CN-121986495-A - Correcting SDR data in inverse tone mapping to improve HDR data in SL-HDR1 post-processing

Abstract

A method includes obtaining (40) picture data in a first dynamic range, determining (41) a first function allowing mapping of the picture data from the first dynamic range to a second dynamic range, signaling (42) metadata in video data, the metadata allowing obtaining a second function, the second function corresponding to an approximated version of the first function, determining (43) a third function from the first function and the second function such that applying the second function to intermediate data equivalent to applying the first function to the picture data in the first dynamic range, the intermediate data generated by applying the third function to the picture data in the first dynamic range, and signaling (44) data representing the intermediate data in the video data.

Inventors

• L. examination
• N. Calamelli
• P. Lopez
• D. Tuz

Assignees

• 交互数字CE专利控股有限公司

Dates

Publication Date

20260505

Application Date

20240927

Priority Date

20231010

Claims (17)

1. 1. A method, comprising: Obtaining (40) picture data in a first dynamic range; -determining (41) a first function allowing mapping of the picture data from the first dynamic range to a second dynamic range; Signaling (42) metadata in the video data, the metadata allowing to obtain a second function, the second function corresponding to an approximated version of the first function; determining (43) a third function from the first and second functions such that applying the second function to intermediate data is equivalent to applying the first function to the picture data in the first dynamic range, the intermediate data being generated by applying the third function to the picture data in the first dynamic range, and -Signaling (44) data representing the intermediate data in the video data.
2. 2. The method of claim 1, wherein a dynamic range of the first dynamic range is lower than a dynamic range of the second dynamic range.
3. 3. The method of claim 1 or 2, wherein the metadata represents an inverse of the first function.
4. 4. A method according to claim 1, 2 or 3, wherein the second function is the inverse of an intermediate function derived from the metadata.
5. 5. The method of claim 4, wherein the intermediate function is a tone mapping function represented by a first lookup table derived from the metadata, and the second function is an inverse tone mapping function represented by a second lookup table derived by inverting the intermediate function from the first lookup table.
6. 6. The method of claim 4 or 5, wherein the third function is derived from the intermediate function or from the second function.
7. 7. The method of any preceding claim, further comprising: obtaining (11231) a chrominance component from a current sample of the intermediate data using a color correction function; Estimating (11232) a clipping factor based on the obtained chrominance component and the precision value; Representing (11233) each obtained chrominance component as a product of a first sub-portion of a luminance component of the sample that depends on the intermediate data and a second sub-portion of a corresponding chrominance component of the sample that depends on the intermediate data, and obtaining a first ratio of a correction factor to be applied to the first sub-portion and a second ratio of the correction factor to be applied to the second sub-portion, the correction factor being based on the clipping factor; Obtaining (11234) luminance values of samples of corrected intermediate data corresponding to the samples of the intermediate data using the first subsection divided by a first ratio-wise power of the correction factor, and Obtaining (11235), for each chrominance component, a chrominance value of the sample of corrected intermediate data corresponding to the sample of intermediate data by dividing the second sub-portion of the chrominance component by a second ratio-wise power of the correction factor; wherein the data representing the intermediate data is the corrected intermediate data.
8. 8. A device comprising electronic circuitry configured to: Obtaining (40) picture data in a first dynamic range; -determining (41) a first function allowing mapping of the picture data from the first dynamic range to a second dynamic range; Signaling (42) metadata in the video data, the metadata allowing to obtain a second function, the second function corresponding to an approximated version of the first function; determining (43) a third function from the first and second functions such that applying the second function to intermediate data is equivalent to applying the first function to the picture data in the first dynamic range, the intermediate data being generated by applying the third function to the picture data in the first dynamic range, and -Signaling (44) data representing the intermediate data in the video data.
9. 9. The apparatus of claim 8, wherein a dynamic range of the first dynamic range is lower than a dynamic range of the second dynamic range.
10. 10. The apparatus of claim 8 or 9, wherein the metadata represents an inverse of the first function.
11. 11. The apparatus of claim 8, 9 or 10, wherein the second function is an inverse of an intermediate function derived from the metadata.
12. 12. The apparatus of claim 11, wherein the intermediate function is a tone mapping function represented by a first lookup table derived from the metadata, and the second function is an inverse tone mapping function represented by a second lookup table derived by inverting the intermediate function from the first lookup table.
13. 13. The apparatus of claim 11 or 12, wherein the third function is derived from the intermediate function or from the second function.
14. 14. The apparatus of any preceding claim 8 to 13, wherein the electronic circuitry is further configured to: obtaining (11231) a chrominance component from a current sample of the intermediate data using a color correction function; Estimating (11232) a clipping factor based on the obtained chrominance component and the precision value; Representing (11233) each obtained chrominance component as a product of a first sub-portion of a luminance component of the sample that depends on the intermediate data and a second sub-portion of a corresponding chrominance component of the sample that depends on the intermediate data, and obtaining a first ratio of a correction factor to be applied to the first sub-portion and a second ratio of the correction factor to be applied to the second sub-portion, the correction factor being based on the clipping factor; Obtaining (11234) luminance values of samples of corrected intermediate data corresponding to the samples of the intermediate data using the first subsection divided by a first ratio-wise power of the correction factor, and Obtaining (11235), for each chrominance component, a chrominance value of the sample of corrected intermediate data corresponding to the sample of intermediate data by dividing the second sub-portion of the chrominance component by a second ratio-wise power of the correction factor; wherein the data representing the intermediate data is the corrected intermediate data.
15. 15. A non-transitory information storage medium storing program code instructions for implementing the method of any preceding claim 1 to 7.
16. 16. A computer program comprising program code instructions for implementing the method of any preceding claim 1 to 7.
17. 17. A signal generated by the method of any one of the preceding claims 1 to 7 or by the apparatus of any one of the preceding claims 8 to 14.

Description

Correcting SDR data in inverse tone mapping to improve HDR data in SL-HDR1 post-processing Technical Field At least one of the present embodiments relates generally to the field of video generation, and more particularly to a method, apparatus, and system for improving HDR data in a SL-HDR1 system. Background Recent advances in display technology began to allow for extended dynamic range colors, brightness, and contrast in the displayed image. The term image refers herein to image content that may be, for example, video or still pictures or images. High dynamic range video (HDR video) describes video with a dynamic range that is greater than the dynamic range of standard dynamic range video (SDR video). HDR video involves capturing, generating (production), content/encoding, and displaying. HDR capture and display devices can have brighter white and darker black. To accommodate this, the HDR encoding standard allows for higher maximum brightness and uses at least a 10-bit dynamic range (as compared to non-professional 8-bit SDR video and professional 10-bit SDR video) in order to maintain accuracy over this extended range. HDR production is a new domain and there will be a transitional phase during which both HDR content and SDR content will coexist. During this coexistence phase, the same content will be produced simultaneously in both HDR and SDR versions. The user may then display an HDR or SDR version of the content according to their preferences or capabilities. One proposed solution for standard SL-HDR1 (ETSI TS 103 433-1 v1.4.1) consists in generating content in the form of SDR video and metadata. The metadata represents an inverse tone mapping curve that allows for transforming SDR video into HDR video. Thus, the standard SL-HDR1 proposes a single layer approach that avoids transmitting SDR and HDR versions of the same content to the user. In some cases, an inverse tone mapping curve is designed on the sender device to obtain the desired rendering quality of the HDR video. The metadata is then used to recreate the inverse tone mapping curve at the receiver side, which is used to generate HDR video from SDR video. However, the HDR video generated at the receiver side may be slightly different from the desired HDR video due to some quantization applied to the parameters representing the inverse tone mapping curve. It is desirable to overcome the above disadvantages. It is particularly desirable to propose a system that allows to obtain HDR video from metadata and SDR video that is as close as possible to the desired HDR video. Disclosure of Invention In a first aspect, one or more of the present embodiments provides a method comprising: Obtaining picture data in a first dynamic range; Determining a first function that allows mapping the picture data from the first dynamic range to a second dynamic range; Signaling metadata in video data, the metadata allowing to obtain a second function, the second function corresponding to an approximated version of the first function; Determining a third function from the first function and the second function such that applying the second function to intermediate data generated by applying the third function to the picture data in the first dynamic range is equivalent to applying the first function to the picture data in the first dynamic range, and Data representing the intermediate data is signaled in the video data. In an embodiment, the dynamic range of the first dynamic range is lower than the dynamic range of the second dynamic range. In an embodiment, the metadata represents an inverse of the first function. In an embodiment, the second function is an inverse of an intermediate function derived from the metadata. In an embodiment, the intermediate function is a tone mapping function represented by a first lookup table derived from metadata, and the second function is an inverse tone mapping function represented by a second lookup table derived by inverting the intermediate function from the first lookup table. In an embodiment, the third function is derived from the intermediate function or from the second function. In an embodiment, the method further comprises: obtaining a chrominance component from a current sample of the intermediate data using a color correction function; estimating a clipping factor based on the obtained chrominance component and the precision value; representing each obtained chrominance component as a product of a first sub-portion of a luminance component of the sample that depends on the intermediate data and a second sub-portion of a corresponding chrominance component of the sample that depends on the intermediate data, and obtaining a first ratio of a correction factor to be applied to the first sub-portion and a second ratio of the correction factor to be applied to the second sub-portion, the correction factor being based on the clipping factor; obtaining luminance values of samples of corrected intermediate data corresponding