Method and device for processing digital image, and computer-readable recording medium

1. A method of processing a digital image, comprising:

receiving a plurality of images;

converting the plurality of images into histograms;

setting a first of the plurality of images as a reference image;

setting a second of the plurality of images as a comparison target image;

generating an adjusted reference image based on the reference image and the comparison target image;

generating a masking image based on the adjusted reference image and the comparison target image;

generating an adjusted comparison target image by applying the masking image to the comparison target image; and

combining the reference image and the adjusted comparison target image to generate a high dynamic range (HDR) image.

2. The method of claim 1 , wherein generating the adjusted reference image comprises adjusting a distribution of the histogram of the reference image to be similar to a distribution of the histogram of the comparison target image.

3. The method of claim 2 , wherein generating the masking image comprises comparing a difference between the adjusted reference image and the comparison target image to produce a masking image.

4. The method of claim 3 , wherein the masking image is an image that represents a difference in brightness between the adjusted reference image and the comparison target image by comparing the adjusted reference image and the comparison target image for each pixel.

5. The method of claim 1 , wherein the plurality of images comprises a low exposure image obtained with a short exposure time and a high exposure image obtained with a long exposure time.

6. The method of claim 1 , wherein setting the reference image and setting the comparison target image comprises setting an image, in which pixels are relatively uniformly arranged from a dark area to a bright area on a histogram, as the reference image.

7. The method of claim 1 , wherein generating the HDR image comprises assigning a weight to the adjusted comparison target image and then combining the adjusted comparison target image with the reference image.

8. The method of claim 7 , wherein the weight is determined as a difference value of each pixel, which is obtained by comparing the adjusted reference image and the comparison target image on histograms and is normalized to be a value between 0 and 1.

9. The method of claim 8 , wherein the weight converges to 0 as the difference between the adjusted reference image and the comparison target image is the larger and the weight converges to 1 as the difference between the adjusted reference image and the comparison target image is the smaller.

10. The method of claim 1 , further comprising removing noise in the masking image.

11. The method of claim 10 , wherein removing the noise comprises processing an image by repeating at least once an erosion operation, a dilation operation and a smoothing operation.

12. An apparatus for processing a digital image, comprising:

one or more processors to execute:

an image obtaining unit to obtain a plurality of images;

a histogram conversion unit to convert the plurality of images into histograms;

an image classification unit to set a first of the plurality of images as a reference image and a second of the plurality of images as a comparison target image;

a histogram adjustment unit to adjust a distribution of the histogram based on the reference image and the comparison target image;

a masking image obtaining unit to generate a masking image based on the adjusted reference image and the comparison target image;

a comparison target image adjusting unit to apply the masking image to the comparison target image to generate an adjusted comparison target image; and

an HDR image synthesizing unit to combining the reference image and the adjusted comparison target image to generate an HDR image.

13. The method of claim 12 , wherein the histogram adjustment unit adjusts a distribution of the histogram of the reference image to be similar to a distribution of the histogram of the comparison target image.

14. The method of claim 12 , wherein the masking image obtaining unit compares a difference between the adjusted reference image and the comparison target image to produce a masking image.

15. The apparatus of claim 12 , wherein the plurality of images comprises a low exposure image obtained with a short exposure time and a high exposure image obtained with a long exposure time.

16. The apparatus of claim 12 , wherein the image classification unit sets an image, in which pixels are relatively uniformly arranged from a dark area to a bright area on a histogram, as the reference image.

17. The apparatus of claim 12 , wherein the masking image is an image which represents a difference in brightness between the adjusted reference image and the comparison target image by comparing the adjusted reference image and the comparison target image for each pixel.

18. The apparatus of claim 12 , wherein the comparison target image adjusting unit assigns a weight to the adjusted comparison target image and then combining the adjusted comparison target image with the reference image.

19. The apparatus of claim 18 , wherein the weight is determined as a difference value, which is obtained by comparing the adjusted reference image and the comparison target image on histograms and is normalized to be a value between 0 and 1.

20. The apparatus of claim 19 , wherein the weight converges to 0 as the difference between the adjusted reference image and the comparison target image is the larger and the weight converges to 1 as the difference between the adjusted reference image and the comparison target image is the smaller.

21. The apparatus of claim 12 , further comprising a noise removing unit configured to remove noise in the masking image.

22. The apparatus of claim 21 , wherein the noise removing unit processes an image by repeating at least once an erosion operation, a dilation operation and a smoothing operation.

23. A non-transitory computer-readable recording medium for recording a computer program having instructions, which when executed by a processor, cause the processor to:

receive a plurality of images;

convert the plurality of images into histograms;

set a first of the plurality of images as a reference image;

set a second of the plurality of images as a comparison target image;

generate an adjusted reference image based on the reference image and the comparison target image;

generate a masking image based on the adjusted reference image and the comparison target image;

generate an adjusted comparison target image by applying the masking image to the comparison target image; and

combine the reference image and the adjusted comparison target image to generate a high dynamic range (HDR) image.

24. The CRM of claim 23 , wherein the plurality of images comprises a low exposure image obtained with a short exposure time and a high exposure image obtained with a long exposure time.

25. The CRM of claim 23 , wherein the masking image is an image which represents a difference in brightness between the adjusted reference image and the comparison target image by comparing the adjusted reference image and the comparison target image for each pixel.

26. The CRM of claim 23 , wherein the weight is determined as a difference value of each pixel, which is obtained by comparing the adjusted reference image and the comparison target image on histograms and is normalized to be a value between 0 and 1.