Methods and apparatus for calibrating a color display

• US 9,500,527 B2
• Filed: 03/03/2014
• Issued: 11/22/2016
• Est. Priority Date: 04/11/2000
• Status: Expired due to Term

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: RAH Color Technologies LLC
• Inventors: Holub, Richard A.
• Primary Examiner(s): Martello, Edward
• Application Number:
  US14/195,334
• Publication Number:
  US 20140176948A1
• Time in Patent Office: 995 Days
• Field of Search: None
• US Class Current: 1/1
• 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 system of colorimetry of a sensor comprising:

a color reference defining a mixture of a plurality of colorants, said mixture providing a spectral distribution of light rendered in a substantially uniform field upon a display;

a sensor for measuring color of said reference in one or more channels, in which each of said one or more channels has a spectral response function; and

one or more programs executable by a computer system for convolving the spectral response function of each of said one or more channels of said sensor with said spectral distribution defined by said reference to provide one or more values, determining when said one or more values corresponds to the measurement of color of said reference by said sensor to provide one or more color coordinates of said reference in a Standard Observer coordinate system, calculating ratios, as a function of wavelength, of values of one or more color matching functions of the Standard Observer to values of the spectral response function of one or more channels of said sensor, and storing said ratios in memory of the computer system.

2. The system according to claim 1 wherein said ratios enable at least partial compensation for deviations of said spectral response function of each of said one or more channels of said sensor from said one or more color matching functions.

3. The system according to claim 1 further comprising memory which stores a relationship between the spectral response functions of said one or more channels of said sensor and one or more color matching functions of the Standard Observer.

4. The system according to claim 3 wherein at least said sensor, said source and said memory are linked to said computer system and said one or more programs compute said stored relationship.

5. The system according to claim 1 wherein said sensor is calibrated against a source providing wavebands of light spanning the visible spectrum.

6. The system according to claim 5 wherein the correspondence of said one or more values to said measurement by said sensor of said reference verifies the calibration of said sensor with respect to said source.

7. The system according to claim 5 wherein said sensor represents a first sensor, and said source is calibrated against a second sensor whose spectral response calibration is traceable to a standards laboratory.

8. The system according to claim 7 wherein said source is controlled by said computer system to provide said wavebands of light spanning the visible spectrum sequentially for detection by said second sensor, in which said source comprises at least a lamp and dispersive optics, wherein said second sensor records relative output of said source in each said waveband for functional association with responses of said first sensor.

9. An apparatus for calibrating a sensor for video display colorimetry comprising:

a source that is spectrally variable and controlled by a computer to spectrally vary said source to provide light in different wavebands across at least the visible spectrum;

a first sensor comprising a plurality of channels;

a second sensor calibrated to enable CIE colorimetry whose calibration is traceable to a standards laboratory, wherein said first sensor and said second sensor receive light from said source; and

said computer being operable to execute programs to at least;

control said source to provide said light in said different wavebands across at least the visible spectrum, receive data from said second sensor representing measured light from said source in said different wavebands, determine a relationship between said data and amounts of light provided by said source of said different wavebands so as to calibrate output of said source as a function of said wavebands, and calibrate said channels of said first sensor against said light from said calibrated source.

10. The apparatus according to claim 9 wherein said source represents a first source, and said apparatus further comprises a second source whose output comprises a plurality of spectral distributions, wherein said second source is utilized in verification of calibration of said first sensor.

11. The apparatus according to claim 10 wherein one of said programs executable by said computer calculates an expected amount of light to be measured by said first sensor of said second source, and compares the calculated expected amount of light with actual measured light of said second source by said first sensor to verify calibration of said first sensor.

12. The apparatus according to claim 10 wherein said calibration of said first sensor against said light from said calibrated source provides a spectral response function of each of said one or more channels of said first sensor, and said programs executable by said computer further convolve said spectral response function of each of said one or more channels of said first sensor with a spectral distribution provided by said second source to compute at least one value representing the expected amount of light to be measured by said first sensor, and compares said value with the actual measured light of said second source to verify calibration of said first sensor.

13. The apparatus according to claim 9 wherein said second sensor provides spectral data.

14. The apparatus according to claim 13 further comprising a surface that receives said light from said source, wherein said surface resides in a plane perpendicular to a line extending from said source through one or more lenses and wherein said first sensor and said second sensor receive said light from said source reflected from said surface along an angle between said plane and said line and on either side of said line, respectively.

15. The apparatus according to claim 13 wherein said first sensor and said second sensor record measurements at or about a same time.

16. A method for calibrating a sensor for video display colorimetry comprising the steps of:

providing a first sensor having one or more channels for detecting light and a second sensor calibrated to enable CIE colorimetry wherein the calibration of said second sensor is traceable to a standards laboratory;

controlling a source with the aid of a computer to provide light that spectrally varies in different wavebands across at least the visible spectrum;

measuring said light of said different wavebands from said source with the aid of said second sensor;

determining a relationship between measurements of said light of said different wavebands by said second sensor and amounts of light provided by said source of said different wavebands to calibrate said light from said source; and

calibrating spectral response functions of said channels of said first sensor against said light from said calibrated source.

17. The method according to claim 16 wherein said source represents a first source, and said method further comprises the step of providing light of a plurality of spectral distributions spanning a plurality of wavelengths from a second source, wherein said second source is utilized in verification of calibration of said first sensor.

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

calculating an expected measurement by said first sensor of said second source;

measuring by said first sensor said light from said second source to provide actual measurement of said second source; and

comparing the calculated expected measurement with actual measurement of said second source by said first sensor to verify calibration of said first sensor.

19. The method according to claim 16 wherein said second sensor provides spectral data.

20. The method according to claim 19 further comprising the steps of:

positioning a surface to occupy a plane perpendicular to a line extending from said source through one or more lenses to said surface; and

configuring said first sensor and said second sensor to receive said light from said source reflected from said surface along an angle between said plane and said line in which said first and second sensor each occupy positions on either side of said line.

21. The method according to claim 19 further comprising the step of operating said computer to record measurements by said first sensor and said second sensor at or about a same time.