Method for processing a digital image, device, terminal equipment and associated computer program

A device comprising:

• a reprogrammable computing machine or a dedicated computing machine, capable of and configured to:
• receive at least one digital image, said image comprising image elements, an image element being associated with colour information represented in a first colour space comprising a first luminance component separated from chrominance components, said first luminance component having a first value comprised in a first predetermined value range;
• and
• process the at least one digital image for rendering the image on a display device, said display device being adapted to render second values of second luminance component of the images elements included in a second predetermined range of values, wherein the processing comprises:
• determining an information representative of a global luminosity level of the image, perceived by an observer, based on the values of the first luminance component of the elements of the image;
• calculating an expansion exponent as a function of the global luminosity level information determined;
• transforming the first luminance components of the image elements into said second luminance components, comprising for an element of the image, the calculation of an intermediate luminance value by applying the expansion exponent calculated to the first value of the first luminance component, the multiplication of the intermediate value calculated by a length of the second range of predetermined luminance values, and obtaining the second value of the second luminance component based on the multiplied intermediate luminance value,
• wherein the calculated expansion exponent is a decreasing function of the determined global luminosity level information, based on the logarithm of said determined global luminosity level information.

A non-transitory computer-readable storage medium, storing a computer program product comprising instructions, which when executed by a reprogrammable computing machine configure the computing machine to perform acts comprising:

• receiving at least one digital image, said image comprising image elements, an image element being associated with colour information represented in a first colour space comprising a first luminance component (Y1) and first chrominance components, said first luminance component having a first value within a first range of predetermined values;
• processing the at least one digital image for rendering on a display device, said display device being adapted to restore second values of second luminance component of the image elements included in a second range of predetermined values, wherein the processing comprises:
• determining an information representative of a global luminosity level of the image perceived by an observer, based on the values of the first luminance component of the elements of the image;
• calculating an expansion exponent (γ) as a function of the global luminosity level information determined;
• transforming the first luminance components of the image elements into said second luminance components, comprising for an element of the image, the calculation of an intermediate luminance value by applying the expansion exponent calculated to the first value of first luminance component, the multiplication of the calculated intermediate value by a length of the second range of predetermined luminance values, and obtaining the second value of the second luminance component based on the multiplied intermediate luminance value,
• wherein the calculated expansion exponent is a decreasing function of the determined global luminosity level information, based on the logarithm of said determined global luminosity level information.