SYSTEMS AND METHODS FOR LOCAL TONE MAPPING OF HIGH DYNAMIC RANGE IMAGES

• US 20110285737A1
• Filed: 05/20/2010
• Published: 11/24/2011
• Est. Priority Date: 05/20/2010
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Lin, Peng
• Granted Patent: US 8,766,999 B2
• Time in Patent Office: Days
• US Class Current: 345/589
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 5/10 Intensity circuits

Abstract

This is generally directed to systems and methods for local tone mapping of high dynamic range (“HDR”) images. For example, a HDR image can have its larger dynamic range mapped into the smaller dynamic range of a display device. In some embodiments, to perform the local tone mapping, a RGB to Y converter can be used to convert the input image signal to a luminance signal in the YCgCo color space, a shape adaptive filter can be used to separate the luminance signal into its illumination and reflectance components, contrast compression can be applied to the illumination component, image sharpening can be applied to the reflectance component, and the processed illumination and reflection components can be used to calculate a processed RGB signal. The dynamic range of the processed RGB signal can then be mapped into the dynamic range of the display device.

Claims

1. A method comprising:

calculating an illumination component of an input signal by processing the input signal with a shape adaptive filter;

processing the calculated illumination component to generate a processed illumination component in which a contrast of the input signal has been compressed;

processing the calculated illumination component to generate a processed reflectance component in which at least one feature of the input signal has been sharpened;

generating a processed input signal from the processed illumination component and the processed reflectance component, wherein the processed input signal comprises a contrast-compressed and image-sharpened version of the input signal; and

mapping the processed input signal into a dynamic range of a display device.

2. The method of claim 1, wherein the input signal compromises an image signal of a high dynamic range image.

3. The method of claim 1, wherein calculating the illumination component further comprises:

calculating the input signal'"'"'s associated luminance signal by transforming a red, green, and blue signal of the input signal into a YCgCo color space; and

processing the luminance signal with the shape adaptive filter to calculate the illumination component.

4. The method of claim 3, wherein the shape adaptive filter calculates the illumination component through the equation:

5. The method of claim 4, wherein w comprises one or more filter weights of the shape adaptive filter defined by:

6. The method of claim 5, wherein c1=1, c2=2, c3=3, and wherein σ

comprises a filter strength of the shape adaptive filter defined by;

7. The method of claim 1, wherein generating the processed input signal comprises:

multiplying the processed illumination component by the processed reflectance component to generate a processed luminance signal; and

transforming the processed luminance signal into a processed red, green, blue signal, wherein the processed red, green, blue signal comprises the processed input signal.

8. A system comprising:

a decomposer operable to receive a high dynamic range (“

HDR”

) image signal and decompose the image signal into at least an illumination component and a reflectance component;

a contrast compressor operable to receive the illumination component and compress the contrast of the image signal by processing the illumination component;

an image sharpener operable to receive the reflectance component and sharpen an image of the image signal by processing the reflectance component;

a multiplier operable to multiply the processed illumination component by the processed reflectance component to calculate a processed luminance signal;

a RGB processor operable to transform the processed luminance signal into its associated red, green, and blue signals; and

a range mapper operable to map a dynamic range of the associated red, green, and blue signals into a dynamic range of a display device.

9. The system of claim 8, wherein the decomposer comprises a shape adaptive filter.

10. The system of claim 8, further comprising:

RGB to Y converter operable to;

transform the HDR image signal from its associated red, green, and blue signals into at least a luminance signal; and

transmit the luminance signal to the decomposer for decomposing into the illumination component and the reflectance component.

11. The system of claim 10, wherein the decomposer is further operable to:

pass the luminance signal through a shape adaptive filter to calculate the luminance component; and

calculate the reflectance component by dividing the luminance signal by the luminance component.

12. The system of claim 8, wherein the display device comprises at least one of a computer monitor, a television, and a display of a laptop computer.

13. The system of claim 8, wherein the dynamic range of the display device is less than a dynamic range of the HDR image signal.

15. The system of claim 13, wherein the contrast compressor is further operable to:

execute a power function on the illumination component defined by;

16. The system of claim 15, wherein the contrast control parameters of the power function comprise the ranges:

0<

γ

_Low≦

1 and 0<

γ

_High<

1.5.

17. The system of claim 13, wherein the image sharpener is further operable to:

execute a noise coring function defined by;

18. The system of claim 17, wherein the variable of the log function comprise the range 0<

η

<

0.5.

19. The system of claim 13, wherein the range mapper is further operable to:

execute a standard gamma correction function of the display device on the processed image signal to map the dynamic range of the processed image signal into the dynamic range of the display device

20. The system of claim 13, wherein the input image comprises a high dynamic range image generated by an imaging device.

14. A system for performing local tone mapping of an input image, the system comprising:

a contrast compressor operable to receive and process an illumination component signal of the input image by;

executing a power function on the illumination component signal to generate an Lp signal; and

mapping a dynamic range of the Lp Signal into a dynamic range of the input image to generate a contrast-compressed signal;

an image sharpener operable to receive and process a reflectance component signal of the input image by;

executing a log function on the reflectance component signal to generate a Log(F) signal;

executing a noise coring function on the Log(F) signal to reduce magnification of noise, thereby generating a noise-cored signal; and

processing the received reflectance component signal and the noise-cored signal to generate a image-sharpened signal; and

a range mapper operable to;

generate a processed image signal from the contrast-compressed signal and the image-sharpened signal; and

map the dynamic range of the processed image signal into a dynamic range of a display device.