Raster Image Processor

Abstract

A raster image processor (RIP) for digitally binary half-toning a continuous tone image (CT) into a half-tone raster image (RT) by means of a threshold tile (TT) for enabling the display of the image on multiple substrates (S1, S2, ..., S M ) printing device; wherein the processor includes an input field, wherein information about the substrate to be used; a memory, on which a plurality of threshold blocks (TT1, TT2, ..., TT N ); and a threshold selector capable of selecting the plurality of threshold tiles (TT1, TT2, ..., TT2) based on information provided to the input field N ) in the threshold tile (TT).

Description

Technical Field

[0001] The present invention relates to the field of raster image processors (RIPs) for digitally halftoning continuous tone images and in particular for printing images by means of lithographic or flexographic printing presses. Background Art

[0002] Printing presses and digital printers cannot vary the amount of ink or toner applied to a particular image area except through digital halftoning, also known as dithering or screening. Digital halftoning is the process of rendering the illusion of a continuous tone image using multiple dots (also known as halftone dots). The digital image produced by digital halftoning is called a halftone raster image or screen. Both multi-level and binary halftoning methods are known. The halftone dots produced by the binary method consist of pixels representing image data and pixels representing non-image data.

[0003] Binary digital halftoning is a well-known technique, which is explained in detail by Robert Ulichney in his book "Digital Halftoning" (MIT Press, 1987, ISBN 0-262-21009-6), where Chapter 5 on "Ordered Dithering of Centralized Dots" is the background technology for the present invention, including the use of threshold tiles to render continuous tone images.

[0004] Another overview of digital halftoning methods is disclosed in the article "Recent trends in digital halftoning" (Proc. SPIE 2949, Imaging Science and Display Technology, (February 7, 1997); doi: 10.1117 / 12.266335), in which multi-level digital halftoning is also explained.

[0005] The digital halftoning method is implemented by a raster image processor (abbreviated as RIP). The processor (RIP) converts an electronic document mainly defined in a page description language (PDL) into a continuous tone image (CT), and halftones the image in a halftone raster image (RT) for printing. A well-known page description language (PDL) is PostScript TM (PS) and "page description format" (PDF). The processors are mainly prepress workflow systems (such as Apogee from manufacturer AGFANV TM ) in the kernel.

[0006] AM (Amplitude Modulation) screening is a widely used centralized dot ordered dithering technique, in which the size of the halftone dots is modulated to represent different densities of the image. The halftone dots are tiled regularly according to the screening frequency and the screening angle. AM halftone dots are usually circular, oval, diamond or square.

[0007] But recently other types of regularly tiled halftone dots have become available, such as from Esko TM Concentric circle screening, as disclosed in US2007 / 0002384, where the halftone dots have a shape with one or more rings, or more recently multi-centered halftone dots as disclosed in EP3461116. However, both involve complex mathematics and difficult calibration, and therefore cannot be implemented on a widespread installed base of prepress workflow systems with limited data storage and / or processing capabilities.

[0008] Another type of regular halftone dots is disclosed in application WO 2019 / 081493 A1 (AGFANV), namely spiral halftone dots, which can be implemented with a single threshold tile, such as in AM screening.

[0009] US2008123146 A1 (RICOH COMPANY LTD) discloses a dither matrix for use in halftone processing to convert input image data having M input halftone levels into output image data having N (M>N>2) output halftone levels, thereby using a multi-level halftone process. Fig.10 There are three described halftoning methods, which are implemented in a raster image processor according to the image object type in the literature: a character dithering step for characters; a graphic dithering step for lines and graphics and an error diffusion step for images.

[0010] Print quality is achieved by controlling the halftoning process in the Raster Image Processor (RIP). But to achieve high quality printing on the selected substrate, it is important to use the appropriate threshold tiles to halfton the continuous tone image (CT). For printing on multiple substrates (S1, S2, ..., S M ), the operator selects the threshold tile for halftoning based on experience and his own feeling, depending on the substrate to be printed. However, as discussed above, the number of halftone dot shapes and their variations are growing recently. When the processor has the number of halftone dot shapes available, it occasionally happens that an inappropriate halftone dot shape is selected to print the selected substrate (S i ) is halftoned. This results in a printed image on the selected substrate not being provided as intended. Summary of the invention

[0011] The present invention aims to provide a raster image processor (RIP) for digitally half-toning a continuous tone image (CT) into a half-tone raster image (RT) for being able to be displayed on a plurality of substrates (S1, S2, ..., S M ) is a printing device printed on a substrate. The processor has several advantages, such as providing a threshold selection method for automatically selecting a threshold tile suitable for a selected substrate. If the threshold tile (TT1, TT2, ..., TT N ) is large, the selection makes it easier for the operator, especially when the threshold blocks determine a large number of halftone dot shapes, including variations in said shapes, and especially when said shapes include variations that seriously affect the print quality. Thus N is greater than 2.

[0012] This problem is solved by the method disclosed in the present invention, wherein the processor comprises an input field, wherein information about the substrate to be used, preferably a substrate from the plurality of substrates, and a memory having stored thereon a plurality of threshold tiles (TT1, TT2, ..., TT N ); and a threshold selector capable of selecting the plurality of threshold tiles (TT1, TT2, ..., TT N ) in the threshold tile (TT). For example, a selected threshold tile may be selected because it gives less pattern, less / more gloss, less ink usage and / or less light transmission when used for halftones and representing continuous tone images on a selected substrate.

[0013] The processor apparently manages a plurality of threshold tiles stored in a memory and selects therefrom the most effective threshold tile for use with a selected substrate. The processor also has means for receiving a continuous tone image (CT); and means for storing the continuous tone image (CT) in another memory.

[0014] The regularly tiled halftone dots are preferably arranged according to a screening frequency greater than 100 lines per inch, and more preferably arranged according to a screening angle selected from the group consisting of 0°, 7.5°, 15°, 22.5°, 75°, 45°, 67.5° and 82.5°.

[0015] In a preferred embodiment, the processor additionally comprises: an ink usage predictor; and wherein the threshold selector is capable of selecting a threshold tile (TT) additionally based on a predicted amount of ink from the ink usage predictor; wherein the amount is selected by a plurality of threshold tiles (TT1, TT2, ..., TT N) is calculated from a halftone raster image of a continuous tone image (CT). The amount can be described in milliliters or in ink layer thickness.

[0016] The ink usage predictor is able to predict the amount of ink from a selected halftone raster image that should be printed on a substrate. The calculation is based on complex mathematics, as further disclosed in the examples. The selection of the most effective threshold tile may be the one with the lowest ink amount prediction.

[0017] The type of ink used to render the continuous tone image also affects the print quality, for example, inks that must be cured or inks that have high penetration in the chosen substrate. Q ) printing, the raster image processor (RIP) preferably further comprises another input field, wherein information relates to the ink to be used, preferably an ink from the plurality of inks; and wherein the threshold selector is capable of determining the threshold tile (TT) additionally based on the information provided to the other input field.

[0018] The preferred processor manages a plurality of threshold tiles stored in memory and selects therefrom a most effective threshold tile for a selected substrate in combination with a selected ink.

[0019] It is found that certain halftone dots may be varied more than AM screening to optimize the printing quality on the selected substrate, such as affecting the amount of ink. In a preferred embodiment, the plurality of threshold blocks (TT1, TT2, ..., TT N )include

[0020] a) A set of threshold tiles for generating a halftone image, wherein at least a portion of all halftone cells are halftone dots comprising:

[0021] (i) image pixels arranged as a first cluster or a plurality of clusters that together represent a first path; and wherein the image pixels have a feed point (1003, 2003); and

[0022] (ii) non-image pixels (= Type A , Figure 17-24 ); and / or

[0023] b) a set of threshold tiles for generating a halftone image, wherein at least a portion of all halftone cells include at least 2 image clusters, where an image cluster is defined as a mutually separated group of more than 4 adjacent image pixels (= Type B , Figure 1-16 ).

[0024] The first path is preferably a space-filling curve within the halftone cell, or the first path is a spiral for generating a spiral halftone dot. The spiral halftone dot and possible variants are also disclosed in PCT / EP2018 / 079011 (AGFA NV).

[0025] In a preferred embodiment, the halftone cells of the portion have a quarter portion representing a relative image density that is at least twice the relative image density represented by the halftone cells as a whole, more preferably, the portion includes at least 10% of all halftone cells having a relative image density of less than 50%, or preferably, the portion includes at least 50% of all halftone cells having a relative image density of less than 50%. The portion may include at least 4 image clusters.

[0026] The raster image processor is preferably arranged to halftone the continuous tone image (CT) into a halftone raster image (RT) by said processor via a selected threshold tile (TT) from a threshold selector. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Six halftone cells are shown in the upper portion of the figure, each cell consisting of a 16x16 pixel grid. These halftone cells are all generated by the same threshold array using the raster image processor of the present invention. The threshold array is the matrix shown in the lower portion of the figure. Each halftone cell represents another relative image density, as indicated by the dot percentage shown below each halftone cell. Image pixels are represented by black areas in the figure, while non-image pixels are represented by white areas.

[0028] Figures 2 to 11 and Figure 1 The only difference is that another threshold array is used in each figure.

[0029] Fig.12 Six tiled halftone cells are shown, each cell comprising four groups of 3x3 image pixels.

[0030] Fig.13 and Fig.14 Shown are Figure 3 and Figure 4 The 70% halftone cells in the same 6 tiled halftone cells.

[0031] Fig.15 A halftone unit comprising 3 image clusters indicated by dashed lines AC is shown; the image pixels indicated dh do not form a group of more than 4 adjacent pixels and therefore do not meet the definition of an image cluster according to the invention.

[0032] Fig.16In the upper part of the figure, six halftone cells are shown, each consisting of a 16x16 pixel grid, and in the lower part, the threshold array used to generate these cells is shown. The thresholds in the array range from 1 to 16, which is consistent with Figure 1-11 The values ​​in the range from 1 to 256 are reversed.

[0033] Fig.17 is an enlargement of a grating image as a result of the present invention. The grating image comprises Archimedean spiral dots having a dot coverage of 50% and which are regularly tiled in a square grid.

[0034] Fig.18 is an enlargement of a grating image as a result of the present invention. The grating image comprises Archimedean spiral dots having 90% dot coverage and which are regularly tiled in a square grid.

[0035] Fig.19 Represents multiple dot coverage resulting from a thresholded tile as a result of the present invention.

[0036] Fig. 20 and Fig.21 : Fig. 20 An example of a threshold tile including thresholds from 1 to 256 is shown, which may be included in the present invention. Fig.21 Shown by Fig. 20 The spiral dots generated by the threshold patch are used for halftone dots with a threshold of 22, which corresponds to a dot coverage of 8.6% (=22 / 256).

[0037] Fig. 22 Four spiral dots are shown, including (i) image pixels arranged as a first arc (200) as an arc or as a plurality of arcs, the plurality of arcs together representing a first clockwise rotating spiral (100) as a spiral, and (ii) non-image pixels arranged as a second arc (201) as an arc or as a plurality of arcs, the plurality of arcs together representing a second clockwise rotating spiral (101) as another spiral. The first arc and the first spiral have feed points, also referred to as inner ends (2003, 1003) and outer ends (2005, 1005).

[0038] Fig.23 and Fig.24 : shows an enlargement of a raster image generated by the present invention, which raster image includes Archimedean spiral dots and additionally includes arcuate halftone dots with non-image pixels.

[0039] Fig.25 and Fig.26A raster image processor (650) of a preferred embodiment of the present invention is shown, wherein an electronic document (630) is converted into a continuous tone image (750). The raster image processor (650) includes a screen (850) for half-toning the continuous tone image (850) into a half-tone raster image (950) by selecting 1 threshold tile from N threshold tiles stored in a memory (890). The single threshold tile is selected by a threshold selector (870). The selection is based on information provided in an input field (871) regarding the substrate to be used. The half-tone raster image (950) is ready for printing by a printing device (50). Fig.26 is a raster image processor (650), wherein, additionally, the selection is based on information provided in a further input field (872) regarding the ink to be used. The printing device (50) is then able to use a plurality of inks.

[0040] The threshold selector may include an ink usage predictor, wherein a number of threshold tiles of the memory (890) are used to halftone the continuous tone image (750) into a halftone raster image whose ink usage is predicted. The one with the smallest ink usage is then selected. DETAILED DESCRIPTION

[0041] Ink Usage Predictor

[0042] The ink usage predictor is a tool for predicting the amount of ink that will be used for a halftone raster image (RT) on a selected printing device. The tool is typically a data processing system suitable for predicting said amount, or a computer program including instructions for predicting said amount. The computer program is preferably stored on a computer readable storage medium.

[0043] After halftoning a continuous tone image (CT) into a halftone raster image (RT), the pixels of the raster image are analyzed and a certain amount of ink for each pixel is determined by the ink usage predictor. The sum of the determined amounts of ink for each pixel determines the amount of ink required to print a copy of the continuous tone image on a selected substrate by a printing device. Furthermore, the amount of each ink is determined by the ink usage predictor for each non-image pixel. This does not automatically return to zero because ink can flow to the non-image pixel during or after printing until the ink is fixed on the selected substrate. Therefore, pixels from the raster image (RT) and also the neighbors of the pixels are analyzed to predict the flow of ink during or after printing until the ink is fixed on the selected substrate. For the present invention, the ink flow behavior in non-image pixels and image pixels on a selected substrate is modeled by using one or more printing targets, the printing targets comprising a plurality of patches with regularly tiled clusters, the clusters having image pixels, wherein the clusters are mixed with clusters having non-image pixels. The size and / or shape of the clusters differ between the patches.

[0044] By measuring the print density (e.g., by an XRITE 500 series spectrodensitometer) or optical density, mottle and / or ink layer thickness of a patch printed on a selected substrate, the model can be calculated for predicting the amount of ink for each pixel in a halftone raster image. For each substrate, a model can be calculated because the ink flow (e.g., by absorbance) depends on substrate parameters such as structure, composition and optical properties. For example, using an optical microscope (e.g., a scanning electron microscope (SEM)), the ink flow in non-image pixels and image pixels can be additionally determined, and the presence of ink can be measured. The amount of pigment used in the ink used for the printed patch can also be determined (e.g., by extraction) to recalculate the amount of ink used for the printed patch by knowing the percentage of pigment in the ink used. The model can use the ink amount for regularly tiled image pixels in the patch for prediction. The ink usage predictor determines from a pixel whether it has a certain similarity between the pixels of the patch, and returns a recalculation of the amount of ink for the patch, or whether the similarity matches. It is also possible to determine the amount of pigment of the used ink for a pixel in order to recalculate the amount of ink used for that pixel (printed or unprinted) by knowing the percentage of the pigment in the used ink.

[0045] The ink usage predictor may use an artificial neural network as its model, which is a computing system inspired by the biological neural networks that make up the brains of animals. More specifically, the predictor is able to train itself through the artificial neural network to determine the amount of ink required to print a halftone raster image. By using previous measurements on printed targets, printed patches and / or printed pixels, the artificial neural network is trained to complete its task on any other halftone raster image (not the printed target), regardless of the threshold tiles and continuous tone images used, namely the task of predicting the amount of ink that should be used when printing on a selected substrate.

[0046] The use of artificial neural networks is known in the technical field of the present invention, for example for color control and color management.

[0047] Raster Image Processor

[0048] A Raster Image Processor (RIP) is a tool for digitally half-toning a continuous tone image (CT) or other file formats (including PDF (Portable Document Format)) into a half-toned raster image (RT) for use in a printing device. The tool is typically a data processing system suitable for half-toning the continuous tone image (CT), or a computer program including instructions for digitally half-toning the continuous tone image (CT). The computer program is preferably stored on a computer readable storage medium. An example of such a Raster Image Processor is the Harlequin HostRenderer from Global Graphics.

[0049] A raster image processor (RIP) can convert a halftone raster image (RT) into a format that a printing device (such as an inkjet printer) can understand. In the present invention, the printing device is capable of printing on multiple substrates (S1, S2, ..., S M ) and preferably, can be printed with a variety of inks (I1, I2, ..., I Q ) printing, such as offset printing press.

[0050] Halftone raster images (RT) are mainly well-known raster graphics file formats such as TIFF TM (Tagged Image File Format), RTL (Raster Transfer Language) or BMP file formats ( Bitmap ).

[0051] Halftone raster image

[0052] In the present invention, the halftone raster image (RT) comprises regularly tiled halftone dots, which are generated by using a threshold tile (preferably a single threshold tile). The generation is done by a halftone plate, also called a halftone raster generator, which is part of a raster image processor.

[0053] The halftone raster image produced by the present invention is suitable for rendering a continuous tone image (CT), i.e., it creates the illusion of a continuous tone image (CT) on the printed copy. This requirement means that the screening frequency (i.e., the number of halftone cells arranged next to each other per length unit in the direction producing a maximum) is higher than 40 lines per inch (LPI; 15.7 lines / cm), more preferably higher than 60 LPI (23.6 lines / cm), and most preferably higher than 100 LPI (39.4 lines / cm). If the screening frequency is lower than 40 LPI, the halftone dots become visible at the viewing distance (also called reading distance), which is about 20 cm. Such low screening frequencies are typically used for artistic screening, which is used for decorative purposes, such as patterned illustrations, where it is intended that individual dots are visible to the naked eye. Therefore, halftone raster images in which the halftone dots are clearly visible at the viewing distance are not suitable for and should not be produced by the present invention.

[0054] The above mentioned screening frequency defines the spatial frequency of the halftone cells comprised in the halftone raster image. As explained above, the halftone cells in turn consist of a grid of pixels and their spatial frequency, called resolution, is expressed as dots per inch (DPI) or pixels per inch (PPI). In case the halftone raster image is written, for example on a film or a printing plate, by means of a scanning laser, the pixels are also called laser dots and the resolution then refers to the number of laser lines per inch. The halftone raster image produced in the method of the invention has a resolution of preferably greater than 600 DPI, more preferably greater than 1200 DPI. Higher resolutions of up to 9600 DPI can also be used, for example for printing security features.

[0055] Since the printing plate can only transfer single colors, it is obvious that the halftone raster image used in the method of the present invention is a black and white image, which can represent the color selection of a multi-color printing process, for example, one of the four basic colors in CMYK printing.

[0056] The quality of the printed image is preferably checked using color density measurements. The color density values ​​can then be used as input parameters for the raster image processor of the present invention. The processor, which produces a halftone raster image, adjusts the image so that the quality of the printed image is improved in subsequent print runs and / or so that more ink is saved in subsequent print runs.

[0057] Halftone Unit

[0058] The halftone raster image produced by the present invention comprises regularly tiled halftone cells. The cells may be tiled along a triangular, rectangular or hexagonal grid, and more preferably along a square grid. Fig.13 and Fig.14 Both show examples of a preferred embodiment, where 6 halftone cells are tiled into a square grid.

[0059] The halftone cells themselves also consist of a grid, more particularly of a grid of pixels, which can be image pixels or non-image pixels. These pixels preferably have the shape of regular polygons or convex polygons, for example triangles, squares, rectangles, rhombuses or hexagons. The accompanying drawings show examples of preferred embodiments, in which the halftone cells consist of a grid of square pixels.

[0060] A halftone raster image that can be generated using the RIP of the present invention by means of one of its stored threshold tiles preferably comprises halftone cells having 2 or more image clusters, i.e. mutually separated groups (= 4) of more than 4 adjacent image pixels. Type B ). In a more preferred embodiment, the halftone raster image comprises halftone cells having more than 2 image clusters, such as at least 3 or 4 image clusters, more preferably at least 5 and most preferably at least 6 image clusters.

[0061] In the above definition of "image clustering", image pixels are considered to be adjacent if they share at least one edge of the polygon. Fig.15 Three such image clusters are shown: Cluster A consists of 7 adjacent image pixels; Cluster B consists of 6 adjacent image pixels; and Cluster C consists of 5 adjacent image pixels. Image pixels d, e, and f touch another image pixel, but only through the corners of the square; since these pixels do not share edges, they are not considered adjacent, as defined above. According to the above definition, groups of 4 or fewer image pixels (such as group h) do not constitute image clusters.

[0062] Fig.12 A further refinement of the definition of image clustering used herein is illustrated.When tiling halftone cells, a group of image pixels in one halftone cell may be connected to another group of image pixels in another halftone cell with one or more adjacent edges. Fig.12 An example is shown, where a group of image pixels designated 3a is connected to a group designated 3b. According to the present invention, such groups should not be considered as separate clusters, but together represent a single cluster. Fig.12 The halftone units represented in each contain only 3 image clusters.

[0063] In contrast to conventional AM dots representing the same dot percentage, the image clusters used in the present invention allow a printed image of the same image density to be obtained with less ink. The large number of variations in the halftone dots makes it possible to optimize print quality and / or minimize ink usage. The reasons for this advantage are not fully understood, but engineers have systematically measured that a print run according to the method of the present invention consumes significantly less ink than a print run in which a printing plate is exposed using a conventional AM screen of the same original image. When compared to FM screens, it is observed that higher run lengths can be obtained because the clusters are larger than FM microdots and are therefore less susceptible to wear on the printing press. FM screens consist of multiple single image pixels or groups of four (2x2) image pixels, which are more susceptible to degradation than the image clusters used in the present invention.

[0064] Without being limited by the underlying mechanism, it is presently hypothesized that halftone cells having clustered image pixels as described above absorb thinner ink films on ink receiving areas of the plate, and / or provide better spreading of the ink film into the blank (non-image) areas between image clusters, when compared to conventional AM halftone dots representing the same relative image density. Ink saving effects have been observed for a variety of images and for a variety of printing plates. Ink savings of approximately 10% are often obtained. Ink and paper are major cost factors for printers, so even a few percentage points reduction in ink consumption represents a high cost savings. Optimization of the halftone raster image in relation to the substrate to be printed, for example by adjusting the number, size, shape and / or distribution of image clusters in the halftone cells, can result in even greater ink savings, ranging from 10% to 20% compared to conventional AM screening.

[0065] Less ink consumption provides additional advantages resulting therefrom, such as faster drying and / or less energy consumption of drying equipment, such as curing units and ovens. Faster drying is particularly advantageous for printing on uncoated plastic foils and for newspaper printing. Better spreading of the ink also reduces ink setoff, i.e. the transfer of ink from one printed copy to the back of another copy located on top of it, for example, in a printing press transport tray. Light transmission (also called print-through) is also reduced, whereby the image becomes visible on the back of a substrate, such as a thin, ink-absorbing substrate used for printing newspapers. For all these reasons, the method of the invention is particularly advantageous when carried out on a duplex printing press, i.e. a printing press that allows simultaneous printing on both sides of a substrate in one pass through the printing press.

[0066] In a preferred embodiment, the image clusters are not randomly distributed on the halftone cell, but are locally concentrated so that the image clusters together mimic conventional AM dots, and the method maintains the advantages of the AM screen as much as possible. The image clusters can be concentrated in, for example, a quarter of the halftone cell. As a result, the quarter represents a higher relative image density than the other parts of the halftone cell. More preferably, a quarter of the halftone cell has a relative image density that is at least twice the relative image density represented by the halftone cell as a whole. Figure 5 An example of such an arrangement is shown: the 8x8 pixels surrounding the center of the cell define a quarter, indicated by the bold line, which has a much higher image pixel density than the cell as a whole. The higher concentration of image pixels should not necessarily be positioned near the center of the cell: Figure 3 and Figure 4 shows different local concentrations of image pixels, yet when these cells are tiled next to each other, they represent the same halftone image, as shown in Fig.13 and Fig.14 As shown in .

[0067] The halftone raster image generated by the raster image processor from the present invention with the selected threshold tiles may contain a combination of different types of halftone cells, such as halftone cells with multiple image clusters, as defined above, combined with conventional halftone cells, such as AM halftone cells, in which all image pixels are grouped in a single cluster. One or more portions of the image may also be represented by an FM screen. In a highly preferred embodiment of the present invention, the highlights and midtones of the image, i.e., a subset of all halftone cells in the image representing a relative image density of less than 50%, consist entirely of halftone cells having 2 or more image clusters as defined above. In another embodiment, only a portion of the halftone cells representing the highlights and midtones of the image contain 2 or more image clusters. The portion may be as low as 5%. Preferably, the portion is at least 10%, more preferably at least 25% and even more preferably at least 50%.

[0068] substrate

[0069] The substrate on which the halftone grating image can be printed can be of any kind, for example, plastic film or foil, release layer, textile, metal, glass, leather, hide, cotton, and of course various paper substrates (lightweight, heavyweight, coated, uncoated, paperboard, cardboard, etc.). The substrate can be a rigid workpiece or a flexible sheet, roll or sleeve. Preferred flexible materials include, for example, paper, transparent foil, adhesive PVC sheet, etc., which can be less than 100 microns thick, and preferably less than 50 microns thick. Preferred rigid substrates include, for example, hardboard, PVC, carton, wood or ink receiver, which can be up to 2 cm thick, and more preferably up to 5 cm thick. The substrate can also be a flexible mesh material (e.g., paper, adhesive vinyl, fabric, PVC, textile). A receiving layer (e.g., an ink receiving layer) can be applied to the substrate to adhere the reproduced image well to the substrate.

[0070] The printing quality on the substrate depends on several factors. With the selected threshold tiles from the present invention, the printing quality becomes better. The several factors are, for example:

[0071] - the amount of paper sizing additive in the substrate;

[0072] - Smoothness, mass density and caliper variation of substrate;

[0073] -Strength and dimensional stability of the substrate;

[0074] - porosity of the substrate;

[0075] -Moisture and curling of the substrate.

[0076] However, there are also some factors that affect the printing quality of paper optics and appearance, such as brightness, whiteness, opacity, and specular gloss.

[0077] Threshold Tile

[0078] According to the invention, a halftone raster image is generated by thresholding tiles, preferably a single thresholding tile. Digital halftoning by means of thresholding tiles (sometimes also referred to as thresholding matrices or thresholding arrays) is known in the art. When used for multi-color printing, the number of thresholding tiles is preferably the same as the number of color channels in the original continuous tone image.

[0079] Digital halftoning using a threshold tile generally means that the original image is sampled into cells that map onto the threshold tile. The local density value of the original image is then compared to each value in the array (if necessary, the density range of the original image is adjusted so that it equals the range in the array). If the original density value is below the threshold for that pixel, the output pixel is set to 0 (=OFF). Otherwise, if the density value equals or exceeds the threshold, the output pixel is set to 1 (=ON). These steps are repeated for all cells in the image.

[0080] The size of the array (ie the number of pixels per halftone cell) may depend on various factors such as the resolution of the image setter and the desired quality of the printed image. The array is preferably arranged as a square (nxn size) or a rectangle (mxn, where m>n). Figure 1-16 Examples of square threshold tiles of size 16x16 positions are shown, where each position contains a threshold value within a specific range. In these specific examples, the threshold range (1-256) is equal to the number of positions in the array (16x16); in other embodiments, such as the example shown in Figure CL16, the value range may be lower than the number of positions, and then each individual value may appear at multiple positions in the array.

[0081] To produce a higher relative image density, the threshold tiles are designed in such a way that the number and / or size of the image clusters increases in line with the corresponding density of the original image. Figure 1 A cell representing a relative image density of 25% with 7 image clusters is shown, the size of the image clusters growing with increasing image density. Figure 3 A 10% cell with 5 image clusters is shown, where both the size and number of clusters grow at higher image densities. While the image density of the halftone cell grows by adding image pixels, it is preferred to keep the non-image pixels together in non-image clusters, which are defined as mutually separated groups of adjacent non-image pixels. By keeping the number of non-image clusters in the shadows of the image as low as possible, the ink can be spread to a higher extent than if the non-image pixels were isolated or distributed over multiple clusters. In this way, the ink can also be preserved in the shadow areas of the image.

[0082] In a preferred embodiment using spiral halftone dots, the relative image density can be increased by increasing the length and / or thickness of the first spiral (which comprises the image pixel), e.g. Figure 6or by inserting image pixels inside the second spiral; or by any combination of these methods. In the shadows of the image, more image pixels are added to the halftone cells in such a way that the ink channel formed by the second spiral (which includes the non-image pixels) shrinks and / or becomes thinner, as shown in FIG. Figure 6 and Fig. 9 As shown in .

[0083] In a preferred embodiment, a plurality of threshold tiles (TT1, TT2, ..., TT N )yes

[0084] a) A thresholding block for generating a halftone image, wherein at least a portion of all halftone cells are halftone dots comprising:

[0085] (i) image pixels arranged as a first cluster or a plurality of clusters that together represent a first path; and wherein the image pixels have a feed point (1003, 2003); and

[0086] (ii) non-image pixels (= Type A, Figure 17-24 ); and / or

[0087] b) a thresholding block for generating a halftone image, wherein at least a portion of all halftone cells comprises at least 2 image clusters, an image cluster being defined as mutually separated groups (= Type B , Figure 1-16 ). Preferred embodiments and advantages of Type B are described under the heading "Halftone Unit".

[0088] For both types (Type A and Type B), many variations can be generated, but it was found that they had to be fine-tuned depending on the chosen substrate and / or the chosen ink. Both types have similar advantages, such as producing a thinner ink layer on the chosen substrate.

[0089] The substrate is also a substrate type in the present invention. The ink is also an ink type in the present invention.

[0090] For multiple clusters with a first path represented together Type A The first path may be part of a space-filling curve (such as a Hilbert curve or a Peano curve) in the halftone unit.

[0091] All clusters that together make up the first path are preferably interconnected so that the first path represents a continuous line following the path. The first path may also contain isolated non-image pixels, or may include discontinuous clusters, such that the first path is interrupted by empty spaces at one or more locations. In this embodiment, the empty spaces separating adjacent clusters of the first path may be considered as protrusions of the second path into the first path. Such protrusions of the second path may completely cut the first path into discontinuous clusters, or incompletely, so that the first path is not interrupted but is locally reduced to a lower thickness.

[0092] In a preferred embodiment, the first cluster is an arc (200) and / or the first plurality of clusters is a plurality of arcs, which together represent a first spiral (100) as a first path. Accordingly, the second cluster is another arc (201) and / or the second plurality of arcs is a plurality of arcs, which together represent a second spiral (101) as a second path (preferably along said first path). Such dots will be referred to herein as "spiral halftone dots". Image pixels are represented by the black areas in the figure. Non-image pixels define non-printing areas and correspond to the empty spaces left in the dots as represented by the white areas in the figure. Fig. 22 The two dots on the left hand side have low dot coverage (a low percentage of the image pixels) and represent the strong lights in the image, while Fig. 22 The two dots on the right hand side have high dot coverage and represent the shadows of the image. A first spiral as the first path is a preferred embodiment, but a cross path as the first or second path is also part of the invention. The first and second paths may also not be spirals.

[0093] The first path (preferably a spiral) grows in length from the feed point (2003, 1003) (also referred to as the inner end) along the path (preferably the spiral direction) to the outer end (2005, 1005). Typically from mid-tone to shadow, the path (preferably a spiral) may overlap with adjacent halftone dots ( Fig.19 ). If the first path is a spiral, the growth is also defined by the starting angle of its bend or winding. This is different from AM halftone dots which expand a single cluster into a larger single cluster.

[0094] In the highlights of the image, the number of image pixels per dot is low, so that they cannot form a complete winding of the first spiral, but only a portion thereof, which is referred to as the "first arc". The empty space partially surrounded by the first arc can also be considered as another arc, which is referred to herein as the "second arc". In the mid-tones and shadows of the image, the number of image pixels per dot is high, so that they can form one or more windings of the "first spiral", thereby also defining a "second spiral" of non-image pixels defined by the empty spaces between the windings of the first spiral (see, e.g. Fig.19 ).

[0095] Without being bound by theory, it can be observed when magnifying the printed image that the shape and size of the printed ink blob is less affected by uncontrolled diffusion of the ink because when the ink blob is pressed onto the substrate, such as by a printer, excess ink printed by a first cluster or first path can flow into the empty space corresponding to the second cluster or second path. However, the diffusion is substrate and / or ink dependent. The empty space defines an ink channel that can receive ink printed from the first cluster / path, thereby providing a means for controlling the diffusion of the ink.

[0096] For type B, multiple image clusters within a halftone unit are preferably grouped together within a virtual circle or virtual ellipse or virtual ellipse. Figure 2 and Figure 3 , where image clusters are positioned within a virtual circle that preferably grows depending on the local density value of a continuous image such as in an AM halftone dot.

[0097] Threshold Selector

[0098] A threshold selector is a tool for selecting a threshold tile based on one or more conditions. The tool is typically a data processing system adapted to select a threshold from a plurality of thresholds, or a computer program comprising instructions for selecting the threshold. The computer program is preferably stored on a computer readable storage medium.

[0099] In the present invention, the plurality of threshold blocks (TT1, TT2, ..., TT N ) are stored in a memory, and one or more conditions are based on information provided to an input field regarding the substrate to be used. The number of threshold tiles is preferably greater than 5, more preferably greater than 10.

[0100] The input fields from the present invention are preferably part of a graphical user interface (GUI) shown on a computer display such as disclosed in US9058105B2 (International Business Machines Corporation). The input fields are preferably GUI features such as list boxes, combo boxes and / or editable text fields that give the RIP user a variety of ways to enter or select desired information. The input fields can be part of a dialog box from the RIP.

[0101] Prepress Workflow System

[0102] A prepress workflow system is a tool for managing digital documents, preferably in a page description language (PDL) such as Postscript. TM) is defined as a prepress workflow system, wherein the document is prepared for printing on a printing device, such as an offset printing press. The tool is typically a data processing system suitable for managing and preparing the document for printing, or a computer program including instructions for managing and preparing the document for printing. The computer program is preferably stored on a computer readable storage medium. An example of such a prepress workflow system is Apogee from AGFANV. TM .

[0103] In a preferred embodiment, a prepress workflow system comprises a raster image processor from the present invention and further comprises means for transferring a halftone raster image (RT) to a digital printing press or plate setter to obtain a printing plate. The printing plate is preferably a lithographic printing plate or a flexographic printing plate.

[0104] Printing Plate

[0105] The printing plate of the invention is obtained by exposing a halftone raster image on a photosensitive or thermosensitive material called a printing plate precursor. The plate precursor can be positive or negative. The positive plate precursor has a coating which, after exposure and development, accepts ink in non-exposed areas and does not accept ink in exposed areas. The negative plate accepts ink in exposed areas and does not accept ink in non-exposed areas. The image pixels shown in the figures define the ink-receiving areas of the plate and therefore correspond to the exposed or unexposed areas of the negative or positive plate precursor, respectively.

[0106] The plate of the present invention is preferably a lithographic printing plate or a flexographic printing plate. The lithographic printing plate is usually obtained by exposing a halftone grating image to a photosensitive or thermosensitive coating of a printing plate precursor by means of a scanning laser, preferably a violet or near-infrared laser, or another digitally modulated light source (such as a digital mirror device, LCD or LED display). After treating the exposed precursor with a suitable developer, a lithographic printing plate with a halftone grating image of the present invention is obtained. The plate can then be mounted on a lithographic printing press, preferably an offset printing press, wherein ink is provided to the plate and then transferred to the substrate to be printed. Alternatively, the exposed precursor can be mounted directly on the printing press, i.e., without any prior liquid treatment or other development, and then the development of the image can occur with the aid of ink and / or ink fountain provided to the plate at the beginning of printing.

[0107] Flexographic printing plates are usually obtained by UV exposure of a photopolymer coating, usually using a UV lamp through a mask, which can be a graphic film in contact with the photopolymer coating or an in-situ mask present on top of the photopolymer coating. The mask is preferably obtained by exposing a halftone raster image on a film or on an in-situ mask layer by means of a scanning laser, preferably a near infrared layer.

[0108] Data processing system

[0109] The data processing system runs one or more computer programs, for example, a raster image processor. The present invention includes such a data processing system capable of carrying out the halftoning method of the present invention and its preferred embodiments.

[0110] Part or all of the data processing system and / or its functional units or blocks may be implemented in one or more circuits or circuit systems, such as (one or more) integrated circuits or as LSI (large scale integration). Each functional unit or block of the data processing system may be made into an integrated circuit chip separately. Alternatively, part or all of the functional units or blocks may be integrated and made into an integrated circuit chip.

[0111] A software program, also referred to as a computer program, runs in a data processing system and is a program that controls a processor to implement the functions of various preferred embodiments of the present invention. Therefore, the information processed by the data processing system is temporarily accumulated in the RAM during processing. Thereafter, the information can be stored in various types of circuits in the form of ROM and HDD, and read out by a circuit system included in or in combination with the data processing system as required, and modified or written to it. As a recording medium for storing programs, any one of semiconductor media (e.g., ROM, non-volatile memory card, etc.), optical recording media (e.g., DVD, MO, MD, CD, BD, etc.) and magnetic recording media (e.g., magnetic tape, floppy disk, etc.) can be used. In addition, by executing the loaded software program, not only the functions of various preferred embodiments of the present invention are implemented, but also the functions of the preferred embodiments of the present invention can be implemented by processing the loaded software program in combination with an operating system or other application programs based on the instructions of the program.

[0112] Furthermore, in the case of a distributed prepress workflow system or even a distributed raster image processor, the program can be distributed by being stored in a portable recording medium, or the program can be transmitted to a server computer connected via a network (such as the Internet). In addition, a part of a terminal device, a wireless base station, a host system or other device, or all of it can be implemented as an LSI, which is generally an integrated circuit. Each functional unit or block of the data processing system can be individually chip-ized, or a part of it or its entirety can be chip-ized by being integrated. In the case of making each functional block or unit into an integrated circuit, an integrated circuit controller that controls the integrated circuit is added.

[0113] Finally, it should be noted that descriptions referring to "circuit" or "circuit system" are by no means limited to hardware implementations only, and as a person skilled in the relevant art will know and understand, such descriptions and narratives of "circuit" or "circuit system" include combined hardware and software implementations, where the circuit or circuit system is operable to perform functions and operations based on any form of machine-readable program, software or other instructions that can be used to operate the circuit or circuit system.

[0114] There is no limitation on the location of the data processing system (18), it may be located at a prepress office, at a printing facility, or even at a third party location.

[0115] The digital connection to the data processing system can be made in any form. It can be a connection using optical fiber or a wireless connection, such as a wifi connection according to the IEEE 802.11 standard.

Claims

1. A raster image processor (RIP) for digitally binary half-toning a continuous tone image (CT) into a half-tone raster image (RT) by means of a single threshold tile (TT) for enabling the use of multiple substrates (S1, S2, ..., S M ) in, The processor comprises: - Input fields with information about the substrate to be used; - a memory on which a plurality of threshold value tiles (TT1, TT2, ..., TT2) for generating regularly tiled halftone dots are stored N ), wherein the plurality of threshold tiles are used to halftone the continuous tone image (CT) into a plurality of halftone raster images; an ink usage predictor configured to predict a plurality of ink amounts to be used for a plurality of halftone raster images to be printed on the substrate to be used, wherein the predicted plurality of ink amounts are obtained by using the plurality of threshold tiles (TT1, TT2, ..., TT N ) is calculated from a plurality of halftone raster images of said continuous tone image (CT); and a threshold selector capable of selecting said plurality of threshold tiles (TT1, TT2, ..., TT3) based on information about the substrate provided to an input field and additionally based on a predicted amount of ink from said ink usage predictor N ) in the single threshold tile (TT).

2. The processor (RIP) according to claim 1, in, Printing equipment can use a variety of inks (I1, I2, ..., I Q ) for printing, and wherein the processor further includes another input field containing information regarding the ink to be used; and Therein, the threshold selector can additionally determine a single threshold tile (TT) based on information about the ink provided to another input field.

3. The processor (RIP) according to claim 2, wherein: Regularly tiled halftone dots are arranged according to a screening frequency greater than 100 lines per inch.

4. The processor (RIP) according to claim 3, wherein: Regularly tiled halftone dots are arranged according to a screen angle selected from the group consisting of 0°, 7.5°, 15°, 22.5°, 75°, 45°, 67.5°, and 82.5°.

5. The processor (RIP) according to claim 4, wherein: Multiple threshold tiles (TT1, TT2, ..., TT N ) comprises a set of threshold tiles for generating a halftone image, wherein at least a portion of all halftone cells are halftone dots comprising: (i) image pixels arranged as a first cluster or a plurality of clusters that together represent a first path; and wherein the image pixels have a feed point (1003, 2003); and (ii) Non-image pixels arranged into a second cluster or clusters that together represent a second path.

6. The processor (RIP) according to claim 5, wherein: The first path is a space-filling curve inside the halftone cell.

7. The processor (RIP) according to claim 5, wherein: The first path is a spiral.

8. The processor (RIP) according to claim 4, wherein: Multiple threshold tiles (TT1, TT2, ..., TT N ) comprises a set of threshold tiles for generating a halftone image, wherein at least a portion of all halftone cells comprise at least 2 image clusters, an image cluster being defined as mutually separated groups of more than 4 adjacent image pixels.

9. The processor (RIP) according to claim 8, wherein: The portion of the halftone cell has a quarter portion representing a relative image density that is at least twice the relative image density represented by the halftone cell as a whole.

10. The processor (RIP) according to claim 8, wherein: The portion comprises at least 10% of all halftone cells having a relative image density of less than 50%.

11. The processor (RIP) according to claim 8, wherein: The portion includes at least 4 image clusters.

12. A prepress workflow system comprising a raster image processor according to any one of the preceding claims, wherein: The prepress workflow system further comprises: - Means for transferring a halftone raster image (RT) to a digital printing press or plate-setter for obtaining a printing plate.

13. The prepress workflow system according to claim 12, wherein: The printing plate is either a lithographic plate or a flexographic plate.

Images