Efficient Tone-Mapping Of High-Bit-Depth Video To Low-Bit-Depth Display

• US 20130241931A1
• Filed: 03/12/2013
• Published: 09/19/2013
• Est. Priority Date: 03/14/2012
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Nasiopoulos, Panos, Ward, Rabab K., Mai, Zicong
• Granted Patent: US 9,129,445 B2
• Time in Patent Office: Days
• US Class Current: 345/428
• CPC Class Codes: G06T 11/60 Editing figures and text; Combining figures or text
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/646 Transmitting or storing colour television type signals, e.g. PAL, Lab; Their conversion into additive or subtractive colour signals or vice versa therefor H04N1/642, H04N1/644 take precedence

Abstract

Several embodiments of an efficient tone mapping of high bit depth video to low bit depth displays are disclosed. In one embodiment, a system maps an input image data of a high dynamic range (HDR) onto output image data of a lower dynamic range (LDR) and where the mapping does not transform the input image data from one color space to another color space. One embodiment comprises a tone mapping module which outputs a tone-mapped luminance signal for output image data and a color mapping module which outputs chroma signals for the output image data. Intermediate image processing steps may be avoided and hence may increase the efficiency of the mapping.

Claims

1. A system for mapping an input image data of a first image data format, said first image data format comprising a first dynamic range, to an output image data of a second image data format, said second image data format comprising a second dynamic range, said second dynamic range comprising a lower dynamic range than said first dynamic image range, said system comprising:

a tone mapping module, said tone mapping module inputting the luminance signal from said input image data of said first image data format and outputting a tone-mapped luminance signal for output image data of said second image data format;

a color mapping module, said color mapping module inputting the chroma signal from said input image data of said first dynamic range and inputting said tone-mapped luminance signal from said tone mapping module, said tone-mapped luminance signal being associated with said chroma signal and said color mapping module outputting chroma signals for said output image data; and

wherein further said first image data format is the same as said second image data format.

2. The system as recited in claim 1 wherein said first image data format and said second data image format comprises one of a group, said group comprising YCbCr image data format and RGB image data format.

3. The system as recited in claim 2 wherein said first image data format comprises a HDR image format for an HDR image capture device.

4. The system as recited in claim 3 wherein said second image data format comprises a LDR image format for a LDR display device.

5. The system as recited in claim 4 wherein said color mapping module is capable of mapping the chroma channel comprising a function dependent upon (y′

, s, Γ

, γ

) where y′

comprises the tone mapped luminance signal, s comprises a saturation adjustment term, Γ

comprises the gamma value for said HDR image capture device, and γ

comprises the gamma value for said LDR display device.

6. The system as recited in claim 5 wherein said function comprises:

7. The system as recited in claim 6 wherein the parameters (M_b, m_b, M_R, m_r, T and t) of said function comprise values derived from image data standards.

8. The system as recited in claim 7 wherein said image data standards comprise one of a group, said group comprising:

ITU-R BT.601 and ITU-R BT.709 standards.

9. A method for mapping an input image data of a first image data format, said first image data format comprising a first dynamic range, to an output image data of a second image data format, said second image data format comprising a second dynamic range, said second dynamic range comprising a lower dynamic range than said first dynamic image range, the steps of said method comprising:

inputting said input image data, said input image data of a first image data format, said first image data format comprising a first dynamic range;

tone mapping said input image data, said tone mapping extracting a tone-mapped luminance signal from said input image data;

color mapping said input image data, said color mapping inputting said tone-mapped luminance signal and chroma signal from said input image data and outputting; and

outputting an output image data of a second image data format and wherein said second image data format is the same as said first image data format.

10. The method as recited in claim 9 wherein the step of tone mapping further comprises the step of inputting the luminance signal, Y′

, from input image data in YCbCr format.

11. The method as recited in claim 10 wherein the step of tone mapping further comprises the step of extracting the luminance signal from the input image data.

12. The method as recited in claim 9 wherein the step of color mapping further comprises the step of applying a function dependent upon (y′

, s, Γ

, γ

) where y′

comprises the tone mapped luminance signal, s comprises a saturation adjustment term, Γ

comprises the gamma value for said HDR image capture device, and y comprises the gamma value for said LDR display device.

13. The method as recited in claim 12 wherein said function comprises:

14. The method as recited in claim 13 wherein the parameters (M_b, m_b, M_R, m_r, T and t) of said function comprise values derived from image data standards.

15. The method as recited in claim 14 wherein said image data standards comprise one of a group, said group comprising:

ITU-R BT.601 and ITU-R BT.709 standards.