Methods and apparatus for calibrating a color display

• US 7,710,433 B2
• Filed: 05/30/2006
• Issued: 05/04/2010
• Est. Priority Date: 04/11/2000
• Status: Expired due to Fees

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: RAH Color Technologies LLC
• Inventors: Holub, Richard A.
• Primary Examiner(s): Nguyen; Hau H
• Application Number:
  US11/442,882
• Publication Number:
  US 20060221093A1
• Time in Patent Office: 1,435 Days
• Field of Search: 345/589, 345/590, 345/593, 345/594, 345/597, 382/167, 358/518, 358/520
• US Class Current: 345/589
• CPC Class Codes: G01J 3/506 measuring the colour produced by screens, monitors, displays or CRTs
• CPC Class Codes: G06F 3/14 Digital output to display device ; Cooperation and interconnection of the display device with other functional units
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 2370/045 using multiple communication channels, e.g. parallel and serial
• CPC Class Codes: G09G 5/006 Details of the interface to the display terminal specific for a display terminal using a CRT G09G1/167; using a flat panel G09G3/2096; circuits for interfacing with colour displays G09G5/04
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 5/026 Control of mixing and/or overlay of colours in general G09G5/022 and G09G5/024 take precedence

Abstract

Improved methods are provided for calibrating color on a color display coupled to a computer, which are useful for obtaining calibrated data in a virtual proof network for enabling different color devices to render consistent color. Methods involve user interactions with screens on the display to set color display parameters. An apparatus is also provided for calibrating a sensor which may be used for measuring color of a display in one or more of these methods.

Claims

1. A method of calibrating one or more color devices comprising the steps of:

adjusting color rendering of one or more devices to subjectively match one or more visible references, wherein said one or more visible references are not being rendered by said one or more devices being adjusted; and

measuring one or more calibration parameters of said one or more devices in which said measuring step is carried out after said adjusting step, and said one or more calibration parameters are in device independent units of color for use in calibrating said one or more devices.

2. The method according to claim 1 wherein at least one of said one or more devices represents a display, and said measuring step further comprises the step of measuring ambient illumination to provide data capable of being incorporated with gamut color data.

3. The method according to claim 2 wherein said measuring step is carried out one of with a sensor or subjectively by a user.

4. The method according to claim 1 wherein said one or more devices are two or more in number, and said method further comprises the step of storing said one or more parameters for use in calibrating said devices to improve color matching between said devices.

5. The method according to claim 1 wherein at least one of said visible references represents a hard-copy image, said method further comprises the step of displaying an image corresponding to said hard-copy image on a video monitor, wherein said adjusting step further comprises the step of editing by a user said image with color editing software on a computer system until the user realizes a visual match between one or more aspects of said hard-copy image and said image on said video monitor.

6. The method according to claim 5 wherein said measuring step further comprises the step of measuring by said computer system at least one or more of tone reproduction or neutral balance of the visually matched image.

7. The method according to claim 6 further comprising the step of communicating one or more of said measured tone reproduction and neutral balance, or correction functions for one or more of said measured tone reproduction and neutral balance, by said computer system to one or more sites for use with one or more color rendering devices at said sites to improve color matching between said one or more color rendering devices and said one or more devices being calibrated.

8. The method according to claim 5 further comprising the step of storing data representative of said color editing in a transformation table which maps original colors of the monitor to the colors after said editing step is carried out.

9. The:

method according to claim 5 further comprising the step of calibrating one or more of tone reproduction and neutral balance of the color channels of the video monitor prior to carrying out said displaying and editing steps.

10. The method according to claim 1 wherein said measuring step is carried out one of with a sensor or subjectively by a user.

11. The method according to claim 1 further comprising the step of storing data representing at least one adjustment made to said one or more devices at said adjusting step.

12. The method according to claim 11 wherein said data comprises a transformation table for at least one of said one or more devices.

13. The method according to claim 1 wherein said one or more calibration parameters comprise one or more of tone reproduction, neutral balance, while point, color mixture data, ambient illumination, viewing conditions, offsets, gains, absolute luminance, head room, color temperature or gamma:

14. The method according to claim 1 wherein at least one of said one or more visible references represents a hard-copy image.

15. A method for modeling the color of a color display having a plurality of color channels comprising the steps of:

comparing subjectively a displayed screen color to a visible color reference;

changing the screen color to match the color reference;

recording the color of screen which matches the color reference;

measuring the displayed screen color which matches the color reference with a sensor, and storing the sensor measurement with the recorded screen color;

repeating said comparing, changing, recording, and measuring steps with different color references; and

modeling the relationship between the measurements and associated recorded screen colors to provide normative data of the color of the screen.

16. The method according to claim 15 further comprising the steps of:

increasing the contrast of the display to about a maximum level for the display;

increasing the brightness of the display for at least one color channel to about a maximum level for the display; and

lowering the brightness of the display of at least said one color channel until superposition of colors is observed.

17. The method according to claim 16 further comprising the steps of:

displaying at least one of the recorded screen colors;

comparing the displayed recorded screen color with the associated color reference;

changing the display screen color when needed to match the color reference;

recording the color of screen which matches the color reference;

measuring the displayed screen color which matches the color reference with a sensor to provide an updated sensor measurement, and storing the updated sensor measurement with the recorded screen color; and

updating the model when the screen color was changed to match the color reference in accordance with the stored updated sensor measurement.

18. The method according to claim 15 wherein said measuring step occurs after said changing step is carried out for each of said different color references.

19. The method according to claim 15 further comprising the step of modifying at least one of brightness or contrast of the display toward a superposition of colors.

20. The method according to claim 15 wherein said color reference is presented on said color display in proximity to said displayed screen color and said changing step further comprises changing the displayed screen color to obtain a visual match in a condition of metamerism between the color reference and said displayed screen color.

21. A method of sharing color-matching preferences between devices associated in a network comprising the steps of:

providing one or more visible references;

adjusting color reproduction settings for at least one of said devices in order to improve the subjective match of said one or more visible references to a reproduction of each of said one or more visible references, wherein said one or more visible references are not being rendered by said one of said devices being adjusted, and said adjusting step adjusts information utilized for rendering a reproduction on said one of said devices without adjustment of any physical setting of said one of said devices; and

providing said adjusted settings in device independent units of color in which said adjusted settings are shareable in a network.

22. The method according to claim 21 wherein at least one of said devices represents a display, and said method further comprises the step of providing data representative of ambient illumination with respect to said display.

23. The method according to claim 21 further comprising the step of sharing said adjusted settings in a network for use in calibrating devices in said network to enable improved color matching between said devices.

24. The method according to claim 21 wherein at least one of said one or more visible references represents a hard-copy image, said method further comprising the step of displaying an image corresponding to said hard-copy image on a video monitor, wherein said adjusting step further comprises the step of editing by a user said image with color editing software on a computer system until the user realizes a visual match between one or more aspects of said hard-copy image and said image on said video monitor.

25. The method according to claim 24 wherein said measuring step further comprises the step of measuring by said computer system one or more of tone reproduction or neutral balance of the visually matched image.

26. The method according to claim 21 further comprising the step of verifying the state of calibration of one or more of said devices, said state comprising at least white balance and tone reproduction settings, wherein said adjusting step adjusts color reproduction settings for at least one of said devices after said verifying step is carried out.

27. An apparatus for calibrating one or more color devices utilizing a computer system and one or more visible references comprising:

a program executable by a computer system to enable a user to adjust color rendering of each of said one or more devices to subjectively match the one or more visible references, wherein said one or more visible references are not being rendered by said one or more devices being adjusted; and

a sensor which enables measurement of one or more calibration parameters of said one or more devices whose color rendering was adjusted by the user, in which said one or more calibration parameters are in device independent units of color and usable in calibrating said one or more devices.

28. The apparatus according to claim 27 wherein said one or more color devices are two or more in number, and said one or more calibration parameters enable calibration of said color devices for use improving color matching between said devices.

29. The apparatus according to claim 27 wherein at least one of said one or more visible references represents a hard-copy image, at least one of said one or more color devices is a video monitor, and said program enables display of an image corresponding to said hard-copy image on the video monitor, and said program further comprises color editing software to enable the user to adjust color rendering on the video monitor until the user realizes a visual match between one or more aspects of said hard-copy image and said image on said video monitor.

30. A method for calibrating color rendering devices associated with one or more computer systems comprising the steps of:

updating the calibration of at least one of said color rendering devices by one or more of modifying tone reproduction curves for one or more color channels, producing a color to color'"'"'transformation or performing calibration which includes characterization of color mixture properties;

providing one or more visible references;

adjusting color reproduction settings for said at least one of said color rendering devices in order to improve the subjective match of said one or more visible references to reproductions of said one or more visible references by said at least one of said color rendering devices, in which said one or more visible references are not being rendered by said one of said devices being adjusted, and said adjusting step adjusts information utilized for rendering a reproduction on said one of said devices without adjustment of any physical setting of said one of said devices; and

storing said adjusted settings in device independent units in which said adjusted settings are useable to improve color matching between said color rendering devices.

31. The method according to claim 30 wherein said color to color'"'"'transformation comprises a gray balance correction.

32. The method according to claim 30 wherein said color rendering devices are different from each other in their rendering of color.

33. A computer-readable storage medium encoded with a computer program for calibrating one or more color devices comprising:

a program executable by a computer system to enable a user to adjust color rendering of each of said one or more devices to subjectively match one or more visible references, wherein said one or more visible references are not being rendered by said one or more devices being adjusted; and

said program receives data from a sensor representative of one or more calibration parameters of said one or more devices whose color rendering was adjusted by the user, in which said one or more calibration parameters are in device independent units of color and usable in calibrating said one or more devices.

34. The computer-readable storage medium according to claim 33 wherein said one or more color devices are two or more in number, and said one or more calibration parameters enable calibration of said color devices for use in improving color matching between said devices.

35. The computer-readable storage medium according to claim 33 wherein at least one of said one or more visible references represents a hard-copy image, at least one of said one or more color devices is a video monitor, and said program enables display of an image corresponding to said hard-copy image on the video monitor, and said program further comprises color editing software to enable the user to adjust color rendering on the video monitor until the user realizes a visual match between one or more aspects of said hard-copy image and said image on said video monitor.