Abstract: A light source adjustment apparatus is disclosed. The light source adjustment apparatus includes processing apparatus to receive a scanned image of a pattern printed by a print apparatus onto a printable medium, the pattern including a plurality of blocks of print agent of a first colour printed during a printing operation in which light sources of a light source array irradiate a photoconductive surface; analyse the scanned image to identify a region of non-uniformity within the plurality of blocks of print agent; correlate a location of the identified region of non-uniformity with a corresponding light source in the light source array; determine, based on the identified region of non-uniformity, an adjustment to be made to a parameter of the corresponding light source; and generate a signal to effect the determined parameter adjustment with regard to the corresponding light source. A method and a print apparatus are also disclosed.

Abstract: A focus adjustment method is disclosed. The focus adjustment method includes depositing, using a print apparatus, print agent onto a printable substrate, the print apparatus comprising a photoconductive surface and a writing head having a first end and a second end, the writing head having an array of light sources to emit radiation onto the photoconductive surface during a printing operation. The method also includes during said depositing, moving the writing head relative to the photoconductive surface, between a first position and a second position, to create a printed image. The method also includes determining, based on the printed image, for each of a plurality of locations along the writing head, a position of the writing head relative to the photoconductive surface at which the writing head is most focussed.

Abstract: Certain examples described herein relate to a method of electro-photographic printing. In an example a calibration image having one or more gray levels is printed using an optical element. The contrast of the printed calibration image is increased when the calibration image has a gray coverage below a threshold. The printed calibration image is scanned to determine adjustment factors for the optical element for the one or more gray levels. The adjustment factors are applied to the optical element when printing a non-calibration image.

Abstract: In an example, a method includes determining a first scaling to be applied to a first print operation and a second scaling to be applied to a second print operation. Each print operation includes selectively removing charge from a charged photoconductor by irradiating the photoconductor in a plurality of scans, forming a first print agent pattern on the photoconductor and delivering the first print agent pattern to a substrate. If the first and second scalings are different, a control instruction may be determined to change the scan-to-scan spacing between the first and second print operations.

Abstract: A light source adjustment apparatus is disclosed. The light source adjustment apparatus includes processing apparatus to receive a scanned image of a pattern printed by a print apparatus onto a printable medium, the pattern including a plurality of blocks of print agent of a first colour printed during a printing operation in which light sources of a light source array irradiate a photoconductive surface; analyse the scanned image to identify a region of non-uniformity within the plurality of blocks of print agent; correlate a location of the identified region of non-uniformity with a corresponding light source in the light source array; determine, based on the identified region of non-uniformity, an adjustment to be made to a parameter of the corresponding light source; and generate a signal to effect the determined parameter adjustment with regard to the corresponding light source. A method and a print apparatus are also disclosed.

Abstract: A focus adjustment method is disclosed. The focus adjustment method includes depositing, using a print apparatus, print agent onto a printable substrate, the print apparatus comprising a photoconductive surface and a writing head having a first end and a second end, the writing head having an array of light sources to emit radiation onto the photoconductive surface during a printing operation. The method also includes during said depositing, moving the writing head relative to the photoconductive surface, between a first position and a second position, to create a printed image. The method also includes determining, based on the printed image, for each of a plurality of locations along the writing head, a position of the writing head relative to the photoconductive surface at which the writing head is most focussed.

Abstract: 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.

Abstract: In an example, a method includes determining a first scaling to be applied to a first print operation and a second scaling to be applied to a second print operation. Each print operation includes selectively removing charge from a charged photoconductor by irradiating the photoconductor in a plurality of scans, forming a first print agent pattern on the photoconductor and delivering the first print agent pattern to a substrate. If the first and second scalings are different, a control instruction may be determined to change the scan-to-scan spacing between the first and second print operations.

Abstract: In one example, a calibration of a print engine may include producing an image by scanning imaging elements along a scan direction, the image having a calibration portion that is continuous or unbroken in a direction perpendicular to the scan direction. Information indicative of an optical measurement of the calibration portion is received. A contribution to the optical measurement associated with each of the laser elements in the group of laser elements is determined. A calibration adjustment for the laser elements in the group of laser elements is determined.

Abstract: 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.

Abstract: Certain examples described herein relate to an optical controller (140) for an exposure unit (115, 215) of a printer. In certain examples, memory (150) stores a plurality of data structures each comprising adjustment factors useable to adjust a plurality of optical elements (216) of the exposure unit. Different data structures correspond to different gray coverages in an image generated by the printer. In certain examples, a processor (160) determines gray levels for different image regions in input image data. In certain cases, the processor links the determined gray levels to corresponding data structures within the plurality of data structures to obtain adjustment factors for the different image regions. In certain cases, the processor adjusts the optical elements for each image region using the corresponding obtained adjustment factors to enable the generation of an exposed image using the exposure unit based on the input image data.

Abstract: Certain examples described herein relate to an optical controller (140) for an exposure unit (115, 215) of a printer. In certain examples, memory (150) stores a plurality of data structures each comprising adjustment factors useable to adjust a plurality of optical elements (216) of the exposure unit. Different data structures correspond to different gray coverages in an image generated by the printer. In certain examples, a processor (160) determines gray levels for different image regions in input image data. In certain cases, the processor links the determined gray levels to corresponding data structures within the plurality of data structures to obtain adjustment factors for the different image regions. In certain cases, the processor adjusts the optical elements for each image region using the corresponding obtained adjustment factors to enable the generation of an exposed image using the exposure unit based on the input image data.

Abstract: An electric cross-talk, ECT, effect of laser-diode array is measured by capturing a first image of a first laser spot of a first laser diode with a second laser diode being turned off (10) and a second image of a second laser spot of the first laser diode while switching on the second laser diode (20). A spot-energy ratio is determined (30) by processing the images, and an ECT-coupling coefficient on the first laser diode is calculated (40) by switching the second laser diode. Compensating for the ECT effect includes determining a signal for predicting the ECT effect on the first laser diode by switching the second laser diode, and generating a driving signal based on a desired current profile and the ECT-prediction signal.

Abstract: A method of controlling a print engine, the method comprising: printing a first test image including a number of scans of printing components at a first setting of the array of printing components; printing at least a second test image by a number of scans of the printing components at a modified setting of the array of printing components, the modified setting being different from the first setting, wherein the modified setting provides a modified setting for each one of the printing components which is varied according to the position of the respective printing component in the array; optically scanning the printed test images and determining the distinctiveness of a scan band within the printed test images for each one of the test images; and deriving an optimum setting of the array of printing components from a comparison of the determined distinctiveness.

Abstract: In one example, an imaging system (10) for a laser printer includes: an imaging laser (26) in which, within a range of drive currents, a threshold current of the laser varies with temperature and an efficiency of the laser does not vary with temperature; a power sensor (20) to measure an output power of the laser at a drive current within the range of drive currents; and a temperature control device (32) to change the temperature of the laser based on an output power measured by the power sensor.

Abstract: An electric cross-talk, ECT, effect of laser-diode array is measured by capturing a first image of a first laser spot of a first laser diode with a second laser diode being turned off (10) and a second image of a second laser spot of the first laser diode while switching on the second laser diode (20). A spot-energy ratio is determined (30) by processing the images, and an ECT-coupling coefficient on the first laser diode is calculated (40) by switching the second laser diode. Compensating for the ECT effect includes determining a signal for predicting the ECT effect on the first laser diode by switching the second laser diode, and generating a driving signal based on a desired current profile and the ECT-prediction signal.

Abstract: A method of controlling a print engine, the method comprising: printing a first test image including a number of scans of printing components at a first setting of the array of printing components; printing at least a second test image by a number of scans of the printing components at a modified setting of the array of printing components, the modified setting being different from the first setting, wherein the modified setting provides a modified setting for each one of the printing components which is varied according to the position of the respective printing component in the array; optically scanning the printed test images and determining the distinctiveness of a scan band within the printed test images for each one of the test images; and deriving an optimum setting of the array of printing components from a comparison of the determined distinctiveness.

Abstract: A method and apparatus are provided for evaluating the severity in a printed image of a repeating band print artifact. After electronically capturing the printed image, each of a plurality of patches taken from captured image is analysed to produce an artifact severity measure for the patch; an overall artifact severity value is then determined for the printed image from the patch severity measures. The analysis of each patch involves producing a spatial intensity profile across the patch substantially at right angles to an expected direction of extent of any repeating band print artifact present; a Fourier-related transform is then applied to the spatial intensity profile and the patch artifact severity measure generated by summing the resultant spatial frequency coefficients in a limited range about a frequency of interest.

Abstract: An optical beam is selectively output towards a scanner in accordance with image data for a scan line of an image. The optical beam has a beam irradiance distribution that is elliptical in shape. The optical beam passes through an aperture stop, ordinarily creating side lobes within a focus irradiance distribution of the optical beam. The scanner scans the optical beam to form the scan line on a photosensitive surface by selectively exposing positions along the scan line in accordance with image data. The optical beam is modified before it reaches the photosensitive surface to substantially remove the side lobes that have been created within the focus irradiance distribution and/or to substantially prevent the side lobes from being created within the focus irradiance distribution of the optical beam.

Abstract: A method and apparatus are provided for evaluating the severity in a printed image of a repeating band print artifact. After electronically capturing the printed image, each of a plurality of patches taken from captured image is analysed to produce an artifact severity measure for the patch; an overall artifact severity value is then determined for the printed image from the patch severity measures. The analysis of each patch involves producing a spatial intensity profile across the patch substantially at right angles to an expected direction of extent of any repeating band print artifact present; a Fourier-related transform is then applied to the spatial intensity profile and the patch artifact severity measure generated by summing the resultant spatial frequency coefficients in a limited range about a frequency of interest.