Abstract: At least a portion of a 3-D object is converted into a format suitable for printing. A material volume coverage vector for each voxel of a 3-D bit map of a 3-D object is determined. The 3-D bit map comprises a plurality of voxels, each voxel located at a unique 3-D location. A rectangular cuboid comprising an M×N×L array of voxel locations enclosing at least a portion of the 3-D object is determined. A halftone threshold matrix comprising an array of threshold values is provided. The halftone threshold matrix is converted to provide an M×N×L 3-D array of threshold values. Each material volume coverage vector of the at least a portion is compared with each threshold value at corresponding 3-D locations to select a printable voxel at each 3-D location to convert the at least a portion of the 3-D object into a format suitable for printing.

Abstract: Certain examples described herein relate to apparatus arranged to produce a three-dimensional object. These examples enable color and material properties of such an apparatus to be characterized. This is achieved through the generation of configuration data for the apparatus that maps at least one color property to one or more material volume coverage vector values. This allows for appropriate quantities of materials available to the apparatus to be used to produce colors defined in received object data for the three-dimensional object.

Abstract: Certain examples described herein relate to a three-dimensional threshold matrix. The three-dimensional threshold matrix may be used for three-dimensional halftoning. In one example, values for a predefined two-dimensional threshold matrix are shifted with respect to a third dimension to provide the three-dimensional threshold matrix. In one example, the three-dimensional threshold matrix may then be processed in association with a digital representation of a three-dimensional object to output discrete material arrangement instructions for at least one production material. The instructions may be used to control an additive manufacturing system to produce the three-dimensional object.

Abstract: Methods and apparatus relating to substructures for three-dimensional objects are described. In an example, a method comprises receiving a lattice model having a consistent dimensionality and determining a substructure model representing a three-dimensional material structure, the substructure model being based on the lattice model and specifying a variable material distribution. The substructure model may be populated with halftone threshold data to provide a three-dimensional halftone threshold matrix.

Abstract: A system includes a memory to store at least one Halftone Area Neugebauer Separation (HANS) look-up table (LUT) that represents a predetermined drop weight for N colorant channels of a printer. The HANS LUT provides a given Neugebauer Primary area coverage in response to a device color input value. Measurement data stored in the memory represents measured drop weight values for the N colorant channels of the printer. A processor executes instructions stored in the memory. The instructions are to compute a calibration element for the HANS LUT that describes a drop-weight deviation with respect to the HANS LUT based on the measured drop weight values. The instructions are to apply the calibration element to at least a portion of the HANS LUT to generate a calibrated LUT.

Abstract: A method of generating a set of halftone parameters. The method comprises assigning a first set of halftone parameters to a first location in a color space, the first location in the color space corresponding to a first color, and assigning a second set of halftone parameters to a second location in the color space, the second location in the color space corresponding to a second color. An interpolating between the first set of halftone parameters and the second set of halftone parameters is performed, based on the first location and the second location, to determine a third set of halftone parameters corresponding to a third location in the color space. The result of the interpolation is output data associating the third set of halftone parameters with a third color corresponding to the third location in the color space.

Abstract: Methods and apparatus relating to three-dimensional object models are described. In one example, (i) data representing a geometrical description of a three-dimensional object defining object geometry in a geometric space and (ii) at least one object property description describing an object property in an object property space are received. The object property space and the geometric space are intersected to define an object model, wherein an object property is defined at an intersection between a described object property and defined object geometry.

Abstract: Certain examples for generating control data for production of a three-dimensional object are described. In one example, the three-dimensional object to be generated is represented using object model data and object property data. This data is processed to generate a rasterized representation of a plane of the three-dimensional object. The rasterized representation of the plane is then mapped to an area coverage representation defines object property data at a given location in the plane as one or more proportions of a set of available object properties at the location, for example material combinations. The area coverage representation is then halftoned to generate the control data for three-dimensional printing.

Abstract: A system includes a memory to store pre-computed boundary look-up tables (LUTs) for respective drop weight boundary classes of a printer having a plurality of colorants. Each pre-computed boundary LUT provides one Neugebauer Primary area coverage (NPac) for each node of the LUT in response to a device color input value that corresponds to each node. Measurement data stored in the memory represent measured drop weight values for the plurality of different colorants of the printer. A processor executes instructions that interpolate among the pre-computed LUTs based on the measured drop weight values to determine a proportional weighting of each of the pre-computed LUTs.

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: In an example, a method includes identifying, within data for use in printing, a first element set associated with a first print addressable area, wherein elements of the element set are each associated with a print instruction. An element may be selected from the first element set and assigned to the first print addressable area. A second print addressable area may be identified as a candidate print addressable area for error diffusion, the second print addressable area being associated with a second element set. An error associated with the selection of the element from the first element set is scaled based on a criterion and may be diffused to elements of the second element set.

Abstract: An example method of setting ink limits for a printing system is described. The method involves printing a first set of color ramps. Each color ramp has test areas which are printed based different Neugebauer Primary Area Coverage (NPac) vectors. A test area for each color ramp is indicated that meets an image quality metric and Neugebauer Primary ink use limits are set based on these test areas. A second set of color ramps, for combinations of the set of available Neugebauer Primaries, is then printed, The test areas for each ramp are defined by monotonically-varying vector element values for one Neugebauer Primary in a combination and the second set of ramps are defined by monotonically-varying vector element values across said ramps for another Neugebauer Primary in a the combination. Test areas are then indicated again for the second set of color ramps to set ink use limits for the printing system.

Abstract: In an example, a method for generating control data for production of a three-dimensional object is described. A model of the three-dimensional object is obtained as a array of voxels, and it is determined for each voxel whether that voxel comprises part of a first or a second sub-object of the three-dimensional object. Each first sub-object voxel is mapped to a volume coverage representation defining print material data for that voxel. The second sub-object voxels are mapped to a volume coverage representation defining common print material data for the voxels of second sub-object. Control data for printing the first sub-object is generated from the print material data for that voxel common print material data for the Control data for printing the second sub-object is generated according to the volume coverage representation for the second sub-object.

Abstract: Methods and apparatus relating to representation of a three-dimensional object are described. In an example, a converter for converting input object data representing a model of a three-dimensional object into a compressed form is provided. The converter comprises a data receiving module to receive data representing object properties of a three-dimensional object to be generated by additive manufacturing apparatus and a data identifying module to identify data representing a continuous region of the object with a common property specification. The converter further comprises a sub-region defining module to determine, within the data representing the continuous region, a set of contiguous sub-regions and an object data module to represent the continuous region as the set of sub-regions.

Abstract: A method is described in which printing instructions representing printing content to be printed by a printing system are received, the printing system comprising a dispenser to dispense printing material. Whether to perform a first mapping process or a second mapping process is then selected. The first mapping process comprises mapping an indicator to a first dispensing process to dispense printing material from the dispenser to produce content according to a content characteristic of the printing content at a given location, and the second mapping process comprises mapping the indicator to a second dispensing process to dispense printing material to produce content according to the content characteristic at the given location. The first dispensing process is different than the second dispensing process. The indicator represents the content characteristic. The method also comprises performing the selected mapping process.

Abstract: A method is described in which data representing a three-dimensional object to be printed is obtained. The data comprises object property data indicative of properties of the three-dimensional object. Layers within the three-dimensional object to be printed are identified. The obtained data is processed by comparing object property data associated with an identified layer to object property data associated with a reference layer selected from the identified layers. Where a difference in object property data associated with an identified layer and object property data associated with a reference layer is determined, the determined difference is stored.

Abstract: An example method involves analyzing a plurality of perturbations of a printing system over a period of time, calculating statistics corresponding to each of the plurality of the perturbations of the printing system, after the duration of the period of time, executing an enhancement process for the printing system based on the calculated statistics of each of the perturbations, and adjusting settings of the printing system based on results of the enhancement process.

Abstract: According to examples, area coverage vectors for each pixel on each slice of a digital representation of an object may be determined and a two-dimensional halftone matrix including threshold values may be subdivided into a plurality of sub-matrices, each sub-matrix including threshold values of the halftone matrix in a respective value sub-range. In addition, for each of the slices, a sub-matrix of the plurality of sub-matrices may be selected and the area coverage vectors for the pixels in the slice may be halftoned using respective threshold values of the selected sub-matrix.

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: Certain examples described herein relate to producing three-dimensional objects using additive manufacturing systems. These examples combine the use of material volume coverage vectors to define object data with octree data structures and models for tracking material placement error and available volumes. Material volume coverage vectors correspond to a volumes of three-dimensional objects and define a probabilistic distribution of materials available to an additive manufacturing system including combinations of said materials. In certain examples, a bottom level of the error tracking octree model is constructed to contain at least a portion of the data values for a set of obtained material volume coverage vectors. This is then used in an error distribution process to generate manufacturing control data for the additive manufacturing system.