System and method of luminance processing in high dynamic range and standard dynamic range conversion
In some aspects, the disclosure is directed to methods and systems for transformation between media formats, such as between standard dynamic range (SDR) and high dynamic range (HDR) media or between HDR media formats, without undesired hue shifting, via one or both of a luminance mapping ratio technique and a direct color component mapping technique.
1. A method for converting between standard dynamic range (SDR) media and high dynamic range (HDR) media, comprising:
receiving, by a media processor, an input media item in a first format;
determining, by the media processor, a luminance mapping ratio between a pixel of the input media item in the first format and a corresponding pixel of the media item in a second format;
determining, by the media processor, a peak luminance scaling factor;
for each pixel of the media item in the first format:
for each color component value of the pixel:
calculating, by the media processor, an output value based on a product of the color component value of the pixel, the luminance mapping ratio, and the peak luminance scaling factor, and
replacing, by the media processor, the color component value of the pixel with the calculated output value in the second format; and
providing, by the media processor, the media item in the second format.
2. The method of claim 1 , wherein the first format is SDR media, and the second format is HDR media.
3. The method of claim 1 , wherein the luminance mapping ratio is greater than 1 for at least one pixel of the media item, prior to any renormalization of color component values.
4. The method of claim 1 , wherein determining the luminance mapping ratio further comprises retrieving the luminance mapping ratio, by the media processor, from a format conversion lookup table.
5. The method of claim 1 , wherein determining the luminance mapping ratio further comprises identifying the luminance mapping ratio, by the media processor, from a piecewise linear function.
6. The method of claim 1 , further comprising:
determining, by the media processor, a black level adjustment coefficient; and
wherein calculating the output value, for each color component value of the pixel, further comprises:
calculating, by the media processor, the output value comprising a sum of the black level adjustment coefficient and the product of the color component value of the pixel, the luminance mapping ratio, and the peak luminance scaling factor.
7. A method for converting between standard dynamic range (SDR) media and high dynamic range (HDR) media, comprising:
for each of a plurality of colors of a media item in a first format, retrieving, by a media processor of a device, a mapping factor from the first format to a second format, wherein the mapping factor varies based on the color component value of the pixel;
for each pixel of an item of input media in the first format:
for each color component value of the pixel:
calculating an output value, by the media processor, comprising a product of the color component value of the pixel and the mapping factor for the corresponding color.
8. The method of claim 7 , wherein retrieving the mapping factor comprises retrieving the mapping factor, by the media processor, from a format conversion lookup table.
9. The method of claim 7 , wherein retrieving the mapping factor comprises identifying the mapping factor, by the media processor, from a piecewise linear function.
10. A system for converting between standard dynamic range (SDR) media and high dynamic range (HDR) media, comprising:
a media processor of a device comprising an input and an output;
wherein the input is configured to receive an input media item in a first format;
wherein the media processor is configured to:
determine a luminance mapping ratio between a pixel of the input media item in the first format and a corresponding pixel of the media item in a second format,
determine a black level adjustment coefficient, and
for each pixel of the media item in the first format:
for each color component value of the pixel:
calculate an output value based on a sum of the black level adjustment coefficient and a product of the color component value of the pixel and the luminance mapping ratio, and
replace the color component value of the pixel with the calculated output value in the second format; and
wherein the output is configured to provide the media item in the second format.
11. The system of claim 10 , wherein the first format is SDR media, and the second format is HDR media.
12. The system of claim 11 , wherein the luminance mapping ratio is greater than 1.
13. The system of claim 10 , further comprising a memory unit of the device storing a format conversion lookup table; and wherein the media processor is further configured to retrieve the luminance mapping ratio from the format conversion lookup table.
14. The system of claim 10 , wherein the media processor is further configured to identify the luminance mapping ratio from a piecewise linear function.
15. The system of claim 10 , wherein the media processor is further configured to:
determine a peak luminance scaling factor; and
calculate the output value, for each color component value of the pixel, by:
calculating the output value based on the product of the color component value of the pixel, the luminance mapping ratio, and the peak luminance scaling factor.
16. The system of claim 10 , wherein the mapping factor varies based on the color component value of the pixel.