Determining the color match between image data and graphics objects

• US 20070109569A1
• Filed: 11/17/2005
• Published: 05/17/2007
• Est. Priority Date: 11/17/2005
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Eschbach, Reiner, Fan, Zhigang, Rumph, David
• Granted Patent: US 7,649,649 B2
• Time in Patent Office: Days
• US Class Current: 358/1.900
• CPC Class Codes: G06T 7/90 Determination of colour characteristics

Abstract

A system/method of color match assessment for electronic documents includes receiving digital data defining a composite electronic document including a raster image object having an edge and a color graphics object bordering the edge of the raster image object. The pixel color values defining the edge of the raster image object are processed to estimate a local color variance of the pixel color values. The local color variance is used to determine if the edge can be color matched to the bordering color graphics object. If the edge can be color matched, a match color for the edge is derived. The match color is associated with the digital data defining the electronic document so that a downstream object color match system can use the match color as needed, e.g., to adjust the color of the bordering color graphics object to ensure a match with the edge of the raster image object when the electronic document is printed using a xerographic printing process.

Claims

1. A method of color match assessment for electronic documents, said method comprising:

(a) receiving digital data defining a composite electronic document including a raster image object having an edge and a color graphics object bordering said edge of said raster image object;

(b) processing pixel color values defining said edge of said raster image object to estimate a local color variance of said pixel color values defining said edge;

(c) using said local color variance to determine if said edge can be color matched;

(d) if said edge can be color matched, deriving a match color for said edge.

2. The method of color match assessment for electronic documents as set forth in claim 1, further comprising:

(d) associating said match color with said electronic document for use of said match color by a downstream object color match system.

3. The method of color match assessment for electronic documents as set forth in claim 2, wherein:

said raster image object comprises multiple edges and wherein said electronic document comprises multiple color graphics objects respectively bordering said multiple edges; and

,

for each one of said multiple edges, in order to derive a match color to be associated with each one of said multiple edges, respectively, said method comprises;

(b) processing pixel color values defining each edge of said raster image object to estimate a respective local color variance of said pixel color values defining each edge;

(c) using said local color variance of each edge to determine if the edge can be color matched;

(d) if an edge can be color matched, deriving a match color for the edge.

4. The method of color match assessment for electronic documents as set forth in claim 3, further comprising:

sending said digital data defining said composite electronic document and said match colors associated respectively with said multiple edges of said raster image object to an object color matching system of a xerographic image printing system.

5. The method of color match assessment for electronic documents as set forth in claim 1, wherein said match color is derived as an average of all pixel color values defining said edge.

6. The method of color match assessment for electronic documents as set forth in claim 1, wherein said match color is derived as a weighted average of all pixel color values defining said edge.

7. The method of color match assessment for electronic documents as set forth in claim 6, wherein pixels color values defining said edge and located farther from a center of said raster image object are weighted more in said weighted average as compared to pixel color values defining said edge and located closer to said center of said raster image object.

8. The method of color match assessment for electronic documents as set forth in claim 1, said local color variance of said pixel color values defining said edge is determined as:

V(y)=Σ

|I(x,y)−

I(y)÷

N

where;

V(y) represents the color variance of the row/column of pixel values;

N represents the number of pixel values in the row/column being processed;

Σ

|I(x,y)−

I(y)| represents the sum of the absolutes, meaning the sum of the absolute values of the difference between I(x,y)−

I(y) where I(x,y) is the pixel color value for a pixel being processed and I(y) is the mean of all color pixel values in the row/column being processed.

9. The method of color match assessment for electronic documents as set forth in claim 1, wherein the edge is defined by multiple rows/columns of said pixel color values, and wherein said step (b) of processing pixel color values defining said edge of said raster image object to estimate a local color variance of said pixel color values defining said edge comprises:

calculating a row/column local color variance for each row/column of said pixel color values defining said edge;

comparing said row/column local color variance for each row/column to a threshold;

including said row/column in a low variance region for said edge if said row/column local color variance is below said threshold.

10. The method of color match assessment for electronic documents as set forth in claim 9, wherein said step (c) using said local color variance to determine if said edge can be color matched comprises increasing a color matching score that said edge can be color matched based upon an increasing number of rows/columns included in said low variance region for said edge, wherein said color matching score monotonically increases with the number of rows/columns included in said low variance region for said edge.

11. The method of color match assessment for electronic documents as set forth in claim 9, wherein said threshold is set to an actual variance calculated for a row/column when said actual variance is below said threshold.

12. The method of color match assessment for electronic documents as set forth in claim 9, wherein said threshold varies depending upon a location of each row/column of pixel color values defining said edge, wherein said threshold is lower for rows/columns farther from a center of said raster image object.

13. In a xerographic printing apparatus, a method for color match assessment for electronic documents comprises:

receiving digital data defining a composite electronic document including a raster image object having an edge and a color graphics object bordering the edge of the raster image object;

determining if said edge and said color graphic object can potentially match in color;

if said edge and said color graphic object can potentially match in color, determining a match color for the edge;

saving said edge match color for use by a downstream object color match system to prevent said edge and said color graphics object from being printed in non-matching colors.

14. The method as set forth in claim 13, wherein said edge is defined by a plurality of different pixel color values, and wherein said match color for the edge is determined as an average of the pixel color values.

15. The method as set forth in claim 13, wherein said average is a weighted average and wherein pixel color values located farther from a center of said raster image object are weighted more than pixel color values located closer to the center of said raster image object.

16. The method as set forth in claim 13, wherein said step of determining if said edge and said color graphic object can potentially match in color comprises determining a color variance of pixel color values defining said edge.

17. The method as set forth in claim 16, wherein said step of determining a color variance comprises calculating a variance for multiple rows/columns of pixel color values defining said edge.

18. The method as set forth in claim 17, wherein rows/columns having a color variance below a threshold are included in a low variance region, and wherein said step of determining if said edge and said color graphic object can potentially match in color comprises determining the number of rows/columns included in the low variance region.

19. The method as set forth in claim 18, wherein a color matching score that the edge and the color graphics object can potentially match in color increases when a number of rows/columns in said low variance region increases.

20. An apparatus for color match assessment for electronic documents, said apparatus comprising:

means for input of digital data defining a composite electronic document including a raster image object having an edge and a color graphics object bordering said edge of said raster image object;

means for processing pixel color values defining said edge of said raster image object to estimate a local color variance of said pixel color values defining said edge;

means for using said local color variance to determine if said edge can be color matched;

means for deriving a match color for said edge.