Abstract: A method and apparatus for interpolating values for a color space from an input color value. A unit hypercube enclosing the input value is generated based on values from a look up table. A set of boundary conditions are then imposed on the unit hypercube. To perform the actual interpolation, an initial barycentric projection is performed from a selected vertex of the unit hypercube through the input value onto a boundary of the unit hypercube. If the projection satisfies one of the boundary conditions, an interpolated value is calculated using the projection by back substitution. If the initial projection does not satisfy a boundary condition, an intermediate value is generated from the previous projection and successive barycentric projections are performed using respectively different vertices of the unit hypercube through intermediate values onto a boundary of the unit hypercube until a projection satisfies one of the boundary conditions.

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.

Abstract: A method for correcting a color value generated by a forward model for a color input device. A color value generated by the forward model is mapped into a color space. The color value is clipped to a locus of a visual gamut in the color space if the color value falls outside of the visual gamut. Clipping the mapped color value ensures that the color input device generates color values that represent colors within the human visual system. Clipping may be accomplished by clipping a color value to an intersection of a locus boundary and a vector between the color value and a white point. The locus used may be the CE spectral locus projected into the color space. Any number of standard color spaces may be used in the method, such as CIEXYZ, CIELUV, or CIELAB.

Abstract: The present invention provides a method for characterizing display devices. Initially, a plurality of colors are generated on the display device. The generated colors are measured and a black point and a white point are determined. The measured colors are then corrected for the determined black point in order to obtain a plurality of chromaticity values. The chromaticity values of the corrected color values are averaged, and a tristimulus matrix is generated with the averaged chromaticity values and the determined white point. By averaging the chromaticity values of black-point-corrected measurements, the present invention is able to create more accurate display device characterizations that account for the effects of flare. In addition, by averaging the chromaticity values of black-point-corrected measurements, the present invention minimizes the effects of inaccurate color measurements made during the device characterization process.

Abstract: 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.

Abstract: The present invention creates a color transform for transforming color image data from a device-independent color space to a device-dependent color space of a color device. A forward model is accessed which transforms color image data from the device-dependent color space to the device-independent color space. The forward model is iteratively inverted to obtain a plurality of distinct device-dependent data point value sets, wherein the device-dependent data point value sets are colorimetrically identical to each other in the device-independent color space. One device-dependent data point value set is then selected from the plurality of distinct device-dependent data point value sets based on the application of a color purity function to the plurality of distinct device-dependent data point value sets. The color transform is populated with the selected device-dependent data point value set.

Abstract: A color characterization process utilizing nonlinear regression analysis to characterize a color input device. The color input device is used to generate a bitmap of device dependent values from a color target. The bitmap of device dependent color values is used to generate a forward model that maps device dependent color values to color values in a device independent color space using a nonlinear regression analysis that minimizes a color difference metric between the reference color values and the set of device dependent color values mapped through the forward model. The color difference metric is chosen to represent human perceived color differences in the device independent color space. The performance of the nonlinear regression analysis may be improved by initializing the nonlinear regression analysis using an initial forward model generated from a linear regression analysis.

Abstract: Creating a look-up table which converts color image data from a device-independent color space to a device-dependent color space, by determining a range of lightness values corresponding to a lightness value of a target data point in device-independent color space, searching a predetermined set of data points in device-independent color space to obtain a selected set of data points, each selected data point having a lightness value within the determined range of lightness values and having corresponding device-dependent component values within a predetermined tolerance level of the component values of a previously-determined device-dependent data point, performing a weighted interpolation on the device-dependent component values corresponding to the selected set of data points to calculate an interpolated data point which is in device-dependent color space, and entering the interpolated device-dependent data point into a look-up table entry corresponding to the device-independent target data point.