Color-matched printing

• US 4,751,535 A
• Filed: 10/15/1986
• Issued: 06/14/1988
• Est. Priority Date: 10/15/1986
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Myers, Robin D.
• Primary Examiner(s): Evans, Arthur G.
• Application Number:
  US06/919,113
• Time in Patent Office: 608 Days
• Field of Search: 358/80, 358/75, 346/157, 355/4, 346/74.7, 346/204, 346/1.1, 364/518-521
• US Class Current: 347/115
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut
• CPC Class Codes: Y10S 347/90 Data processing for electrostatic recording

Abstract

A technique is disclosed for matching a color, applicable for example to printing a color which matches a color on a CRT display. Quantities of toners which will generate the matching color are determined and then a pattern of toners which will approximate those quantities is applied. To determine the quantities, a definition of the original color, such as its RGB coordinates, is converted to coordinates in a linear mixing space, such as CIE coordinates. These coordinates, together with coordinates of the toners are then used to calculate quantities of toners which will produce a matching color. The calculations match hue, saturation and reflectance so that the matching color appears like the original color and so that characteristics of an original image are preserved. A table containing the area coverages of available toner patterns is used in selecting the toner pattern. A separate pattern for each toner may be selected by comparing the quantity of that toner with the area coverages of its available patterns to find the separate toner pattern which will come closest to that quantity. The selected separate patterns of the toners are then combined to obtain a combined toner pattern, which is then applied.

Claims

1. A method comprising:

determining quantities of primary coloring agents to generate a hue approximating that of an original color; and

determining a quantity of at least one neutral coloring agent to adjust the hue so that the determined coloring agent quantities can be used to generate a color approximating the original color.

2. The method of claim 1, further comprising:

determining quantities of original coloring agents which generate the original color; and

determining linear mixing coordinates of the original color based on the quantities of original coloring agents which generate the original color;

the step of determining quantities of primary coloring agents comprising using the linear mixing coordinates of the original color and linear mixing coordinates of at least two of the primary coloring agents;

the step of determining the neutral coloring agent quantity comprising using the linear mixing coordinates of the original color and linear mixing coordinates of at least one neutral coloring agent.

3. The method of claim 2 in which the original coloring agents are additive RGB coloring agents, the step of determining quantities of original coloring agents comprising obtaining quantities of the additive RGB coloring agents, the step of determining the original color'"'"'s coordinates comprising converting the obtained quantities of additive RGB coloring agents into coordinates in CIE color space.

4. The method of claim 2 in which the step of determining quantities of primary coloring agents further comprises using two-dimensional linear mixing coordinates of the original color and of at least two of the primary coloring agents.

5. The method of claim 1 further comprising selecting a pattern which closely approximates the determined quantity of each coloring agent and applying the coloring agents in the pattern.

6. The method of claim 5 in which the substep of selecting the pattern comprises, for each coloring agent to be applied, selecting from a set of available separate patterns of that coloring agent a separate pattern which most closely approximates the determined quantity of that coloring agent;

the step of selecting the pattern further comprising combining the selected separate patterns for all of the coloring agents to be applied into a combined pattern of coloring agents which closely approximates the determined quantity of each coloring agent.

7. The method of claim 5, further comprising storing an area coverage value for each of a set of available coloring agent patterns, the step of selecting the pattern comprising comparing the determined quantity of each coloring agent with stored area coverage values of the available coloring agent patterns which include that coloring agent to find the available pattern whose stored area coverage value most closely approximates the determined quantity of that coloring agent.

8. The method of claim 7 in which the step of storing an area coverage value for each of the available patterns comprises measuring the reflectance of each of the available patterns and calculating an area coverage value for each pattern based on its measured reflectance.

9. The method of claim 8 in which the step of storing an area coverage value further comprises correcting the calculated area coverage value for at least one of the available patterns based on the calculated area coverage values for other available patterns.

10. A method comprising:

performing linear mixing calculations with an original color'"'"'s linear mixing coordinates and linear mixing coordinates of at least two primary coloring agents and at least one neutral coloring agent to determine quantities of the coloring agents to be used to generate a color approximating the original color.

11. The method of claim 10, further comprising determining the linear mixing coordinates of the original color and of the coloring agents prior to the step of performing linear mixing calculations.

12. The method of claim 10 in which the step of performing linear mixing calculations comprises performing two-dimensional linear mixing with linear mixing coordinates of the original color and the primary coloring agents to obtain linear mixing coordinates of a hue approximating that of the original color.

13. The method of claim 10 in which the step of determining coordinates comprises using quantities of original coloring agents which generate the original color to find the original color'"'"'s linear mixing coordinates.

14. The method of claim 13 in which the quantities of original coloring agents are quantities of additive RGB color agents, the linear mixing color space is the CIE color space, and the substep of using the quantities to find the coordinates comprises converting the RGB quantities into CIE coordinates.

15. The method of claim 10, further comprising selecting the at least two primary coloring agents from six primary coloring agents, the six primary coloring agents including three subtractive CMY coloring agents and three subtractive RGB coloring agents generated from the subtractive CMY coloring agents.

16. The method of claim 10, further comprising selecting the at least two primary coloring agents from at least three primary coloring agents.

17. The method of claim 16 in which the step of performing linear mixing calculations further comprises calculating relative quantities of the selected primary coloring agents which will generate a hue approximating that of the original color.

18. The method of claim 17 in which the step of performing linear mixing calculations further comprises calculating relative quantities of the hue and of at least one neutral coloring agent which will adjust the saturation and reflectance of the hue to generate a color approximating the original color.

19. The method of claim 18 in which the substep of calculating relative quantities of the hue and at least one neutral coloring agent comprises calculating relative quantities so that the color approximating the original color, when included in an image with other colors similarly generated to approximate colors in the original image containing the original color, will preserve color characteristics of the original image.

20. The method of claim 18 in which the step of performing linear mixing calculations further comprises calculating actual quantities of the primary coloring agents and the neutral coloring agent from the relative quantities.

21. The method of claim 16, in which the coordinates of the at least three primary coloring agents define a polygon, the method further comprising selecting linear mixing coordinates of a center point within the polygon, the step of selecting primary coloring agents comprising selecting two of the at least three primary coloring agents whose coordinates define vertices at ends of a side of the polygon which intersects a line projecting from the center point'"'"'s coordinates through the original color'"'"'s linear mixing coordinates.

22. The method of claim 21 in which the step of performing linear mixing calculations further comprises calculating relative quantities of the selected primary coloring agents based on lengths of parts of the side of the polygon.

23. The method of claim 22 in which the step of performing linear mixing calculations further comprises calculating relative quantities of a mixture of the selected primary coloring agents and of at least one neutral coloring agent based on lengths of parts of the projecting line.

24. The method of claim 21 in which the step of selecting coordinates of the center point comprises selecting the linear mixing coordinates of a neutral color along a neutral linear mixing line between coordinates of two neutral coloring agents, the natural color having a reflectance equal to that of the original color.

25. The method of claim 12 in which the substep of performing two-dimensional linear mixing comprises determining quantities of the primary coloring agents to be applied to generate the hue.

26. The method of claim 12 in which the step of performing linear mixing calculations further comprises performing two-dimensional linear mixing with linear mixing coordinates of the hue and the neutral coloring agent to determine a neutral coloring agent quantity to adjust the hue to obtain the color approximating the original color.

27. The method of claim 26 in which the substep of performing two-dimensional linear mixing with coordinates of the hue and the neutral coloring agent comprises adjusting the hue'"'"'s reflectance to be equal to the original color'"'"'s reflectance.

28. The method of claim 26 in which the substep of performing two-dimensional linear mixing with coordinates of the hue and the neutral coloring agent comprises adjusting the hue'"'"'s saturation to be equal to the original color'"'"'s saturation.