Content-adaptive adjustments to tone mapping operations for high dynamic range content

1. A computer system comprising one or more processing units and memory, wherein the computer system implements a playback system that is to be connected to a target display device having a brightness level that is dynamically controllable by the playback system, and wherein the playback system includes:

decision logic implemented by software executable on one or more central processing units, among the one or more processing units, by software controlling special-purpose hardware, or by special-purpose hardware, wherein the decision logic is configured to:

receive histogram information for sample values of a picture of high dynamic range (“HDR”) content, wherein the histogram information for the sample values of the picture of HDR content is organized as multiple bins, each of the multiple bins having a count of the sample values of the picture of HDR content within that bin, and wherein each of the multiple bins represents a range of possible sample values between a minimum possible sample value for the bin and a maximum possible sample value for the bin;

set a tone mapping function based at least in part on the histogram information for the sample values of the picture of HDR content;

send, to the target display device, a control signal that indicates a brightness level of the target display device for display of the picture of HDR content; and

after tone mapping, send, to the target display device, the sample values of the picture of HDR content; and

a tone mapper configured to, as part of rendering the picture of HDR content for output to the target display device, apply tone mapping to input values for the sample values of the picture of HDR content, according to the tone mapping function, and thereby produce output values for the sample values of the picture of HDR content.

2. The computer system of claim 1 , wherein the multiple bins have variable size in terms of range of possible sample values in the multiple bins, respectively.

3. The computer system of claim 2 , wherein sizes of the multiple bins are perceptually weighted and define steps that are at least approximately uniform.

4. The computer system of claim 1 , wherein, to set the tone mapping function, the decision logic is configured to:

select a highest bin, among the multiple bins, satisfying a threshold count; and

set a maximum point of the tone mapping function based at least in part on the selected bin.

5. The computer system of claim 1 , wherein, to set the tone mapping function, the decision logic is configured to:

select the tone mapping function, from among multiple available tone mapping functions, based at least in part on the histogram information.

6. The computer system of claim 1 , wherein the decision logic is further configured to buffer parameters of the tone mapping function, wherein the parameters of the tone mapping function are paired with the sample values of the picture of HDR content and/or with encoded data for the picture of HDR content.

7. In a computer system that implements a playback system connected to a target display device having a brightness level that is dynamically controllable by the playback system, a method comprising:

producing sample values of a picture of high dynamic range (“HDR”) content;

generating, from the sample values of the picture of HDR content, histogram information for the sample values of the picture of HDR content, wherein the histogram information for the sample values of the picture of HDR content is organized as multiple bins, each of the multiple bins having a count of the sample values of the picture of HDR content within that bin, and wherein each of the multiple bins represents a range of possible sample values between a minimum possible sample value for the bin and a maximum possible sample value for the bin;

setting a tone mapping function based at least in part on the histogram information for the sample values of the picture of HDR content;

as part of rendering the picture of HDR content for output to the target display device, with a tone mapper, applying tone mapping to input values for the sample values of the picture of HDR content, according to the tone mapping function, and thereby producing output values for the sample values of the picture of HDR content;

sending, to the target display device, a control signal that indicates a brightness level of the target display device for display of the picture of HDR content; and

after the tone mapping, sending, to the target display device, the sample values of the picture of HDR content.

8. The method of claim 7 , wherein the setting the tone mapping function includes:

selecting the tone mapping function, from among multiple available tone mapping functions, based at least in part on the histogram information.

9. The method of claim 8 , wherein the multiple available tone mapping functions include a generic tone mapping function having first, second, and third segments, and wherein:

the first segment begins at a minimum point, ends at a first switch point, and maps input values along the first segment to output values along the first segment according to a first non-linear mapping;

the second segment begins at the first switch point, ends at a second switch point, and maps input values along the second segment to output values along the second segment according to a linear mapping; and

the third segment begins at the second switch point, ends at a maximum point, and maps input values along the third segment to output values along the third segment according to a second non-linear mapping.

10. The method of claim 9 , wherein the setting the tone mapping function further includes:

setting one or more of the first switch point and the second switch point based at least in part on the histogram information.

11. The method of claim 9 , wherein the second segment is configured such that the input values along the second segment are boosted by an offset according to the linear mapping, and wherein the setting the tone mapping function further includes setting the offset based at least in part on the histogram information.

12. The method of claim 8 , wherein the multiple available tone mapping functions include a dark-to-mid-range tone mapping function having first and second segments, and wherein:

the first segment begins at a minimum point, ends at a switch point, and maps input values along the first segment to output values along the first segment according to a non-linear mapping; and

the second segment begins at the switch point, ends at a maximum point, and maps input values along the second segment to output values along the second segment according to a linear mapping.

13. The method of claim 12 , wherein the dark-to-mid range tone mapping function is selected if a maximum sample value among the sample values of the picture of HDR content satisfies a threshold dark sample value but not a threshold bright sample value.

14. The method of claim 8 , wherein the multiple available tone mapping functions include a simplified tone mapping function that begins at a minimum point, ends at a maximum point, and maps input values along the simplified tone mapping function to output values along the simplified tone mapping function according to a linear mapping.

15. The method of claim 14 , wherein the simplified tone mapping function is selected if:

at least a threshold proportion of the sample values of the picture of HDR content are within a middle range of possible sample values;

a power-saving mode is active; and/or

a GPU-optimized mode is active.

16. The method of claim 8 , wherein the multiple available tone mapping functions include a dark-only tone mapping function that begins at a minimum point, ends at a maximum point, and maps input values along the dark-only tone mapping function to output values along the dark-only tone mapping function according to a non-linear mapping.

17. The method of claim 16 , wherein the dark-only tone mapping function is selected if a maximum sample value among the sample values of the picture of HDR content satisfies a threshold dark sample value.

18. One or more computer-readable media storing computer-executable instructions for causing a computer system, when programmed thereby, to perform operations, the computer system including a target display device having a brightness level that is dynamically controllable by the playback system, the operations comprising, for each of multiple pictures of high dynamic range (“HDR”) content in a video sequence:

decoding encoded data for the picture of HDR content, thereby producing sample values of the picture of HDR content;

generating histogram information for the sample values of the picture of HDR content, wherein the histogram information for the sample values of the picture of HDR content is organized as multiple bins, each of the multiple bins having a count of the sample values of the picture of HDR content within that bin, and wherein each of the multiple bins represents a range of possible sample values between a minimum possible sample value for the bin and a maximum possible sample value for the bin;

setting a tone mapping function based at least in part on the histogram information for the sample values of the picture of HDR content;

as part of rendering the picture of HDR content for output to the target display device, with a tone mapper, applying tone mapping to input values for the sample values of the picture of HDR content, according to the tone mapping function, and thereby producing output values for the sample values of the picture of HDR content;

sending, to the target display device, a control signal that indicates a brightness level of the target display device for display of the picture of HDR content; and

after the tone mapping, sending, to the target display device, the sample values of the picture of HDR content.

19. The or more computer-readable media of claim 18 , wherein the multiple bins have variable size in terms of range of possible sample values in the multiple bins, respectively.

20. The method of claim 7 , wherein the multiple bins have variable size in terms of range of possible sample values in the multiple bins, respectively.