Method, medium, and system compensating shadow areas

• US 20080025635A1
• Filed: 07/09/2007
• Published: 01/31/2008
• Est. Priority Date: 07/31/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Seung-Sin, Han, Young-ran, Park, Du-sik
• Granted Patent: US 8,155,474 B2
• Time in Patent Office: Days
• US Class Current: 382/274
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: G06T 7/38 Registration of image sequences
• CPC Class Codes: H04N 1/4072 dependent on the contents of the original

Abstract

An image compensating system, medium, and method, including, a shadow area compensating system, medium, and method which may significantly increase the luminance of each pixel in a dark area with respect to pixels positioned in the vicinity of the corresponding pixel and slightly increase the luminance of each pixel in a bright area. The shadow area compensating method includes calculating a representative luminance Lav of each pixel having image information by reflecting the luminance of the corresponding pixel and the luminances of pixels positioned in the vicinity of the corresponding pixel, determining a compensation luminance ratio using the calculated representative luminance, and increasing an output luminance on the basis of the compensation luminance ratio.

Claims

1. An image compensating method, comprising:

calculating a representative luminance for each pixel of an image based on a luminance of a corresponding pixel and luminances of pixels positioned in a vicinity of the corresponding pixel;

determining a compensation luminance ratio using the calculated representative luminance; and

increasing an output luminance of at least the corresponding pixel based on the compensation luminance ratio,

wherein, the compensation luminance ratio decreases as the representative luminance increases.

2. The method of claim 1, further comprising dividing the image into a plurality of regions, calculating an average luminance for each of the divided regions, and determining whether a region, of the divided regions, has an average luminance lower than a threshold luminance.

3. The method of claim 1, wherein, when calculating the representative luminance, the representative luminance is calculated by averaging the luminances of the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel or by assigning weights, reflecting respective distances between the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel, to luminances of respective pixels positioned in the vicinity of the corresponding pixel and averaging corresponding weighted luminances.

4. The method of claim 1, wherein, when calculating the representative luminance, the representative luminance is calculated by calculating luminance differences between the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel, classifying the luminance differences into two groups according to whether each luminance difference is greater than a threshold luminance, and averaging luminances of pixels in a group, of the two groups, having a greatest number of pixels.

5. The method of claim 1, wherein when determining the compensation luminance ratio, the compensation luminance ratio is represented by I_{N(x, y)}/Y and determined by the following Equation using the representative luminance as represented by L_av:

$Y=\left(\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{av}}}+1}\right)<br><br>\left(1-\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{av}}}+1}\right)+I_{N<br><br>\left(x,y\right)}^2,$

where if (Y>

I_{N(x, y)}) then Y=I_{N(x, y)}), I_{N(x, y)} is a normalized value of a luminance of a pixel positioned at coordinates (x, y) of an input image, I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image, I′

is a luminance of the pixel as output, and Y is an improved luminance ratio.

6. The method of claim 5, wherein when increasing an output luminance, the output luminance I′

is determined by the following Equation using the compensation luminance ratio;

$I^{\mathrm{\prime <br><br>}}=\frac{I_{N<br><br>\left(x,y\right)}}{Y}·<br><br>I_{\left(x,y\right)},$

where I_{N(x, y)} is the normalized value of the luminance of the pixel positioned at the coordinates (x, y) of the input image, and I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image.

7. The method of claim 1, further comprising:

receiving image information including luminance information for at least the corresponding pixel and a luminance of a pixel positioned in the vicinity of the corresponding pixel; and

outputting through an output unit an output image with at least the increased output luminance of at least the corresponding pixel.

8. At least one medium comprising computer readable code to control at least one processing element to implement the method of claim 1.

9. An image compensating method, comprising:

calculating a representative luminance for each pixel of an image based on a luminance of a corresponding pixel and luminances of pixels positioned in a vicinity of the corresponding pixel;

calculating an adaptive luminance by correlating the representative luminance with an exponential curve;

determining a compensation luminance ratio using the calculated adaptive luminance; and

increasing an output luminance of at least the corresponding pixel based on the compensation luminance ratio,

wherein, the compensation luminance ratio decreases as the representative luminance increases.

10. The method of claim 9, further comprising dividing the image into a plurality of regions, calculating an average luminance for each of the divided regions, and determining whether a region, of the divided regions, has an average luminance lower than a threshold luminance.

11. The method of claim 9, wherein when calculating the adaptive luminance, and with the representative luminance being represented by L_av, the adaptive luminance is represented by L_ad and is calculated by forming the exponential curve using the following Equation using T- and G-parameters:

$\mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(L_{\mathrm{av}}<<br><br>T\right)$ $L_{\mathrm{ad}}={\left(\frac{L_{\mathrm{av}}}{T-1}\right)}^G<br><br>\left(T-1\right),<br><br>\mathrm{else}$ $L_{\mathrm{ad}}=L_{\mathrm{av}}$

with the T-parameter being a maximum value of luminances to be shadow-corrected, and

with the G-parameter being an exponent for exponentiation with the representative luminance L_av as the base.

12. The method of claim 9, wherein the calculating of the adaptive luminance comprises classifying the image by creating a histogram of the image as a whole.

13. The method of claim 12, wherein the calculating of the adaptive luminance further comprises selecting T- and G-parameters corresponding to the classification of the image.

14. The method of claim 9, wherein when determining the compensation luminance ratio, and with the adaptive luminance being represented by Lad, the compensation luminance is represented by ratio I_{N(x, y)}/Y and is determined by the following Equation using the adaptive luminance L_ad:

$Y=\left(\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{ad}}}+1}\right)<br><br>\left(1-\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{ad}}}+1}\right)+I_{N<br><br>\left(x,y\right)}^2,$

where if (Y>

I_{N(x, y)}) then Y=I_{N(x, y)}), I_{N(x, y)} is a normalized value of a luminance of a pixel positioned at coordinates (x, y) of an input image, I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image, I′

is a luminance of the pixel as output, and Y is an improved luminance ratio.

15. The method of claim 14, wherein when increasing an output luminance, the output luminance I′

is determined by the following Equation using the compensation luminance ratio;

$I^{\mathrm{\prime <br><br>}}=\frac{I_{N<br><br>\left(x,y\right)}}{Y}·<br><br>I_{\left(x,y\right)},$

where I_{N(x, y)} is the normalized value of the luminance of the pixel positioned at the coordinates (x, y) of the input image, and I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image.

16. The method of claim 9, further comprising:

receiving image information including luminance information for at least the corresponding pixel and a luminance of a pixel positioned in the vicinity of the corresponding pixel; and

outputting through an output unit an output image with at least the increased output luminance of at least the corresponding pixel.

17. At least one medium comprising computer readable code to control at least one processing element to implement the method of claim 9.

18. An image compensating system, comprising:

a representative luminance calculating unit to calculate a representative luminance for each pixel of an image based on a luminance of a corresponding pixel and luminances of pixels positioned in a vicinity of the corresponding pixel;

a compensation luminance ratio determining unit to determine a compensation luminance ratio using the calculated representative luminance; and

a shadow compensating unit to increase an output luminance of at least the corresponding pixel based on the compensation luminance ratio,

wherein, the compensation luminance ratio decreases as the representative luminance is increases.

19. The system of claim 18, further comprising a spatial luminance analyzing unit to divide the image into a plurality of regions, calculate an average luminance for each of the divided regions, and determine whether a region, of the divided regions, has an average luminance lower than a threshold luminance.

20. The system of claim 18, wherein the representative luminance calculating unit calculates the representative luminance by averaging luminances of the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel or by assigning weights, reflecting respective distances between the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel, to luminances of respective pixels positioned in the vicinity of the corresponding pixel and averaging corresponding weighted luminances.

21. The system of claim 18, wherein the representative luminance calculates unit calculating the representative luminance by calculating luminance differences between the corresponding pixel and the pixels positioned in the vicinity of the corresponding pixel, classifying the luminance differences into two groups according to whether each luminance difference is greater than a threshold luminance or not, and averaging luminances of pixels in a group, of the two groups, having a greatest number of pixels.

22. The system of claim 18, wherein the compensation luminance ratio determining unit determines the compensation luminance ratio is represented by I_{N(x, y)}/Y and by the following Equation using the representative luminance as represented by L_av:

$Y=\left(\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{av}}}+1}\right)<br><br>\left(1-\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{av}}}+1}\right)+I_{N<br><br>\left(x,y\right)}^2,$

where if (Y>

I_{N(x, y)}) then Y=I_{N(x, y)}), I_{N(x, y)} is a normalized value of a luminance of a pixel positioned at coordinates (x, y) of an input image, I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image, I′

is a luminance of the pixel as output, and Y is an improved luminance ratio.

23. The system of claim 22, wherein the shadow compensating unit determines the output luminance I′

by the following Equation using the compensation luminance ratio;

$I^{\mathrm{\prime <br><br>}}=\frac{I_{N<br><br>\left(x,y\right)}}{Y}·<br><br>I_{\left(x,y\right)},$

where I_{N(x, y)} is the normalized value of the luminance of the pixel positioned at the coordinates (x, y) of the input image, and I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image.

24. The system of claim 18, further comprising:

an image input unit to receive image information including luminance information for at least the corresponding pixel and a luminance of a pixel positioned in the vicinity of the corresponding pixel; and

an image output unit to output an output image with at least the increased output luminance of at least the corresponding pixel.

25. An image compensating system, comprising:

a representative luminance calculating unit to calculate a representative luminance for each pixel of an image based on a luminance of a corresponding pixel and luminances of pixels positioned in a vicinity of the corresponding pixel;

an adaptive luminance calculating unit to calculate an adaptive luminance by correlating the representative luminance with an exponential curve;

a compensation luminance ratio determining unit to determine a compensation luminance ratio using the calculated adaptive luminance; and

a shadow compensating unit to increase an output luminance of at least the corresponding pixel based on the compensation luminance ratio,

wherein, the compensation luminance ratio decreases as the representative luminance increases.

26. The system of claim 25, further comprising a spatial luminance analyzing unit to divide an input image into a plurality of regions, calculate an average luminance for each of the divided regions, and determine whether a region, of the divided regions, has an average luminance lower than a threshold luminance.

27. The system of claim 25, wherein, with the representative luminance being represented by L_av, the adaptive luminance calculating unit calculates the adaptive luminance represented by L_ad by forming the exponential curve using the following Equation using T- and G-parameters:

$\mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(L_{\mathrm{av}}<<br><br>T\right)$ $\text{\hspace{1em}<br><br>}<br><br>L_{\mathrm{ad}}={\left(\frac{L_{\mathrm{av}}}{T-1}\right)}^G<br><br>\left(T-1\right)$ $\mathrm{else}$ $\text{\hspace{1em}<br><br>}<br><br>L_{\mathrm{ad}}=L_{\mathrm{av}},$

with the T-parameter being a maximum value of luminances to be shadow-corrected, and

with the G-parameter being an exponent for exponentiation with the representative luminance L_av as the base.

28. The system of claim 25, wherein the adaptive luminance calculating unit comprises a histogram analyzing unit to classify the image by creating a histogram of the image as a whole.

29. The system of claim 28, wherein the adaptive luminance calculating unit further comprises a parameter selecting unit selecting T- and G-parameters corresponding to the classification of the image.

30. The system of claim 25, wherein, with the adaptive luminance being represented by Lad, the compensation luminance ratio determining unit determines the compensation luminance ratio represented by I_{N(x, y)}/Y by the following Equation using the adaptive luminance L_ad:

$Y=\left(\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{ad}}}+1}\right)<br><br>\left(1-\frac{I_{N<br><br>\left(x,y\right)}}{\frac{I_{\left(x,y\right)}}{L_{\mathrm{ad}}}+1}\right)+I_{N<br><br>\left(x,y\right)}^2,$

where if (Y>

I_{N(x, y)}) then Y=I_N(x,y)), I_{N(x, y)} is a normalized value of a luminance of a pixel positioned at coordinates (x, y) of an input image, I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image, I′

is a luminance of the pixel as output, and Y is an improved luminance ratio.

31. The system of claim 30, wherein the shadow compensating unit determines the output luminance I′

by the following Equation using the compensation luminance ratio;

$I^{\mathrm{\prime <br><br>}}=\frac{I_{N<br><br>\left(x,y\right)}}{Y}·<br><br>I_{\left(x,y\right)},$

wherein I_{N(x, y)} is the normalized value of the luminance of the pixel positioned at the coordinates (x, y) of the input image, and I_{(x, y)} is the luminance of the pixel positioned at the coordinates (x, y) of the input image.

32. The system of claim 25, further comprising:

an image input unit to receive image information including luminance information for at least the corresponding pixel and a luminance of a pixel positioned in the vicinity of the corresponding pixel; and

an image output unit to output an output image with at least the increased output luminance of at least the corresponding pixel.