Background suppression method and apparatus

• US 20070019257A1
• Filed: 07/20/2005
• Published: 01/25/2007
• Est. Priority Date: 07/20/2005
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Li, Xing
• Granted Patent: US 7,551,334 B2
• Time in Patent Office: Days
• US Class Current: 358/518
• CPC Class Codes: H04N 1/4072 dependent on the contents of the original

Abstract

An original image is received in a red-green-blue color space. Pixels in the original image are converted to a luminance-chrominance color space. Background pixels in the original image are determined by comparing a luminance value of each pixel to a selectable luminance threshold, and comparing chrominance value of each pixel to a predetermined chrominance threshold. Chrominance values of the background pixels in each chrominance channel are adjusted.

Claims

1. A method comprising:

receiving an original image in a red-green-blue color space;

converting pixels in the original image to a luminance-chrominance color space;

determining background pixels in the original image including;

comparing a luminance value of each pixel to a selectable, adjustable luminance threshold value, and

comparing chrominance value of each pixel to a predetermined chrominance threshold value; and

adjusting chrominance values of the determined background pixels in each chrominance channel.

2. The method of claim 1, wherein each background pixel has the luminance value equal to or greater than the selectable luminance threshold value and the chrominance value less than the chrominance threshold value.

3. The method of claim 2, wherein the selectable luminance threshold value is equal to a difference between a luminance threshold value and a luminance threshold value offset.

4. The method of claim 1, further including:

prior to the step of adjusting the chrominance values, creating a chrominance adjustment table and wherein the step of adjusting the chrominance values includes;

adjusting the chrominance values of the background pixels in each chrominance channel based on a chrominance adjustment table.

5. The method of claim 4, further including:

prior to creating the chrominance adjustment table, determining a neutral chrominance value;

determining a range of chrominance grayscale values which lie in a neighborhood of the neutral chrominance value; and

limiting the chrominance adjustment only to the determined range of chrominance grayscale values.

6. The method of claim 5, wherein the step of adjusting the chrominance values further includes:

continuously smoothly adjusting the chrominance values of the background pixels to adjust the pixels closest to the neutral value the most and pixels furthest from the neutral value the least.

7. The method of claim 1, further including:

prior to the step of adjusting the chrominance values, creating a chrominance adjustment table for each chrominance channel and wherein the step of adjusting the chrominance values includes;

adjusting the chrominance values of the background pixels in each chrominance channel based on a corresponding chrominance adjustment table.

8. The method of claim 7, further including:

prior to creating the chrominance adjustment tables, determining a neutral chrominance value;

determining a range of chrominance grayscale values of each chrominance channel which chrominance grayscale values lie in a neighborhood of the neutral chrominance value; and

limiting the chrominance adjustment in each channel only to corresponding determined range of chrominance grayscale values.

9. The method of claim 1, further including:

determining a reference luminance background level; and

adjusting the luminance value of at least some background pixels to the reference luminance background level.

10. A document processing device for performing the steps of claim 1.

11. The method of claim 10, wherein the document processing device includes a xerographic marking engine.

12. A document processing system comprising:

a device for producing red-green-blue color pixel representation of an original image;

a red-green-blue color space to luminance-chrominance color space converter for converting values of red-green-blue pixels into corresponding luminance-chrominance pixel values;

a white pixel determining processor or algorithm for determining background pixels in the original image by comparing a luminance value of each pixel to a selectable, adjustable luminance threshold value, and comparing chrominance value of each pixel to a predetermined chrominance threshold value; and

a chrominance values adjusting processor or algorithm for adjusting chrominance values of each determined background pixel in each chrominance channel.

13. The system of claim 12, wherein each background pixel has the luminance value equal to or greater than the selectable luminance threshold value and the chrominance value less than the chrominance threshold value.

14. The system of claim 13, wherein the selectable luminance threshold value is equal to a difference between a reference luminance threshold value and a luminance threshold value offset.

15. The system of claim 12, further including:

a chrominance adjustment table for adjusting chrominance values of each background pixel in each chrominance channel in accordance with entries in the chrominance adjustment table.

16. The system of claim 15, wherein the chrominance adjustment table includes:

a predetermined range of entries, each entry corresponding to an output chrominance value which lies in a neighborhood of a neutral value to limit the chrominance adjustment only to the predetermined range of the chrominance output values.

17. The system of claim 12, further including:

first and second chrominance adjustment tables for adjusting chrominance values of each background pixel in each corresponding chrominance channel in accordance with entries in associated chrominance adjustment table.

18. The system of claim 12, further including:

a luminance adjustment processor or algorithm which adjusts the luminance values of the background pixels to a predetermined luminance value.

19. A method comprising:

receiving an original image in a red-green-blue color space;

converting pixels in the original image to a luminance-chrominance color space;

determining background pixels in the original image including;

comparing a luminance value of each pixel to a luminance threshold, and

comparing chrominance values of each pixel to a predetermined chrominance threshold; and

adjusting chrominance values of the determined background pixels in each chrominance channel in accordance with a prespecified chrominance adjustment table.

20. The method of claim 19, wherein the step of adjusting chrominance values includes:

adjusting chrominance values of the background pixels which have luminance values less than the luminance threshold.