Color characterization of projectors

• US 20060071937A1
• Filed: 10/01/2004
• Published: 04/06/2006
• Est. Priority Date: 10/01/2004
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.), Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Tin, Siu-Kei
• Granted Patent: US 7,148,902 B2
• Time in Patent Office: Days
• US Class Current: 345/591
• CPC Class Codes: G01J 3/46 Measurement of colour; Colour measuring devices, e.g. colorimeters measuring colour temperature G01J5/60
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/506 measuring the colour produced by screens, monitors, displays or CRTs
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/001 using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background slide projectors per se G03B23/00 = 42 HP
• 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

Abstract

The present invention transforms a device-dependent color value in a device-dependent color space of a display device to a device-independent color value in a device-independent color space. A first color value is determined in a perceptually linear color space by applying a matrix model to the device-dependent color value, the matrix model applying a tone curve correction and a tristimulus matrix to the device-dependent color value. A difference value is then determined in the perceptually linear color space, wherein the difference value is determined by applying a difference model to the device-dependent color value, and wherein the difference model models deviation of the matrix model from actual measurements of the display device. Next, the difference value and the first color value are added and the sum is transformed to the device-independent color space. Because the first value based on the matrix model is added to a difference value which accounts for deviation of the matrix model, the present invention can account for the channel interdependency prevalent in DLP display devices.

Claims

1. A method for transforming a device-dependent color value in a device-dependent color space of a display device to a device-independent color value in a device-independent color space, the method comprising the steps of:

a first determining step of determining a first color value in a perceptually linear color space by applying a matrix model to the device-dependent color value, the matrix model applying a tone curve correction and a tristimulus matrix to the device-dependent color value;

a second determining step of determining a difference value in the perceptually linear color space, wherein the difference value is determined by applying a difference model to the device-dependent color value, and wherein the difference model models deviation of the matrix model from actual measurements of the display device; and

adding the difference value and the first color value and transforming the sum to the device-independent color space.

2. A method according to claim 1, wherein the difference model comprises a look-up table (LUT), and wherein the difference value is determined based on linear interpolation of values in the LUT.

3. A method according to claim 2, wherein the values in the LUT are non-uniformly spaced corresponding to non-uniformly spaced actual measurements of the display device.

4. A method according to claim 1, wherein application of the matrix model provides a color value in the device-independent color space, and wherein said first determining step comprises transformation of the color value in the device-independent color space to the first color value in the perceptually linear color space.

5. A method according to claim 1, wherein the display device exhibits channel interdependency such that color channels of the device-dependent color value function interdependently during transformation from the device-dependent color value to the device-independent color value.

6. A method according to claim 5, wherein the channel interdependency is based on the effect of a white filter on a color wheel in the display device.

7. A method according to claim 5, wherein the channel interdependency is based on a non-linear 3D LUT implemented in the hardware of the display device.

8. A method according to claim 1, wherein the display device is a projector.

9. A method according to claim 1, wherein the device-independent color space is CIEXYZ.

10. A method according to claim 1, wherein the perceptually linear color space is CIELUV.

11. An apparatus for converting device-independent color values to device-dependent color values, wherein the apparatus utilizes the matrix model and the difference model of claim 1 to convert device-independent color values into device-dependent color values usable by the display device.

12. Computer-executable process steps stored on a computer readable medium, said computer-executable process steps for transforming a device-dependent color value in a device-dependent color space of a display device to a device-independent color value in a device-independent color space, said computer-executable process steps comprising process steps executable to perform a method according to any of claims 1 to 10.

13. A computer-readable medium which stores computer-executable process steps, the computer-executable process steps for transforming a device-dependent color value in a device-dependent color space of a display device to a device-independent color value in a device-independent color space, said computer-executable process steps comprising process steps executable to perform a method according to any of claims 1 to 10.