Methods and system for improved color characterization
View Patent ↗Methods and systems are presented for characterizing a printer, display or other color reproduction device in which parametric and nonparametric forward color transforms are generated to construct a forward color device transform to characterize the mapping of CMYK input data to La*b* data of the device, with the parametric transform adapted to compensate for drifting performance of the color reproduction device.
1. A method of characterizing a color reproduction device, the method comprising:
producing a plurality of visible color images using the color reproduction device according to an input initial characterization data set in a first color space;
measuring the color images to generate a measured initial characterization data set in a second color space;
using at least one processor, generating a parametric forward color transform mapping color from the first color space to the second color space using the input initial characterization data set and the measured initial characterization data set;
using the at least one processor, generating an estimated initial characterization data set using the parametric forward color transform and the input initial characterization data set;
using the at least one processor, generating a nonparametric forward color transform mapping color from the first color space to the second color space using the measured and estimated initial characterization data sets; and
using the at least one processor, constructing a forward color transform for the device using the parametric and nonparametric forward color transforms.
2. The method of claim 1 , wherein producing the plurality of visible color images comprises printing a plurality of visible color patches using a printer, and wherein measuring the color images comprises scanning the printed color patches to generate the measured initial characterization data set.
3. The method of claim 1 , wherein producing the plurality of visible color images comprises rendering a plurality of visible color patches on a display.
4. The method of claim 1 , wherein the input initial characterization data set is a four-dimensional data set with C, M, Y, and K values in the first color space, and wherein the measured and estimated initial characterization data sets are three-dimensional data sets with L, a*, and b* values in the second color space.
5. The method of claim 1 , wherein generating the parametric forward color transform comprises fitting a polynomial surface to the initial characterization data.
6. The method of claim 1 , wherein generating the estimated initial characterization data set comprises evaluating values of the input initial characterization data set using the parametric forward color transform to generate the estimated initial characterization data set, and wherein generating the nonparametric forward color transform comprises subtracting the estimated initial characterization data set values from the measured initial characterization data set values to determine residual difference values.
7. The method of claim 1 , wherein the forward color transform for the device is constructed as a summation of the parametric and interpolated nonparametric forward color transforms.
8. The method of claim 1 , further comprising adapting the nonparametric forward color transform.
9. The method of claim 8 , wherein adapting the nonparametric forward color transform comprises:
producing a plurality of visible adaptation images using the color reproduction device according to an input adaptation data set in the first color space;
measuring the adaptation images to generate a measured adaptation data set in the second color space; and
adapting the parametric forward color transform using the input adaptation data set and the measured adaptation data set.
10. The method of claim 9 , wherein producing the plurality of visible adaptation images comprises printing a plurality of visible adaptation patches using a printer according to the input adaptation data set, and wherein measuring the adaptation images comprises scanning the printed adaptation patches using an in-line scanner of the printer to generate the measured adaptation data set.
11. The method of claim 9 , wherein adapting the parametric forward color transform comprises fitting a polynomial surface to the adaptation data.
12. The method of claim 1 , wherein the input initial characterization data set is homogeneously sampled with respect to a regular grid in the first color space.
13. A color processing device, comprising:
a rendering system operative to produce a visible image according to input color data in a first color space;
a system controller operative to provide the input color data to the rendering system according to a print job;
a sensor operative to generate measured data in a second color space representative of the visible image; and
a characterization system coupled with the system controller and the sensor and operative to cause the rendering system to produce a plurality of visible color images according to an input initial characterization data set, to receive a measured initial characterization data set representative of the color images from the sensor, to generate a parametric forward color transform using the input initial characterization data set and the measured initial characterization data set, to generate an estimated initial characterization data set using the parametric forward color transform and the input initial characterization data set, to generate a nonparametric forward color transform using the measured and estimated initial characterization data sets, and to construct a forward color transform for the device using the parametric and nonparametric forward color transforms.
14. The color processing device of claim 13 , wherein the rendering system comprises a plurality of marking devices operative according to the input initial characterization color data to transfer marking material onto a corresponding medium to create visible color images on the medium, and wherein the sensor is a scanner operative to scan the medium and to generate measured initial characterization data representative of the printed visible color images.
15. The color processing device of claim 14 , wherein the characterization system is operative to adapt the nonparametric forward color transform.
16. The color processing device of claim 15 , wherein the characterization system is operative to cause the rendering system to produce a plurality of visible adaptation images on the medium according to an input adaptation data set in the first color space, to receive a measured adaptation data set representative of the adaptation images from the scanner in the second color space, and to adapt the parametric forward color transform using the input adaptation data set and the measured adaptation data set.
17. The color processing device of claim 16 , wherein the scanner is integrated into the rendering system.
18. The color processing device of claim 16 , wherein the characterization system is operative to fit a polynomial surface to the adaptation data to adapt the parametric forward color transform.
19. The color processing device of claim 13 , wherein the rendering system comprises a display.