Abstract: Apparatus to detect a defect in a printed image and methods of detecting detects in a printed image are described. In some examples, a printing operation is initiated using image data to generate a printed image. The printed image is then scanned to generate a scanned image. A resolution of the scanned image is estimated, calculated or determined on the basis of a characteristic of the printing operation, and a reference image, having a resolution corresponding to the estimated, calculated or determined resolution, is generated from the image data. Whether defects are present in the printed image may be determined on the basis of a comparison of the reference image with the scanned image.

Abstract: 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.

Abstract: Streaks in images are detected by determining a rotation angle of an image and calculating a rotated image based on a rotation of the image by the rotation angle. A cross-sectional pixel profile of the rotated image is determined and a peak in the cross-sectional pixel profile of the rotated image is determined. A streak in the image is identified based on the determined peak.

Abstract: A method of detecting Moire artefacts in a digital image comprises calculating at least one parameter relating to at least one feature of the digital image. The at least one parameter is compared to at least one corresponding threshold, wherein the at least one threshold is determined by a machine learning process, based on a set of example images and reference parameters for the set of example images. It is determined whether the digital image contains Moire artefacts based on the results of the comparing.

Abstract: A method includes obtaining an image of a document against a background. A bounding box that bounds a region of the image that is distinguishable from the background is found. Coordinates of a plurality of points of the distinguishable region are found, each point being a point of the distinguishable region that is closest to each corner of the bounding box. The document is identified within the image as a region of the image whose corners are defined by the found coordinates.

Abstract: Printing with a single colorant a security feature imperceptible to the naked eye. For a digital security image having a first region formed by a first pattern of binary pixels and a second region formed by a different second pattern of binary pixels, the first and second patterns are printed with the single colorant. A darker one of the first and second printed patterns is determined. The security image is printed with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.

Abstract: Printing with a single colorant a security feature imperceptible to the naked eye. For a digital security image having a first region formed by a first pattern of binary pixels and a second region formed by a different second pattern of binary pixels, the first and second patterns are printed with the single colorant. A darker one of the first and second printed patterns is determined. The security image is printed with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.

Abstract: Printing with a single colorant a security feature imperceptible to the naked eye. For a digital security image having a first region formed by a first pattern of binary pixels and a second region formed by a different second pattern of binary pixels, the first and second patterns are printed with the single colorant. A darker one of the first and second printed patterns is determined. The security image is printed with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.

Abstract: 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.

Abstract: 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.

Abstract: A method to generate an image in which a plurality of offset vectors for portions of a first image are determined by comparing the similarity of the portions to portion of a second image.

Abstract: A method to generate a histogram matched image in which a portion of a first reference image is partitioned into a plurality of regions. Histogram matching is performed separately on the plurality of regions of the first reference image and corresponding regions in a second image to generate a plurality of first histogram matched reference images. Histogram matching is also performed on the portion of the first reference image and a corresponding portion in the second image to generate a second histogram matched reference image. An area from one of at least a first histogram matched reference image and the second histogram matched reference image is selected to generate a finalized histogram matched reference image.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A method to generate an image in which a plurality of offset vectors for portions of a first image are determined by comparing the similarity of the portions to portion of a second image.

Abstract: A method to generate a histogram matched image in which a portion of a first reference image is partitioned into a plurality of regions. Histogram matching is performed separately on the plurality of regions of the first reference image and corresponding regions in a second image to generate a plurality of first histogram matched reference images. Histogram matching is also performed on the portion of the first reference image and a corresponding portion in the second image to generate a second histogram matched reference image. An area from one of at least a first histogram matched reference image and the second histogram matched reference image is selected to generate a finalized histogram matched reference image.

Abstract: Printing with a single colorant a security feature imperceptible to the naked eye. For a digital security image having a first region formed by a first pattern of binary pixels and a second region formed by a different second pattern of binary pixels, the first and second patterns are printed with the single colorant. A darker one of the first and second printed patterns is determined. The security image is printed with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.

Abstract: A method includes obtaining an image of a document against a background. A bounding box that bounds a region of the image that is distinguishable from the background is found. Coordinates of a plurality of points of the distinguishable region are found, each point being a point of the distinguishable region that is closest to each corner of the bounding box. The document is identified within the image as a region of the image whose corners are defined by the found coordinates.

Abstract: A set of screens is provided for use in printing respective color separations in a halftone color printing process. This set of screens comprises at least two clustered-dot screens and the frequency and angle parameter values of the screens is such that the lowest frequency moiré produced by any combination of at least two frequency components, taken from the group comprising the first and second screen harmonics, for which the sum of the harmonic orders of the frequency components in the combination is less than a predetermined value, is of a sufficiently high frequency as to be substantially unperceivable to the human visual system; other moirés are also substantially unperceivable to the human visual system. The lowest frequency moiré serves to reduce the visibility of color changes caused by color plane registration variations. A printing system and method employing the screen set are also provided.