Digital image processing method and device for lightening said image

1. A computer-implemented method of processing a digital image, said image comprising a plurality of pixels, the method comprising:

computing a histogram of a distribution of the number of pixels of the image as a function of their luminance;

subdividing the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold, and into a second set of pixels having luminance values greater than the high threshold;

performing a first luminance processing operation on the first set of pixels that comprises increasing the luminance of the first set of pixels; and

performing a different second luminance processing operation on the second set of pixels;

wherein the method is implemented by a computer.

2. The computer-implemented method of claim 1 , wherein the first luminance processing operation further comprises a gamma-type transfer function processing operation having an adaptable gamma parameter that is applied to the first set of pixels.

3. The computer-implemented method of claim 1 , wherein the second luminance processing operation comprises an equalization of the histogram applied to the second set of pixels.

4. The computer-implemented method of claim 1 , wherein the second set of pixels have luminance values between the high threshold and a maximum threshold, and wherein said computing a histogram comprises:

computing an initial histogram;

determining a luminance range above and below which the values of the initial histogram are nil; and

redistributing the pixels in the luminance range between said low threshold and said maximum threshold so as to compute said histogram.

5. The computer-implemented method of claim 4 , further comprising:

wherein determining a luminance range above and below which the values of the initial histogram are nil comprises:

determining a first area between the bottom limit of the luminance range and an initial threshold; and

determining a second area between said initial threshold and the top limit of the luminance range; and

wherein redistributing the pixels in the luminance range between said low threshold and said maximum threshold comprises:

performing a first redistribution of the pixels in the first area in the range between the low threshold and the high threshold; and

performing a second redistribution of the pixels in the second area in the range between the high threshold and the maximum threshold so as to compute said histogram.

6. The computer-implemented method of claim 1 , further comprising:

enhancing some of the colors of the image by amplifying the chrominance of each pixel of the image according to a ratio between the lightened luminance and the original luminance of said pixel of the image.

7. The computer-implemented method of claim 1 , wherein the method is repeatedly performed to process a plurality of successive digital images of a video sequence, and wherein said high threshold has a constant value for each processing operation on the successive digital images.

8. A device for processing and lightening a digital image comprising a plurality of pixels, the device comprising at least one logic circuit or a microprocessor that is configured to:

compute a histogram of the distribution of the number of pixels of the image as a function of their luminance;

subdivide the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold and into a second set of pixels having luminance values greater than the high threshold;

perform a first luminance processing operation on the pixels of the first set of pixels, the first processing operation comprising an increase in the luminance of the pixels of the first set; and

perform a different second luminance processing operation on the pixels of the second set of pixels.

9. The device of claim 8 , wherein the first luminance processing operation comprises a gamma-type transfer function processing operation having an adaptable gamma parameter applied to the first set of pixels.

10. The device of claim 8 , wherein the second luminance processing operation comprises an equalization of the histogram applied to the second set of pixels.

11. The device of claim 8 , wherein the second set of pixels have luminance values between the high threshold and a maximum threshold, and wherein to compute the histogram, the at least one logic circuit or microprocessor is configured to:

compute an initial histogram;

determine a luminance range above and below which the values of the initial histogram are nil; and

redistribute the pixels in the luminance range between said low threshold and said maximum threshold so as to compute said histogram.

12. The device of claim 11 , further comprising:

wherein to determine the luminance range above and below which the values of the initial histogram are nil, the at least one logic circuit or microprocessor is configured to:

determine a first area between the bottom limit of the luminance range and an initial threshold; and

determine a second area between said initial threshold and the top limit of the luminance range; and

wherein to redistribute the pixels in the luminance range between said low threshold and said maximum threshold, the at least one logic circuit or microprocessor is configured to:

perform a first redistribution of the pixels of the first area in the range between the low threshold and the high threshold; and

perform a second redistribution of the number of pixels of the second area in the range between the high threshold and the maximum threshold so as to compute said histogram.

13. The device of claim 8 , wherein the at least one logic circuit or microprocessor is further configured to:

enhance some of the colors of the image to amplify the chrominance of each pixel of the image according to a ratio between the lightened luminance and the original luminance of said pixel of the image.

14. The device of claim 8 , wherein the at least one logic circuit or microprocessor is further configured to process and lighten a plurality of successive digital images of a video sequence, wherein each of the plurality of successive digital images has a constant high threshold value.

15. A wireless communication appliance comprising a digital image processing device for processing and lightening a digital image comprising a plurality of pixels, the device including at least one logic circuit or a microprocessor that is configured to:

compute a histogram of the distribution of the number of pixels of the image as a function of their luminance;

subdivide the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold and into a second set of pixels having luminance values greater than the high threshold;

perform a first luminance processing operation on the pixels of the first set of pixels, the first processing operation comprising an increase in the luminance of the pixels of the first set; and

perform a different second luminance processing operation on the pixels of the second set of pixels.

16. A computer-implemented method of processing a digital image, said image comprising a plurality of pixels, the method comprising:

computing a histogram of a distribution of the number of pixels of the image as a function of their luminance;

subdividing the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold, and into a second set of pixels having luminance values greater than the high threshold;

performing a first luminance processing operation on the first set of pixels, the first luminance processing operation comprising a gamma-type transfer function processing operation having an adaptable gamma parameter applied to the first set of pixels for increasing the luminance of the first set of pixels; and

performing a different, second luminance processing operation on the second set of pixels, the second luminance processing operation comprising an equalization of the histogram applied to the second set of pixels;

wherein the method is implemented by a computer.

17. The computer-implemented method of claim 16 , wherein the pixels of the second set have luminance values between the high threshold and a maximum threshold, and wherein said computing a histogram comprises:

computing an initial histogram;

determining a luminance range above and below which the values of the initial histogram are nil; and

redistributing the pixels in the luminance range between said low threshold and said maximum threshold so as to compute said histogram.

18. The computer-implemented method of claim 17 , further comprising:

wherein determining a luminance range above and below which the values of the initial histogram are nil comprises:

determining a first area between the bottom limit of the luminance range and an initial threshold; and

determining a second area between said initial threshold and the top limit of the luminance range;

wherein redistributing the pixels in the luminance range between said low threshold and said maximum threshold comprises:

performing a first redistribution of the pixels in the first area in the range between the low threshold and the high threshold; and

performing a second redistribution of the pixels in the second area in the range between the high threshold and the maximum threshold so as to compute said histogram.

19. The method of claim 16 , further comprising:

enhancing some of the colors of the image by amplifying the chrominance of each pixel of the image according to a ratio between the lightened luminance and the original luminance of said pixel of the image.

20. The method of claim 16 , wherein the method is repeatedly performed to process a plurality of successive digital images of a video sequence, and wherein said high threshold has a constant value for each processing operation on the successive digital images.

21. A device for processing and lightening a digital image comprising a plurality of pixels, the device comprising at least one logic circuit or a microprocessor that is configured to:

compute a histogram of the distribution of the number of pixels of the image as a function of their luminance;

subdivide the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold and into a second set of pixels having luminance values greater than the high threshold;

perform a first luminance processing operation on the first set of pixels, the first luminance processing operating comprising a gamma-type transfer function processing operation having an adaptable gamma parameter applied to the first set of pixels for increasing the luminance of the first set of pixels; and

perform a different, second luminance processing operation on the second set of pixels, the second luminance processing operation comprising an equalization of the histogram applied to the second set of pixels.

22. The device of claim 21 , wherein the second set of pixels have luminance values between the high threshold and a maximum threshold, and wherein to compute the histogram, the at least one logic circuit or microprocessor is configured to:

compute an initial histogram;

determine a luminance range above and below which the values of the initial histogram are nil; and

redistribute the pixels in the luminance range between said low threshold and said maximum threshold so as to compute said histogram.

23. The device of claim 22 , further comprising:

wherein to determine the luminance range above and below which the values of the initial histogram are nil, the at least one logic circuit or microprocessor is configured to:

determine a first area between the bottom limit of the luminance range and an initial threshold; and

determine a second area between said initial threshold and the top limit of the luminance range; and

wherein to redistribute the pixels in the luminance range between said low threshold and said maximum threshold, the at least one logic circuit or microprocessor is configured to:

perform a first redistribution of the pixels of the first area in the range between said low threshold and said high threshold; and

perform a second redistribution of the number of pixels of the second area in the range between said high threshold and the maximum threshold so as to compute said histogram.

24. The device of claim 21 , wherein the at least one logic circuit or microprocessor is further configured to:

enhance some of the colors of the image to amplify the chrominance of each pixel of the image according to a ratio between the lightened luminance and the original luminance of said pixel of the image.

25. The device of claim 21 , wherein the at least one logic circuit or microprocessor is further configured to process and lighten a plurality of successive digital images of a video sequence, wherein each of the plurality of successive digital images has a constant high threshold value.

26. A wireless communication appliance comprising a digital image processing device for processing and lightening a digital image comprising a plurality of pixels, the device including at least one logic circuit or a microprocessor that is configured to:

compute a histogram of the distribution of the number of pixels of the image as a function of their luminance;

subdivide the pixels of the image into a first set of pixels having luminance values between a low threshold and a high threshold and into a second set of pixels having luminance values greater than the high threshold;

perform a first luminance processing operation on the first set of pixels, the first luminance processing operating comprising a gamma-type transfer function processing operation having an adaptable gamma parameter applied to the first set of pixels for increasing the luminance of the first set of pixels; and

perform a different, second luminance processing operation on the second set of pixels, the second luminance processing operation comprising an equalization of the histogram applied to the second set of pixels.