverse tone-mapped.

31 . A device for inverse-tone mapping a picture, comprising a processor configured to:

applying, on a luminance component (L) obtained from the picture, a non-linear function that depends on an obtained modulation value (Ba), resulting in a resulting component in order that the dynamic of the first component is increased compared to the dynamic of the luminance component,

multiplying said resulting component by said modulation value (Ba), resulting in a first (expanded luminance) component (Y),

obtaining two chrominance components (C1, C2) from said color;

dividing each chrominance component (C1, C2) by a value equal to the square root of a first (scaling) factor (r(L(i))), resulting in two intermediate chrominance components (C′1, C′2), wherein said first (scaling) factor (r(L)) depends on a value (L(i)) of said luminance component (L);

obtaining three color components (Ec) comprising:

combining together the two intermediate chrominance components (C′1, C′2) and the first luminance component (Y), resulting in a second component (S);

linearly combining together the two intermediate chrominance components (C′1, C′2) and said second component (S), resulting in at least one intermediate color component (Dc); and

taking the square of each intermediate color components (Dc), resulting in said three color components (Ec), and

forming an inverse-tone mapped color by combining together said three color components (Ec).

32 . A computer program product comprising program code instructions to execute the steps of the method according to claim 23 when this program is executed on a computer.