Digital image processing system and method for processing digital images

• US 7,382,928 B2
• Filed: 08/06/2004
• Issued: 06/03/2008
• Est. Priority Date: 12/09/2003
• Status: Expired due to Fees

• Current Assignee: Chinese University of Hong Kong
• Original Assignee: Chinese University of Hong Kong
• Inventors: Tang, Xiaoou, Chu, Hoi Chung, Ho, Ying Fai, Leung, Kwok Yiu, Wong, Kam Fai
• Primary Examiner(s): Wu; Jingge
• Assistant Examiner(s): Patel; Jayesh A
• Application Number:
  US10/913,895
• Publication Number:
  US 20050123211A1
• Time in Patent Office: 1,397 Days
• Field of Search: 382/167, 382/172, 382/274, 382/279, 382/261
• US Class Current: 382/254
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 25/683 by defect estimation performed on the scene signal, e.g. real time or on the fly detection
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86
• CPC Class Codes: H04N 9/69 for modifying the colour signals by gamma correction controlling camera response for colour signals H04N23/83
• CPC Class Codes: H04N 9/73 Colour balance circuits, e.g. white balance circuits or colour temperature control camera processing pipelines for colour balance H04N23/88

Abstract

Disclosed is an automatic digital image enhancement method, including: determining the defects existing in the image based on pixel values, such as pixel luminance values and pixel color values, of the input digital image, and making corrections based on the determination results. The method can process images of digital photos, digital videos and make enhancement on exposure and color of the images. The method disclosed can also improve quickly and apparently the visual quality and appearance of images.

Claims

1. A method of processing a digital image comprising:

detecting pixel color values of pixels in said digital image;

determining whether or not a defect exists in said digital image by comparing detected pixel color values with a predetermined value; and

correcting said defect by adjusting said detected pixel color values if said defect exists, so as to output said digital image via a digital image processing device after said defect has been corrected;

wherein said correcting comprises;

determining a first color casting factor of pixels in a highlight region based on a predetermined largest color value and a predetermined smallest pixel color value among maximum values of red, green and blue histograms of the pixels of said digital image; and

transforming pixel color values of pixels in a highlight region to a larger pixel color value in accordance with said first color casting factor based on the following quotations, respectively;

R′

=Rmax+(BrightMax−

Rmax)×

CCBright

G′

=Gmax+(BrightMax−

Gmax)×

CCBright

B′

=Bmax+(BrightMax−

Bmax)×

CCBright

wherein;

Rmax, Gmax and Bmax are largest color values in red, green and blue color channels of histograms of said digital image, respectively;

BrightMax is the maximum among Rmax, Gmax and Bmax;

CCBright is said first color casting factor in said highlight region of said digital image; and

R′

, G′

, and B′

are respectively a color values of Rmax, Gmax and Bmax colors after processed.

2. The method according to claim 1, further comprising:

determining a second color casting factor of pixels in a shadow region based on a predetermined smallest color value and a predetermined largest color value among minimum values of red, green and blue histograms of the pixels of said digital image; and

transforming pixel color values of pixels in a shadow region to a smaller color value in accordance with said second color casting factor based on following quotations, respectively;

R′

=Rmin−

(Rmin−

DarkMin)×

CCDark

G′

=Gmin−

(Gmin−

DarkMin)×

CCDark

B′

=Bmin−

(Bmin−

DarkMin)×

CCDark

wherein;

Rmin, Gmin and Bmin are smallest color values in red, green and blue color channels of histograms of said digital image, respectively;

DarkMin is the minimum among Rmin, Gmin and Bmin;

CCDark is said second color casting factor in said shadow region of said digital image; and

R′

, G′

, and B′

are respectively a color values of Rmin, Gmin and Bmin colors after processed.

3. The method according to claim 2, further comprising:

transforming, so as to enhance visual image details, the color values of each pixel of said digital image based on a weighted mean value of luminance values of pixels within a predetermined distance adjacent to said each pixel, using a corresponding nonlinear monotonic increasing transformation function.

4. The method according to claim 3, wherein said weighted mean value is determined by a low pass filter.

5. The method according to claim 4, wherein the determining of said weighted value comprises:

scaling down said digital image from an original dimension to a predetermined dimension;

smoothing said digital image with said low pass filter;

scaling up said digital image to said original dimension to determine a luminance value of each current pixel of said digital image; and

determining said weighted mean value based on the luminance value of each current pixel of said digital image.

6. The method according to claim 5, further comprising dividing said image of the original dimension into corresponding rectangle blocks, and determining the pixel color value of each pixel of said digital image scaled down by taking a mean value of the pixel luminance values of the pixels in said corresponding rectangle block.

7. The method according to claim 1, wherein said digital image processing device is a digital camera or a digital video camera.