A method and apparatus for inverse-tone mapping a picture

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).

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
• 
• (
• Ba
• ,
• L
• 
• (
• i
• )
• )
• *
• C
• 1
• ″
• C
• 2
• =
• β
• 
• (
• Ba
• ,
• L
• 
• (
• i
• )
• )
• *
• C
• 2
• ″
• where L″ is the input luminance component, C1″ and C2″ are the two input chrominance components, L is the luminance component, C1 and C2 are the two chrominance components, Ba is the modulation value, m and n are coefficients, β(Ba,L(i)) is said second factor.

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).