Abstract: Generation of an Interim Connection Space (ICS) of a full spectral space is provided. A space of illuminants is accessed, and the full spectral space is decomposed into a first subspace that is an orthogonal complement of a metameric black subspace for the space of illuminants. The Interim Connection Space is generated based on the first subspace. The generated ICS can be used, for example, for rendering an image on an additive color destination device. One image rendering workflow includes accessing color data of the image in an ICS, transforming the color data from the ICS into a device dependent color space of an additive color destination device, and rendering the transformed color data on the destination device.

Abstract: Generation of an Interim Connection Space for spectral data in a full spectral space is provided. A set of linear maps is accessed, each linear map characterizing a linear transformation from the full spectral space to a colorimetric space, and spectral measurement data is accessed. The linear maps can for example be determined by a set of illuminants. The full spectral space is decomposed into a first subspace that minimizes a loss of a spectral component in the spectral measurement data under a projection along a second subspace onto the first subspace. The second subspace is a null subspace of the set of linear maps. The Interim Connection Space is generated based on the first subspace. The Interim Connection Space can include, for example, a linear map characterizing a linear transformation from the Interim Connection Space to the full spectral space, and a linear map characterizing a linear transformation from the full spectral space to the Interim Connection Space.

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 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: An improvement to sigmoidal gaussian cusp knee (SGCK) gamut mapping algorithm useful for gamut boundary descriptors (GBDs) that are defined with multiple shells rather than a single hull. The gamut mapping algorithm involves a lightness-rescaling step and a chroma compression step, in which points on each of the shells of the source GBD are mapped to corresponding points on the respective shells of the destination GBD. In situations where there is a mismatch between the number of shells in the source GBD and the destination GBD, such as a case where one of the GBDs is defined by a singly-shelled GBD whereas the other is defined by a two-shelled GBD, an induced hue slice may be constructed so as to simulate the missing shell. In addition, an induced hue slice may be constructed in a situation where lightness rescaling results in a mapping that is too steep between source and destination.

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: 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 method and apparatus for determining a grid structure for a set of values in a device color space is provided. A multi-step process applies heuristics to a collection of color sample data in order to determine the structure of a look-up table that best fits the samples. A first step is a sorting and counting step, in which the sampling data is sorted for each channel, and the number of steps in each channel is counted. A second step is a check for completeness of the data. A third step is a removal step in which steps are removed if they do not correspond to steps on the axes of the three-dimensional cube. The fourth step is a check for a full Look Up Table (LUT). If a full LUT has been obtained, then the structure of the LUT has been determined and the process ends. On the other hand, if the check for a full LUT is unsuccessful, then a fifth step is performed, in which steps are removed if they are under-correlated with other steps.

Abstract: Generation of basis functions for spectral reflectances of color samples is provided. Reflectance information of the color samples is input, the reflectance information is weighted with a weighting function based on a wavelength dependence of an optical sensor, and the weighted information is analyzed to obtain the basis functions. Basis functions for illuminants are generated by inputting reflectance and associated information of the color samples, inputting illuminant information, constructing a matrix of weighted tristimulus values, and analyzing the matrix to obtain the basis functions. A weighting function for an optical sensor is generated by inputting a first weighting function, based on transformation of a reflectance perturbation from a reflectance space into a color space of the sensor, calculating the first weighting function with predetermined stimuli to obtain a plurality of resulting functions, and averaging the resulting functions to obtain the weighting function for the sensor.

Abstract: The present invention provides for gamut mapping between a source device and a destination device, the destination device having a destination device black point with a hue, and the source device and the destination device being respectively characterized by a source gamut shell and a destination gamut shell. A lightness compression is performed using the source gamut shell, the destination gamut shell and the destination device black point. A constant lightness transformation is performed, wherein the constant lightness transformation modifies the destination gamut shell so that a shell boundary of the destination gamut shell on the hue plane containing the destination device black point is shifted from an original position to align with a neutral axis of the destination gamut shell. A chroma compression is performed using the source gamut shell and the modified destination gamut shell.

Abstract: A method and apparatus for inverting a color device model. A systematic color device model inversion process restarts a local iterative root finding process with new seeds that are adaptive to the last found solution. Because of the relative simplicity of the logic used, it is more robust and makes less assumptions about the smoothness of the forward model. It is also computationally inexpensive, because a reasonably good seed is chosen from the seed matrix using a fast calculation of distance, instead of running each seed in the seed matrix through the iterative root finding process. In the worst case, including the initial run, N+1 runs of the local iterative root finding process are needed to invert an input point, with N being the number of additional, a posteriori seeds generated.

Abstract: The present invention provides for gamut mapping between a source device and a destination device, the destination device having a destination device black point with a hue, and the source device and the destination device being respectively characterized by a source gamut shell and a destination gamut shell. A lightness compression is performed using the source gamut shell, the destination gamut shell and the destination device black point. A constant lightness transformation is performed, wherein the constant lightness transformation modifies the destination gamut shell so that a shell boundary of the destination gamut shell on the hue plane containing the destination device black point is shifted from an original position to align with a neutral axis of the destination gamut shell. A chroma compression is performed using the source gamut shell and the modified destination gamut shell.

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.

Abstract: Construction and use of an inner shell for a multi-shelled gamut boundary descriptor (GBD) for a source device based on a predesignated outer shell for the source device, for use in gamut-mapping from the gamut of the source device to a gamut of a destination device. An inner shell and outer shell for the destination device is accessed, and a determination is made of an amount by which the inner shell of the destination device is smaller than the outer shell of the destination device. The inner shell of the source device is thereafter constructed by reducing the outer shell of the source device based at least in part on the amount by which the inner shell of the destination device is smaller than the outer shell thereof. The construction can be performed on the entirety of the GBD or only on parts thereof, such as a hue slice.

Abstract: Construction and use of a multi-shelled gamut boundary descriptor for an RGB display device in which one shell is an outer “plausible” shell and another shell is an inner “reference” shell. The outer shell is coterminous with a unit RGB cube. The inner shell is constructed based on eight reference primaries in the RGB cube, corresponding to primary colors black, blue, green, cyan. red, magenta, yellow and white. Both the inner cube and the outer cube in RGB color space are transformed to a perceptual color space, thereby defining the GBDs for an inner and an outer shell of a multi-shelled GBD.

Abstract: An improvement to sigmoidal gaussian cusp knee (SGCK) gamut mapping algorithm useful for gamut boundary descriptors (GBDS) that are defined with multiple shells rather than a single hull. The gamut mapping algorithm involves a lightness-rescaling step and a chroma compression step, in which points on each of the shells of the source GBD are mapped to corresponding points on the respective shells of the destination GBD. In situations where there is a mismatch between the number of shells in the source GBD and the destination GBD, such as a case where one of the GBDs is defined by a singly-shelled GBD whereas the other is defined by a two-shelled GBD, an induced hue slice may be constructed so as to simulate the missing shell. In addition, an induced hue slice may be constructed in a situation where lightness rescaling results in a mapping that is too steep between source and destination.

Abstract: The present invention provides for a performing a type of gamut operation for a color device given a color input value, the color device being characterized by a gamut boundary comprising a collection of gamut boundary triangles. Boundary line elements are determined that correspond to a subset of the collection of gamut boundary triangles. The subset of the collection of gamut boundary triangles does not include gamut boundary triangles which are unlikely to yield useful results based on the type of gamut operation and the color input value. Each boundary line element represents a line segment defined by an intersection of one of the gamut boundary triangles within the subset of the collection of gamut boundary triangles with a hue plane, and the hue plane is within the gamut boundary and based on the color input value. In addition, a result is determined for the gamut operation using one or more of the determined boundary line elements.

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: 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: A method and apparatus for color conversion useful for color devices having a large number of input channels, for example CMYK color printers having additional inks used to enhance the color printer's gamut. The color conversion is performed using a strata collection of look-up tables that stratify an n-dimensional color space into sets of lower dimensional subspaces. For lower dimension subspaces, the associated look-up tables may be closed, while for a higher dimension subspace, an associated look-up table may be open, leaving gaps in the subspace not enclosed by a look-up table. A color management module using the strata collection for color conversion may determine if a color conversion is for a color value that falls within a gap. If so, the color management module may use a relatively complex interpolation process. If not, the color management module may use a relatively simple interpolation process.