Method and system for processing low-illuminance image

• US 20090180704A1
• Filed: 01/05/2009
• Published: 07/16/2009
• Est. Priority Date: 01/15/2008
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Oh, Hyun-Hwa, Lee, Seong-Deok, Yoo, Young-Jin, Wey, Ho-Cheon
• Granted Patent: US 8,295,629 B2
• Time in Patent Office: Days
• US Class Current: 382/254
• CPC Class Codes: G06T 2207/10144 Varying exposure
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction

Abstract

Provided are a method and system for processing a low-illuminance image. The system includes an image acquisition unit to acquire two images having different levels of illuminance and sensitivity as first and second images; a motion vector estimation unit to extract a motion vector of the second image based on the first image; an image correction unit to correct the second image using the extracted motion vector; a synthesis coefficient calculation unit to calculate a synthesis coefficient used to synthesize the first image and the corrected second image; and an image synthesis unit to synthesize the first image and the corrected second image using the calculated synthesis coefficient.

Claims

1. A system for processing a low-illuminance image, the system comprising:

an image acquisition unit to acquire two images having different levels of illuminance and sensitivity as first and second images;

a motion vector estimation unit to estimate a motion vector of the second image based on the first image;

an image correction unit to correct the second image using the estimated motion vector;

a synthesis coefficient calculation unit to calculate a synthesis coefficient used to synthesize the first image and the corrected second image; and

an image synthesis unit to synthesize the first image and the corrected second image using the calculated synthesis coefficient.

2. The system of claim 1, wherein the second image acquired by the image acquisition unit has lower illuminance and high sensitivity than the first image.

3. The system of claim 2, further comprising a noise reduction unit to reduce noise from the second image.

4. The system of claim 3, wherein the noise reduction unit comprises:

a noise level calculation unit to calculate a noise level of the second image;

a binary image generation unit to calculate a signal-to-noise ratio (SNR) of each pixel of the second image and to generate a binary image of the second image based on a threshold value;

a boundary reduction unit to smooth the boundary between an activated region and a deactivated region in the binary image; and

a filtering application unit to filter the binary image by applying a noise filter to the binary image.

5. The system of claim 1, wherein the motion vector estimation unit estimates the motion vector by creating an image pyramid for each of the first and second images by subsampling, in which length and width of each of the first and second images are reduced to a half of its original length and width, and calculating an optimal motion between the first and second images at each level of the image pyramids from highest to lowest.

6. The system of claim 1, wherein the motion vector estimation unit generates one-dimensional (1D) projection data of each of the first and second images and estimates a distance, which is traveled by the generated projection data and maximizes a similarity measure, as the motion vector by moving the generated projection data.

7. The system of claim 1, wherein the synthesis coefficient calculation unit comprises:

an edge extraction unit to convert the first image and the corrected second image into a first binary image and a second binary image, respectively;

an image combination unit to combine the first binary image and the second binary image using an OR operation and generating a combined binary image; and

an image smoothing unit to continuously convert a binary region by having a slope at the border of an activated region of the combined binary image.

8. The system of claim 7, wherein the activated region comprises pixels having a binary value of one after the OR operation.

9. The system of claim 7, wherein the synthesis coefficient calculation unit further comprises an image dilation unit expanding the border of the activated region of the combined binary image to a deactivated region.

10. The system of claim 1, wherein the image acquisition unit comprises:

a lens;

an image capturing sensor to capture an image received through the lens; and

an exposure/gain controller to control the exposure and sensitivity of the captured image.

11. A method of processing a low-illuminance image, the method comprising:

acquiring two images having different levels of illuminance and sensitivity as first and second images;

extracting a motion vector of the second image based on the first image;

correcting the second image using the extracted motion vector;

calculating a synthesis coefficient used to synthesize the first image and the corrected second image; and

synthesizing the first image and the corrected second image using the calculated synthesis coefficient,

wherein the method is performed with at least one processor.

12. The method of claim 11, wherein the acquired second image has lower illuminance and high sensitivity than the first image.

13. The method of claim 12, further comprising reducing noise from the second image after acquiring the first and second images.

14. The method of claim 13, wherein the reducing of the noise comprises:

calculating a noise level of the second image;

calculating an SNR of each pixel of the second image and generating a binary image of the second image based on a threshold value;

smoothing the boundary between an activated region and a deactivated region in the binary image; and

filtering the binary image by applying a noise filter to the binary image.

15. The method of claim 11, wherein the extracting of the motion vector comprises estimating the motion vector by creating an image pyramid for each of the first and second images by subsampling, in which length and width of each of the first and second images are reduced to a half of its original length and width, and calculating an optimal motion between the first and second images at each level of the image pyramids from highest to lowest.

16. The method of claim 11, wherein the extracting of the motion vector comprises:

generating 1D projection data of each of the first and second images; and

estimating a distance, which is traveled by the generated projection data and maximizes a similarity measure, as the motion vector by moving the generated projection data.

17. The method of claim 11, wherein the calculating of the synthesis coefficient comprises:

converting the first image and the corrected second image into a first binary image and a second binary image, respectively;

combining the first binary image and the second binary image using an OR operation and generating a combined binary image; and

continuously converting a binary region by having a slope at the border of an activated region of the combined binary image.

18. The method of claim 17, wherein the activated region comprises pixels having a binary value of one after the OR operation.

19. The method of claim 17, wherein the calculating of the synthesis coefficient further comprises expanding the border of the activated region of the combined binary image to a deactivated region.

20. A method of processing a low-illuminance image, the method comprising:

acquiring two images having different levels of illuminance and sensitivity as first and second images;

converting the first and second images into a first binary image and a second binary image, respectively;

generating a combined binary image by combining the first and second binary images using an OR operation;

continuously converting a binary number by having a slope at the border of an activated region of the combined binary image; and

synthesizing the first and second images using the continuously converted binary number of the combined binary image.

21. The method of claim 20, wherein the activated region comprises pixels having a binary value of one after the OR operation, and the calculating of the synthesis coefficient further comprises expanding the border of the activated region of the combined binary image to a deactivated region.

22. The method of claim 20, further comprising converting the first and second images into single-channel images, respectively, after acquiring the first and second images.

23. The method of claim 20, wherein in the converting of the first and second images into the first and second binary images, an SNR value of each pixel of each of the first and second images is calculated, and the first and second images are converted into the first and second binary images by setting each pixel to one if an SNR value of the pixel is greater than a predetermined threshold value and setting the pixel to zero if the SNR value of the pixel is less than the predetermined threshold value.