Hp Indigo B.v.

Hewlett-packard Indigo B.v.

Hewlett-packard Development Company, L.p.

Purdue Research Foundation

Tal Frank

Oren Haik

Ram Dagan

Yotam Ben-Shoshan

Dror Kella

Marina Limonov

Boaz Tagansky

Oded Perry

Tamar Kashti

Robert Alan Ulichney

Jan Philip Allebach

Guy Nesher

Ran Waidman

Noam Shaham

Gregory Braverman

Haim Vladomirski

Oron Ambar

Nir Guttman

Yuval Yunger

Liron Itan

Mirta Perlman

Craig Breen

Shay Bornstein

Altyngul Jumabayeva

Liron Iton

In an example, a method includes determining, using a processor, a first halftone screen comprising a plurality of cells. Each of the cells may contain a predetermined pixel cluster pattern, and a centre position of a cluster pattern within a first cell may be different to a centre position of a cluster pattern within a second cell.

Halftone screens comprising cluster patterns having different centre positions

In an example, a method includes determining an indication of pixel separation for an image region to be printed to a substrate. A power level of a laser light source to address a pixel on a region of a photoconductive surface corresponding to the image region may be adjusted based on the indication of pixel separation to compensate for print spot size variation associated with pixel separation.

Adjusting power levels to compensate for print spot size variation

Examples analyze a digital image to determine an amount of high-frequencies corresponding to each pixel of the digital image based at least in part on gradients corresponding to a pixel neighborhood of each pixel. Examples analyze the digital image to determine a degree of randomness for each pixel based at least in part on the corresponding gradients. Examples generate an activity mask for the digital image based at least in part on the amount of high-frequencies and the degree of randomness corresponding to each pixel. Examples process the pixels of the digital image by performing gray component replacement to generate a color transformed image based at least in part on the activity mask.

Gray component replacement in a digital image to generate a color transformed image

Measures for use in calibrating a printing device. Historical dot gain linearization lookup table data for the printing device is processed. On the basis of the processed historical dot gain linearization lookup table data, a plurality of input points for a current dot gain linearization lookup table are dynamically determined. The printing device is calibrated according to the dynamically determined current dot gain linearization lookup table.

Dynamic dot gain lookup table generation

An example system includes a color engine to separate an image into a plurality of color components. The system also includes a halftone engine to generate a plurality of halftone images based on the plurality of color components and a plurality of halftone screens. For each halftone screen, the halftone cell centers for that halftone screen occur at regular or semi-regular distances relative to a dot pitch. The plurality of halftone screens forms a high frequency moire pattern when the halftone screens are overlaid on each other. Each of the halftone screens have a granularity metric less than a threshold.

Halftone screens

Certain examples described herein relate to the halftoning of a color image. In one example, a set of clusters are determined based on the color image. A set of edges are also detected in the color images. Clusters within these edges are then merged. A set of screens for halftoning are assigned to the set of clusters. This assignment is based on color property metrics for the set of clusters. The color image is halftoned using the set of screens assigned to the merged clusters.

Assigning halftone screens to clustered image portions based on color and content

A halftone comprises a first halftone screen and a second halftone screen. The first halftone screen comprises a first plurality of amplitude modulated dots arranged according to a first plurality of rows, the first plurality of rows being orientated according to a first direction and comprising a first dot spacing. The second halftone screen comprises a second plurality of amplitude modulated dots arranged according to a second plurality of rows, the second plurality of row being orientated in a second direction and comprising a second dot spacing. The first direction and the second direction define an angle of 45 degrees or less and a ratio of the second dot spacing to the first dot spacing is less than one.

Generating halftones

A method of determining the velocity of relative displacement between a substrate and an image sensor, for example the velocity of displacement of a page relative to a scanner, involves imaging a reference pattern on the substrate, using the image sensor, while the relative displacement occurs between the substrate and the image sensor. The reference pattern includes plural crossing points marked at predetermined locations on the substrate, each crossing point formed of a first line portion crossing a second line portion. Locations in the image that correspond to the crossing points are compared to the predetermined locations on the substrate and the velocity of the relative displacement between the image sensor and the substrate is determined using relationships between the predetermined locations and the detected locations in the generated image.

Velocity estimation methods, and imaging devices and printing devices using the methods

A system includes a structure module, graininess module, mottle module, and standard deviation (STD) module. The structure module is to identify a structure metric based on an input digital image, and remove a structured nonuniformity from the input digital image to produce a second input digital image. The graininess module is to identify a graininess metric based on the second input digital image. The mottle module is to identify a mottle metric based on the second input digital image. The STD module is to identify a STD metric that is to correspond to overall smoothness of the input digital image.

Metrics to identify image smoothness

A halftone screen may be used to transform a continuous tone image into a halftone image. Determining the halftone screen may include determining a first halftone tile for a first gray level, selecting pixel locations and increasing the intensity of pixels at the locations to activate the pixels to form a second halftone tile for a subsequent gray level. A filtered image may be generated from the second halftone tile, and pixels from the filtered image may be used to generate the halftone screen.

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Tal Frank