Display management for high dynamic range video

Patent metadata

Field	Value
Publication number	US-9961237-B2
Application number	US-201615544320-A
Country	US
Kind code	B2
Filing date	Jan 14, 2016
Priority date	Jan 19, 2015
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A display management processor receives an input image with enhanced dynamic range to be displayed on a target display which has a different dynamic range than a reference display. The input image is first transformed into a perceptually-quantized (PQ) color space, preferably the IPT-PQ color space. A color volume mapping function, which includes an adaptive tone-mapping function and an adaptive gamut mapping function, generates a mapped image. A detail-preservation step is applied to the intensity component of the mapped image to generate a final mapped image with a filtered tone-mapped intensity image. The final mapped image is then translated back to the display's preferred color space. Examples of the adaptive tone mapping and gamut mapping functions are provided.

First claim

The invention claimed is:

1. A method comprising:
accessing an input image in a first color space with a first dynamic range;
applying a color transformation step to the input image to determine a first output image in a perceptually-quantized IPT (IPT-PQ) color space, the first output image comprising intensity pixel values and chroma components pixel values, wherein the color transformation step comprises applying a non-linear perceptual quantizer function to a function of the input image;
applying a color-volume mapping function to the first output image to generate a tone-mapped output image, the tone-mapped output image comprising intensity pixel values and chroma components pixel values,
wherein the color-volume mapping function comprises a tone mapping function, a saturation mapping function, and a pixel saturation estimate function,
wherein the tone mapping function generates the intensity pixel values of the tone-mapped output image by applying a non-linear mapping to the intensity pixel values of the first output image,
wherein the saturation mapping function generates the chroma components pixel values of the tone-mapped output image by adjusting the chroma components pixel values of the first output image based on changes in intensity,
wherein the pixel saturation estimate function computes a saturation metric (S) as the sum of squares of the chroma components pixel values of the first output image, wherein the saturation metric is applied to the tone-mapped output image to darken bright saturated colors and to desaturate highly saturated colors, thereby modifying the intensity pixel values and the chroma components pixel values; and

applying a detail preservation function to the modified intensity pixel values of the tone-mapped output image to generate intensity pixel values of a filtered tone-mapped output image, the filtered tone-mapped output image comprising the modified chroma components pixel values of the tone-mapped output image.

2. The method of claim 1 , wherein applying the color transformation step further comprises:
removing any non-linear encoding from the input image to generate a linear image;
converting the linear image into an LMS color image; and
applying the non-linear perceptual quantizer (PQ) function to the LMS color image to generate the first output image.

3. The method of claim 2 , wherein the non-linear perceptual quantizer function comprises the SMPTE ST 2084 mapping function.

4. The method of claim 1 , wherein the tone-mapping function is expressed as a parameterized sigmoidal tone curve function, wherein parameters of the function are determined based on characteristics of a source display and a target display.

5. The method of claim 4 , wherein the characteristics of the source display comprise a minimum brightness value and a maximum brightness value for the source display.

6. The method of claim 4 , wherein the characteristics of the target display comprise a minimum brightness value and a maximum brightness value for the target display.

7. The method of claim 4 , wherein the characteristics of the source display are accessed through received source display metadata.

8. The method of claim 4 , wherein the sigmoidal tone function is expressed as

I
m

=

(

C
1

+

C
2

⁢

I
o
Slope

1
+

C
3

⁢

I
o
Slope

)

Rolloff

wherein C 1 , C 2 , C 3 , Slope, and Rolloff are constants defining the parameters of the tone-mapping function, and for an input I o , represented by an intensity pixel value of the first output image, I m is a corresponding output value, represented by the corresponding intensity pixel value of the tone-mapped output image.

9. The method of claim 4 , wherein parameters of the tone-mapping function are further determined based on a Brightness value and a Contrast value to adjust overall brightness and contrast of the tone-mapped output image.

10. The method of claim 1 , wherein the saturation mapping function is expressed as
ƒ SM ( I o )= I m −I o +1

wherein I m denotes the output of the tone-mapping function, and I o denotes the intensity pixel values of the first output image, and
wherein applying the color-volume mapping function comprises computing:
I m =ƒ T ( I o )*(1− S *α),

P m =P*ƒ SM ( I o )*(1− S *β),

T m =T*ƒ SM ( I o )*(1− S *β),

where S denotes the saturation metric generated by the pixel saturation estimation function, α and β denote input weights, ƒ T (I o ) denotes the tone-mapping function, ƒ SM (I o ) denotes the saturation mapping function, I o denotes the intensity pixel values of the first output image, P and T denote the chroma components pixel values of the first output image, I m denotes the pixel values of the tone-mapped output image, and P m and T m denote the color components pixel values of the tone-mapped output image.

11. The method of claim 10 , wherein the values of (1−S*α) and (1−S*β) are clamped to always be larger than zero.

12. The method of claim 1 , wherein applying the detail preservation function further comprises computing:
D=I o −I m ,
B=F ( D,H ),
Ex=F ( B,Hx ),
Ey=F ( B,Hy ),
E =(| Ex|+|Ey| )* W MSE +(1− W MS ),

I mƒ =I o −B−E *( D−B )
where F(D,H) denotes applying to image D a filter with kernel H, I o denotes intensity pixel values of the first output image, I m denotes the intensity pixel values of the tone-mapped output image, I mƒ denotes the intensity pixel values of the filtered tone-mapped output image, B denotes the output of a blur filter, Ex denotes the output of a horizontal edge-detection filter, Ey denotes the output of a vertical edge-detection filter, and W MSE and W MS are weights.

13. The method of claim 12 , wherein the E output value is further clamped to be between 0 and 1.

14. The method of claim 12 , wherein the kernel H comprises a 5×11 Gaussian filter with standard deviation equal to 2.

15. The method of claim 12 , wherein the kernel H comprises a low-pass filter.

16. An apparatus comprising a processor and configured to perform any one of the methods recited in claim 1 .

17. A non-transitory computer-readable storage medium having stored thereon computer-executable instruction for executing a method in accordance with claim 1 .

Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Atkins Robin

Classifications

• H04N9/646

  for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters · CPC title

• H04N1/6058 Primary

  Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut · CPC title

• H04N1/6005

  with luminance or chrominance signals, e.g. LC1C2, HSL or YUV · CPC title

• H04N9/68 Primary

  for controlling the amplitude of colour signals, e.g. automatic chroma control circuits (H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86) · CPC title

• H04N9/643

  Hue control means, e.g. flesh tone control · CPC title