Methods and apparatus for calibrating a color display

• US 20060221093A1
• Filed: 05/30/2006
• Published: 10/05/2006
• Est. Priority Date: 04/11/2000
• Status: Active Grant

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: RAH Color Technologies LLC
• Inventors: Holub, Richard A.
• Granted Patent: US 7,710,433 B2
• Time in Patent Office: Days
• 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 for calibrating a color display coupled to a computer system comprising the steps of:

displaying one or more screens on said display; and

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.

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 to the computer system.

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, wherein said display is capable of being calibrated when said superposition of colors is observed.

9. The method according to claim 1 wherein said at least one display control 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 of at least said one color channel using said display control until superposition of colors is observed, wherein said display is capable of being calibrated when said superposition of colors is observed.

10. The method according to claim 1 further comprising the step of setting the neutral balance and tone reproduction of the display after said adjusting step is carried out.

11. 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.

12. 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.

13. 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.

14. 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. A system for calibrating a sensor having one or more channels which is useful for calibrating display surfaces comprising:

a reflective surface;

a measurement sensor and a reference sensor each directed toward one or more display surfaces;

a computer system coupled to the display, measurement sensor and reference sensor; and

a monochromator for illuminating the reflective surface with light of certain color in which the color of said light is controllable by the computer system and said measurement and reference sensors are capable of measuring the color of said reflective surface when illuminated by said monochromator to calibrate the measurement sensor in accordance with the measurements taken by both the measurement sensor and the reference sensor.

15. The system according to claim 4 wherein said one or more channels of said measurement sensor have spectral sensitivities that are not linearly related to color matching functions, and wherein said measurements enable the calculation of ratios capable of being used to calculate a tristimulus value corresponding to the response of said measurement sensor to a known light.

5. A method of calibrating color devices associated in a network comprising the steps of:

adjusting one or more devices to match one or more reference images;

measuring adjusted calibration parameters of said devices; and

storing said calibration parameters for use in calibrating said devices.

6. The method according to claim 5 wherein at least one of said devices represents a display and wherein said measuring step further comprises the step of measuring ambient illumination diffusely reflected from said display to provide measurements, wherein is measured and said measurements are incorporated with gamut color data.

7. The method according to claim 5 wherein said storing step further comprises the step of storing said parameters for use in calibrating said devices in a network for use in reproducing substantially the same colors within the capabilities of said devices.

8. The method according to claim 5 wherein at least one of said reference images represents a hard-copy image viewed under controlled illumination, said method further comprising the step of displaying digitally 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 digital 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, and said measuring step further comprising the step of measuring by said computer system at least one or more of tone reproduction or neutral balance of the visually matched digital image.

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

comparing a displayed screen color to a 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.

17. The method according to claim 16 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.

18. The method according to claim 17 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, 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.

19. A method for calibrating a color display comprising the steps of:

providing a user interface screen on the display with a plurality of patches ranging from low to high gray scale values;

comparing the displayed patches with a reference associated with said patches;

displaying on said user interface screen indicator levels of the gray scale value of each of said displayed patches and changing the indicator levels of one or more of said patches to match the associated patches of the reference; and

updating the calibration of the display in accordance with the values of the displayed gray scale patches when said displayed patches match the associated patches of the reference.

20. A system of colorimetry of a sensor comprising:

a sensor having at least one channel of spectral sensitivity which does not match the spectral sensitivity of color viewed by a human;

a color reference defining a mixture of a plurality of colorants each providing a spectral distribution;

said sensor measuring the color of said reference; and

a computer for producing a spectrum of a mixture of said colorants, convolving the spectral sensitivity of said sensor with the spectral distribution of said colorants to provide at least one integrated spectral value, and determining when said value corresponds to said measurement by said sensor to provide color coordinates of said mixture in a Standard Observer coordinate system.