Methods and apparatus for calibrating a color display

• US 20100182335A1
• Filed: 03/22/2010
• Published: 07/22/2010
• Est. Priority Date: 04/11/2000
• Status: Active Grant

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: Richard A. Holub
• Inventors: Holub, Richard A.
• Granted Patent: US 8,009,175 B2
• Time in Patent Office: Days
• US Class Current: 345/590
• 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 for calibrating a color display coupled to a computer system comprising the steps of:

displaying one or more screens on said display;

adjusting at least one display control of the display when said one or more screens are displayed to provide superposition of color of the display;

setting the neutral balance and tone reproduction of the display in accordance with values stored on said computer system after said adjusting step is carried out;

enabling a measurement of ambient illumination with respect to said display; and

producing a color transformation which enables accurate rendering of colors expressible in device independent units upon the display, said color transformation comprising a chromatic adaptation transform useable to adjust for change in viewing conditions.

2. The method according to claim 1 further comprising the step of providing at least one sensor directed toward said display for measuring the color of the display.

3. The method according to claim 1 wherein said at least one display control represents two display controls for contrast and brightness, respectively, and said adjusting step further comprises the steps of:

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

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

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

7. The method according to claim 1 wherein said at least one display control is for brightness of the display, and when said contrast of the display is at a set level for said display said adjusting step further comprises the steps of:

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

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

8. The method according to claim 3 wherein said lowering step further comprises the step of lowering the brightness in visually detected increments using said display control for brightness.

9. The method according to claim 3 wherein said lowering step further comprises the steps of:

incrementally lowering the brightness of the display using said display control for brightness;

measuring the color of the display with a sensor directed to the display to determine when superposition occurs; and

repeating said incrementally lowering step and measuring color step until superposition is observed.

10. The method according to claim 3 wherein said lowering step further comprises the steps of:

incrementally lowering the brightness of the display using said display control for brightness;

observing by a user when the superposition of colors occurs by detection of threshold changes against a background; and

repeating said incrementally lowering step and observing step until superposition is observed.

11. The method according to claim 3 further comprising the step of:

measuring with a sensor the screen at increments of visually detected thresholds of color changes in one or more color channels.

4. -6. (canceled)

12. A method of colorimetry comprising the steps of:

providing spectral distributions of a plurality of colorants of a reproduction system;

measuring, with a sensor having one or more channels, one or more colors produced by mixing said colorants in various proportions;

computing spectral distributions corresponding to mixtures of said colorants;

convolving the spectral response of said sensor with the results of said computing step to provide one or more values; and

determining when said one or more values corresponds to the results of said measuring of said one or more colors by said sensor in order to provide color coordinates of said one or more colors in a coordinate system based upon human color perception.

13. The method according to claim 12 wherein the spectral response of said sensor in said one or more channels is compared to one or more color matching functions to provide ratios.

14. The method according to claim 13 wherein said ratios are useable in calculating said color coordinates in accord with human vision.

15. The method according to claim 13 further comprising the step of measuring responses of said sensor to known monochromatic light.

16. The method according to claim 13 wherein said sensor is an area sensor useable in measuring display surfaces and said sensor is further calibrated to compensate for one of optical distortion or differential sensitivity across the sensor array.

17. A computer-readable medium encoded with a computer program operable at a client computer with a display and having access to a computer server over a network comprising:

one or more screens enabling collection of data characterizing one or more viewing conditions of the display to determine effect of said viewing conditions on gamut of the display; and

at least one module for comparing said gamut of the display with another gamut for reproduction of an image received by the client computer from the computer server.

18. The computer-readable medium according to claim 17 further comprising, responsive to said comparing of said gamut with said another gamut, enabling one or more of rendering said image, enlarging the reproduction gamut of the display at the client computer, scaling the gamut of said image, or providing indication that colors are reproduced inaccurately.

19. The computer-readable medium according to claim 17 further enabling measurement of ambient illumination with respect to said display.

20. The computer-readable medium according to claim 19 wherein calibration of said display is modifiable responsive to said measurement of said ambient illumination.