Characterizing color input devices with well-behaved extrapolation
View Patent ↗The present invention generates a color characterization model for performing transformation from a device-dependent color space of a color device to a device-independent color space. A first set of color measurement data is accessed corresponding to actual measurements of the color device, wherein the actual measurements define a measurement range in the device-dependent color space, and wherein the measurement data includes data point pairs, each data point pair having corresponding device-dependent values and device-independent values. Next, a second set of data point pairs is generated based on a predesignated set of device-dependent values outside the measurement range, by extrapolating device-independent values from the first set of color measurement data. The color characterization model is then determined based on both the first set of color measurement data and the generated second set of data point pairs. Because the color characterization model is determined based on actual measurements and extrapolated values, the color characterization model is well-behaved and does not exhibit significant overshooting or undershooting beyond the measurement range.
1. A method for generating a color characterization model for a color input device, the color characterization model for performing transformation from a device-dependent color space of the color input device to a device-independent color space, the method comprising the steps of:
accessing a first set of color measurement data corresponding to actual measurements of a color target by the color input device, wherein the color target has known color values in the device-independent color space and the actual measurements are obtained by the color input device in the device-dependent color space, wherein the actual measurements define a measurement range in the device-dependent color space, and wherein the measurement data includes data point pairs, each data point pair having corresponding actual measurements and known color values;
generating a second set of data point pairs based on plural device-dependent values outside the measurement range, by extrapolating device-independent values corresponding to the device-dependent values outside the measurement range from the first set of color measurement data; and
determining the color characterization model based on both the first set of color measurement data and the generated second set of data point pairs.
2. The method according to claim 1 , wherein said generating step comprises extrapolation of device-independent values from the first set of color measurement data based on distance and hue angle.
3. The method according to claim 1 , wherein the first set of color measurement data is obtained from a measurement-only color profile corresponding to the color input device.
4. The method according to claim 1 , wherein the color characterization model is usable by a color management system.
5. The method according to claim 1 , wherein said determining step comprises multivariate linear regression.
6. The method according to claim 1 , wherein said determining step comprises nonlinear regression.
7. The method according to claim 1 , wherein the plural device-independent values outside the measurement range includes device dependent values at at least one corner point of the device-dependent color space.
8. The method according to claim 1 , wherein the plural device-dependent values outside the measurement range correspond to eight corner points of the device-dependent color space.
9. The method according to claim 1 , wherein the plural device-dependent values outside the measurement range correspond to at least one axis boundary of the device-dependent color space.
10. The method according to claim 1 , wherein said generating step comprises extrapolation using Shepard extrapolation.
11. The method according to claim 1 , wherein the device-dependent color space is RGB.
12. The method according to claim 1 , wherein the device-independent color space is CIELUV.
13. The method according to claim 1 , wherein the device-independent color space is CIELAB.
14. The method according to claim 1 , wherein the device-independent color space is JAB.
15. The method according to claim 1 , wherein the color input device is a color scanner.
16. The method according to claim 1 , wherein the color input device is a digital color camera.
17. A computer-readable storage medium which stores computer-executable process steps, the computer-executable process steps executable by a computer to generate a color characterization model for a color input device, the color characterization model for performing transformation from a device-dependent color space of the color input device to 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 16 .
18. An apparatus for generating a color characterization model for a color input device, the color characterization model for performing transformation from a device-dependent color space of the color input device to a device-independent color space, the apparatus comprising:
obtaining unit configured to obtaining a first set of color measurement data corresponding to actual measurements of a color target by the color input device, wherein the color target has known color values in the device-independent color space and the actual measurements are obtained by the color input device in the device-dependent color space, wherein the actual measurements define a measurement range in the device-dependent color space, and wherein the measurement data includes data point pairs, each data point pair having corresponding actual measurements and known color values;
generating unit configured to generate a second set of data point pairs based on plural device-dependent values outside the measurement range, by extrapolating device-independent values corresponding to the device-dependent values outside the measurement range from the first set of color measurement data; and
determining unit configured to determine the color characterization model based on both the first set of color measurement data and the generated second set of data point pairs.