Abstract: Certain examples described herein relate to the control of colorants and treatments for printing. In certain examples image data, a colorant color mapping and one or more treatment color mappings is obtained. The colorant color mapping may be used to map the image data to colorant application values. The one or more treatment color mappings may be used to map the image data to treatment application values. The colorant application values and treatment application values may be used to generate discrete print control instructions to apply the set of colorants and set of treatments to a printing substrate.

Abstract: A method is disclosed. According to some examples, the method comprises determining, by processing circuitry, a first element set to be associated with a print addressable location, the first element set comprising a first plurality of elements, wherein each element of the first plurality of elements identifies a print colorant or print colorant combination and is associated with a probability that the print colorant or print colorant combination identified by that element is to be applied to the associated print addressable location.

Abstract: Certain examples described herein relate to adjusting a printing system. In certain cases, a lookup table, LUT, is obtained where the lookup table comprises a plurality of nodes that map a plurality of input first color space values to a plurality of Neugebauer Primary area coverage, NPac, vectors in a second color space and each NPac vector comprises at least one Neugebauer Primary, NP. Each NPac vector in the LUT is adjusted by the determination of a colorimetric value of the NPac vector and the modification of the NPac vector based on a characteristic of the corresponding at least one NP and the colorimetric value such that the modification is specific to the NPac vector. The lookup table is updated with the modified NPac vector and stored for referral by the printing system in any future printing.

Abstract: In an example, a method includes determining, using processing circuitry, a first print coverage vector associated with an estimated colorimetry which corresponds to a target colorimetry, wherein the estimated colorimetry of the print coverage vector is based on a first color model, the first print coverage vector being optimised relative to a first metric. The method may further include determining, using processing circuitry, a predicted colorimetry of the first print coverage vector based on a second color model.

Abstract: A method is described in which sets of corresponding colorimetric values are obtained. In a set, a colorimetric value is associated with a device color. A number of device colors are selected according to the color differences between colorimetric values associated with the same device color. A color calibration pattern is elaborated for a printer to be calibrated using the selected device colors and calibration is performed using the sets of colorimetric values.

Abstract: In an example, a method includes obtaining, by a processor, a first set of vertices of a set of simplexes defining a hull of an initial color gamut. A value representing a size of a first simplex of the set of simplexes may be determined and compared to a first threshold. When the determined value is less than the first threshold, at least one vertex of the first simplex may be removed from the first set of vertices to determine a modified color gamut hull.

Abstract: Certain examples relate to a method of color prediction. Data indicative of color characteristics measured from a number of color test patches is obtained. Data indicative of combinations of color resources used to render the color test patches on a color rendering device is obtained. A first predictive model is trained using the data indicative of the combinations of color resources as an input and corresponding data indicative of color characteristics as ground truth outputs. A second predictive model is trained using the output data from the first predictive model as an input and the corresponding data indicative of color characteristics as ground truth outputs. A progressive mapping is implemented by the first and second predictive models to predict color characteristics rendered by the color rendering device given a combination of color resources.

Abstract: A method is described in which a reflection is obtained of a laser light pattern reflected from a substrate. A reflection of diffuse light may be obtained from the substrate. A first parameter may be determined, relating to the substrate from the reflected laser light pattern. A second parameter may be determined, relating to the substrate from the reflected diffuse light and a characteristic of the substrate may be determined from the first and second parameters. A print apparatus and a machine-readable medium are also disclosed.

Abstract: A print calibration system comprising a printing device to apply print material to a print target in a printing process, a memory for storing a lookup table; and a processor. The processor causes the printing device to print calibration points for reproducing a color ramp, by receiving a plurality of Neugebauer Primary area coverage (‘NPac’) points representing the plurality of calibration points and determining a hue angle and color space based on the NPac points. A plurality of nodes distributed between a first node and a second node of a sectional representation of the NPac points is determined. A lookup table is generated based on a relationship between the plurality of nodes and the NPac points for use during the printing process, wherein the lookup table comprises values to map between a first color space and a second color space, the lookup table is then provided to the printing device.

Abstract: Disclosed is an apparatus generate updated sets of printing parameters for a printing process, the apparatus comprising a processor to receive initial correspondence data indicating correspondence between a plurality of color values and respective sets of printing parameters, wherein at least one colorant combination and a respective coefficient is assigned to each of the sets of printing parameters. The processor is to assign a weight to each colorant combination in the initial correspondence data based on at least a printing quality criterion relating to the colorant combinations within the initial correspondence data, and re-assign colorant combinations and respective coefficients to generate updated sets of printing parameters based on the assigned weights. Also disclosed is a method and a non-transitory computer readable storage medium.

Abstract: A print calibration system comprising a printing device to apply print material to a print target in a printing process, a memory for storing a lookup table; and a processor. The processor causes the printing device to print calibration points for reproducing a color ramp, by receiving a plurality of Neugebauer Primary area coverage (‘NPac’) points representing the plurality of calibration points and determining a hue angle and color space based on the NPac points. A plurality of nodes distributed between a first node and a second node of a sectional representation of the NPac points is determined. A lookup table is generated based on a relationship between the plurality of nodes and the NPac points for use during the printing process, wherein the lookup table comprises values to map between a first color space and a second color space, the lookup table is then provided to the printing device.

Abstract: Certain examples described herein relate to adjusting a printing system. In certain cases, a lookup table, LUT, is obtained where the lookup table comprises a plurality of nodes that map a plurality of input first color space values to a plurality of Neugebauer Primary area coverage, NPac, vectors in a second color space and each NPac vector comprises at least one Neugebauer Primary, NP. Each NPac vector in the LUT is adjusted by the determination of a colorimetric value of the NPac vector and the modification of the NPac vector based on a characteristic of the corresponding at least one NP and the colorimetric value such that the modification is specific to the NPac vector. The lookup table is updated with the modified NPac vector and stored for referral by the printing system in any future printing.

Abstract: A method is described in which a reflection is obtained of a laser light pattern reflected from a substrate. A reflection of diffuse light may be obtained from the substrate. A first parameter may be determined, relating to the substrate from the reflected laser light pattern. A second parameter may be determined, relating to the substrate from the reflected diffuse light and a characteristic of the substrate may be determined from the first and second parameters. A print apparatus and a machine-readable medium are also disclosed.

Abstract: Certain examples described herein relate to color calibration. In certain cases, a plurality of test patches are printed with a printing system, the test patches corresponding to a set of initial color sample points and a set of test colors. Color properties of the printed test patches are measured. In certain examples, a gamut descriptor is identified from a plurality of gamut descriptors using the color properties of the test colors. Each gamut descriptor defines a set of up-sampling parameters for a particular color gamut. Measured color properties for the initial color sample points are up-sampled using the set of up-sampling parameters for the identified gamut descriptor to generate up-sampled data. In certain cases, the up-sampled data is used to generate a color mapping to be applied to print job data received by the printing system.

Abstract: A method of obtaining a calibration factor for color calibration of a printing system. The method includes printing, using the printing system, a plurality of Neugebauer primaries (NPs) each defined by a respective Neugebauer primary area coverage (NPac) vector. For each of the NPs, an area coverage change of the NP is determined from a measurement of a visual property for the NP and a measurement of the visual property for a corresponding reference NP corresponding to the respective NPac vector. The calibration N factor for the printing system is obtained based on the area coverage change for respective NPs of the plurality of NPs.

Abstract: A method of detecting printing fluid mixing is provided. A test pattern for at least one printing fluid is printed with a printing device. The test pattern for the at least one printing fluid is scanned with a scanning device. Colorimetric data of the test pattern for the at least one printing fluid are obtained. Metric values are determined from the colorimetric data. A statistical analysis is performed on the determined metric values. Based on the statistical analysis, it is determined whether printing fluid mixing has occurred and where printing fluid mixing has occurred.

Abstract: A method of calibrating a printing system. Data defining a color mapping that maps a first set of n-dimensional color Input points to a corresponding second set of n-dimensional color output points, the color mapping representing a measured behavior of the printing system, is obtained. A smoothed mapping function of color input points that satisfies a predetermined optimization condition based on a mapping error between the smoothed mapping function and the color mapping is determined. The mapping error is a function of individual errors between outputs of the smoothed mapping function as applied to respective color input points in the first set of color input points and corresponding color output points from the second set of color output points as mapped from the respective color input points by the color mapping. The smoothed mapping function is used to calibrate the printing system.

Abstract: An apparatus and method for use in generating calibration parameters for a printing apparatus comprising a plurality of print modules are disclosed. The method comprises printing a first plurality of test patches for each print module of the plurality of print modules, analysing the first plurality of test patches to identify at least two clusters of print modules, wherein each cluster comprises a sub-group of print modules having substantially similar performance, printing a second plurality of test patches comprising an extended calibration test patch set for each cluster of print modules, the second plurality of test patches being distributed across the print modules of the cluster, and analysing extended calibration test patch set for each cluster to determine a calibration parameter for the printing apparatus.

Abstract: Certain examples described herein relate to color calibration. In certain cases, a plurality of test patches are printed with a printing system, the test patches corresponding to a set of initial color sample points and a set of test colors. Color properties of the printed test patches are measured. In certain examples, a gamut descriptor is identified from a plurality of gamut descriptors using the color properties of the test colors. Each gamut descriptor defines a set of up-sampling parameters for a particular color gamut. Measured color properties for the initial color sample points are up-sampled using the set of up-sampling parameters for the identified gamut descriptor to generate up-sampled data. In certain cases, the up-sampled data is used to generate a color mapping to be applied to print job data received by the printing system.

Abstract: A method of calibrating a printing system. Data defining a color mapping that maps a first set of n-dimensional color Input points to a corresponding second set of n-dimensional color output points, the color mapping representing a measured behavior of the printing system, is obtained. A smoothed mapping function of color input points that satisfies a predetermined optimization condition based on a mapping error between the smoothed mapping function and the color mapping is determined. The mapping error is a function of individual errors between outputs of the smoothed mapping function as applied to respective color input points in the first set of color input points and corresponding color output points from the second set of color output points as mapped from the respective color input points by the color mapping. The smoothed mapping function is used to calibrate the printing system.