WO2023075788A1 - Étalonnage d'imprimante - Google Patents

Étalonnage d'imprimante Download PDF

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Publication number
WO2023075788A1
WO2023075788A1 PCT/US2021/057306 US2021057306W WO2023075788A1 WO 2023075788 A1 WO2023075788 A1 WO 2023075788A1 US 2021057306 W US2021057306 W US 2021057306W WO 2023075788 A1 WO2023075788 A1 WO 2023075788A1
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WO
WIPO (PCT)
Prior art keywords
area
printed
levels
color rendering
optical power
Prior art date
Application number
PCT/US2021/057306
Other languages
English (en)
Inventor
Tsafrir YEDID AM
Pavel BLINCHUK
Uri Lidai
Original Assignee
Hewlett-Packard Development Company, L.P.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hewlett-Packard Development Company, L.P. filed Critical Hewlett-Packard Development Company, L.P.
Priority to PCT/US2021/057306 priority Critical patent/WO2023075788A1/fr
Publication of WO2023075788A1 publication Critical patent/WO2023075788A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46—Colour picture communication systems
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control
    • H04N1/603—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer
    • H04N1/6033—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer using test pattern analysis
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
    • G03G15/043—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for controlling illumination or exposure
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/50—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control
    • G03G15/5062—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control by measuring the characteristics of an image on the copy material
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
    • H04N1/40037—Circuits exciting or modulating particular heads for reproducing continuous tone value scales the reproducing element being a laser

Definitions

  • Electro-photographic printing may use one or more laser elements to write pixels onto a photo conductive medium to which colorant is then applied. Retained colorant is then applied to a print medium or an intermediate process in order to render a printed image.
  • Various aspects of the print apparatus and processes may use calibration in order to improve reproduction of the image.
  • Figure 1 is a schematic diagram of a printing apparatus according to an example
  • Figure 2 is a schematic diagram of an optical assembly of a printing apparatus according to an example
  • Figure 3 is a schematic diagram of a printed calibration image according to an example
  • Figure 4 is a flow chart illustrating a method of calibrating an imaging apparatus according to an example
  • Figure 5 is a schematic diagram of a processor and a computer readable storage medium with instructions stored thereon according to an example
  • Figure 6 illustrates calculating a derivative using different methods including according to an example
  • Figure 7 illustrates a comparison between color rendering uniformity across a printed page between known approaches and according to an example
  • Figure 8 is a flow chart illustrating a method of printing according to an example. DETAILED DESCRIPTION
  • Figure 1 shows a printing apparatus 100 according to an example. Certain examples described herein may be implemented within the context of this printing apparatus. However, it should be noted that implementations may vary from the example system of Figure 1 .
  • the printing apparatus 100 may comprise a digital offset or an electrophotographic printer (LEP) such as a laser printer.
  • LEP electrophotographic printer
  • a digital offset printer works by using digitally controlled lasers or LED imaging modules to create a latent image on a charged surface of a photo imaging cylinder or other surface.
  • the lasers are controlled according to digital instructions from a digital image file to create an electrostatic image on the charged photo imaging cylinder.
  • Colorant such as ink is then transferred to the selectively discharged surface of the photo imaging cylinder, creating an inked image.
  • the inked image is then transferred from the photo imaging cylinder to a transfer member 120, where heating evaporates a liquid vehicle from the printing fluid, and finally from the blanket cylinder to a print medium 135.
  • the printing system 100 comprises a photo imaging plate (PIP) 110.
  • the photo imaging plate 110 is mounted onto a cylinder.
  • the cylinder may comprise a holder for attaching the leading edge of the photo imaging plate 110.
  • the trailing edge of the photo imaging plate 110 is also attached to the cylinder.
  • the photo imaging plate 110 is mounted to a belt comprising a closed loop foil.
  • the mounted photo imaging plate 110 is rotatable about its axis in an anti-clockwise direction. In other examples, the photo imaging plate 110 is rotatable in a clockwise direction.
  • the optical assembly 115 operates in accordance with received image data, otherwise referred to as “print data”, “input data”, “input image data”, “print input data”, or the like.
  • the lasers may be arranged in an array.
  • An array of lasers may be embodied as individual laser elements, as multiple channels of a single laser device, as a plurality of laser devices that each have multiple channels, etc.
  • the optical assembly 115 dissipates the static charges on selected portions of the surface of the photo imaging plate 110 to leave an electrostatic charge pattern that represents an image to be printed.
  • Colorant such as ink or toner is then transferred onto the photo imaging plate 110 by at least one colorant application unit 170.
  • Colorant application units for respective colors may comprise binary ink developer (BID) units, wherein each BID unit supplies ink of a different base color.
  • BID binary ink developer
  • the colorant may contain electrically charged pigment particles which are attracted to the image areas of the photo imaging plate 110. The colorant is repelled from the non-image areas.
  • An inked or colored image of the print frame is thereby transferred onto the photo imaging plate, i.e. a representation of the image formed from colorant.
  • the colorant application unit 170 has a developer roller 175 containing charged colorant or ink at a lower bias voltage than the initial charge of the PIP 110. Therefore, colorant or ink is repelled from areas of the PIP which have not been discharged by the lasers but are attracted to the PIP in areas where this has been fully or partially discharged in proportion to the difference in voltage between the colorant on the developer roller 175 and the PIP.
  • the colorant may be charged to -450V and the PIP 110 may initially be charged to -1000V.
  • the printing apparatus 100 also comprises a transfer member 120.
  • the transfer member 120 is cylindrical. However, in other examples, the transfer member may be other shapes, e.g. a belt.
  • the cylindrical transfer member 120 is rotatable about its axis in a clockwise direction. In other examples, the transfer member 120 is rotatable in an anti-clockwise direction.
  • the transfer member 120 comprises a heated blanket wrapped around a surface of the transfer member 120.
  • the transfer member 120 may be otherwise referred to as a blanket cylinder or an intermediate transfer member.
  • the transfer member 120 is arranged to engage with the photo imaging plate 110.
  • the transfer member 120 is configured to receive a colorant or inked image from the photo imaging plate 110. In the present example, the colorant image is transferred from the photo imaging plate 110 to the transfer member 120 by rotating both the mounted photo imaging plate 110 and the transfer member 120 in opposite directions.
  • the printing apparatus 100 also comprises a media transport 130.
  • the media transport 130 is configured to move a print medium 135 relative to the transfer member 120 to enable the transfer member 120 to transfer a colorant or inked image onto the print medium 135.
  • the media transport 130 is configured to engage with the transfer member 120 to enable the colorant or inked image to be transferred from the transfer member 120.
  • the media transport 130 may be otherwise referred to as an impression cylinder or a pressure roller.
  • the image may be transferred from the transfer member 120 to the print medium 135 as the print medium 135 passes to a nip between the transfer member 120 and the pressure roller 130.
  • the printing apparatus 100 comprises a controller 140 which controls the optical assembly 115, the voltage applied to the PIP 110 by the charged roller 180 and/or the voltage applied to the colorant on the developer roller 175.
  • the controller 140 comprises a processor 160 and a memory 150.
  • Processor 160 can include a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.
  • the memory 150 may comprise volatile and/or nonvolatile memory.
  • the memory 150 may comprise dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and/or flash memories.
  • DRAMs or SRAMs dynamic or static random access memories
  • EPROMs erasable and programmable read-only memories
  • EEPROMs electrically erasable and programmable read-only memories
  • flash memories flash memories
  • a data structure may comprise various settings for the printing apparatus, for example according to its type, and may provide for example set points for the above mentioned voltages and well as a nominal laser power.
  • the nominal laser power level (100%) may be set to print a color at a predetermined color printing parameter, such as a dot area density (DA) of 50%.
  • DA dot area density
  • Another data structure may comprise adjustment or compensation factors useable to adjust different operational parameters of the printing apparatus over its lifetime. For example the above mentioned voltages or nominal laser power may be varied over the lifetime of the printing apparatus, for example to compensate for component wear. Different adjustment factors in a given data structure may be useable to adjust the power level or other parameters of different ones of the plurality of optical elements. Therefore, each of the plurality of optical elements in the optical assembly 115 may be independently adjustable using a corresponding adjustment factor.
  • the uniformity of rendered color in a printed image may also vary across a print area, corresponding to locations on a printed image. This may be caused by imperfections in optical components, dirt or dust accumulation in different areas, charge leakage in different areas of the PIP 150 or voltage differences applied across the developer roller 175.
  • a data structure may be used to store adjustment or compensation factors which correspond to different locations or spatial coordinates of a print area such as a page of substrate such as paper. The adjustment may then be applied to the laser power when the laser is directed at a corresponding spatial coordinate of the PIP 110.
  • the adjustments may be provided in the form of a look-up table (LUT) with adjustments provided according to spatial coordinates.
  • LUT look-up table
  • the printing apparatus 100 also comprises a sensor 190 which is configured to measure one or more color rendering parameters from a recently printed image on the substrate 135.
  • the sensor may measure gray levels at different locations of a printed calibration image in order to allow a comparison of the measured levels and those expected according to the grey levels provided in corresponding locations of calibration image data.
  • the senor or measurement unit 190 may comprise an in-line camera, in-line scanner, in-line spectrophotometer, or similar device. In other examples the sensor 190 may be separate from the printing apparatus 100 but configured to forward the optical properties of images printed by the printing apparatus in order to calculate the adjustments, or to provide the adjustments directly.
  • the processor 160 may be configured to apply the spatial and other adjustments to the printing apparatus when printing an image in order to improve image quality, including uniformity of color rendering. Different adjustments may be applied for different colors, for example cyan, yellow and magenta.
  • the processor may also be configured to determine the spatial adjustments for storing in the memory 150 using the measured values from the sensor 190.
  • a gray level for an image region may be determined by obtaining digital halftone values from the input image data and averaging the digital halftone values of pixels across an area of the image.
  • a gray level for an image region is determined by obtaining a set of optical power parameters for each pixel in the image region.
  • Measuring gray level for a printed image area may comprise averaging measurements of pixels across the area.
  • the area size can be tuned to the resolution of the printing apparatus and/or the sensor. For example, the area size may be based on the resolution of the sensor (which is often the lowest of the two) and ensuring enough sensor pixels in the area to enable averaging of the measured gray levels.
  • Figure 2 shows an optical assembly 200 according to an example. Some items depicted in Figure 2 are similar to items shown in Figure 1. Corresponding reference signs, incremented by 100, are therefore used for similar items.
  • the optical assembly 200 of a printing apparatus comprises a photo imaging plate 210 mounted on a rotatable cylinder.
  • An exposure unit 215 comprising an array of lasers 216 is controlled by controller 240.
  • the controller 240 is configured to obtain adjustment factors for one or an the array of lasers 216 as described above.
  • the controller 240 may also be configured to control the voltage of a charge roller 280 on order to control the bias voltage applied to the PIP 210.
  • the optical assembly 200 also comprises a polygon mirror 217.
  • the exposure unit 215 comprises the polygon mirror, for example as one of a plurality of optical elements of the exposure unit 215.
  • the polygon mirror 217 is separate from the exposure unit 215.
  • the polygon mirror 217 may be configured to scan the or an array of lasers 216 across a surface of the photo imaging plate 210 in a scan direction 235, for example via rotation of the polygon mirror 217.
  • the laser 216 and the polygon mirror 217 may be arranged to write successive swathes 218, 219 across the surface of the photo imaging plate 210.
  • Figure 2 schematically shows completed swathes 218 and a swathe in the process of being written 219.
  • the mounted photo imaging plate 210 may rotate about its axis in order to allow successive swathes to expose different parts of the surface of the photo imaging plate 210. Rotation of the photo imaging plate 210 may correspond to a media transport direction 230, which may be perpendicular to the scan direction 235.
  • Each swathe may have a number of lines equal to the number of lasers. For simplicity, a single of laser 216 is shown in Figure 2, however other numbers of lasers could be used, for example an array may include 3, 12, 18, 28, 36 or 40 lasers.
  • the laser 216 may be scanned across the surface of the photo imaging plate 210 using means other than a polygon mirror, for example by using phased array scanning techniques, refractive optical components, acousto- optical deflectors or electro-optic deflectors.
  • the power received from a laser 216 at the surface of the photo imaging plate 210 may vary across a swathe, in the scan direction 235, due to differences in the optical path as the lasers are scanned across the photo imaging plate 210, for example. Differences in the optical path may be due to the optical design or production tolerances of the optical elements being used. Further, the power received from a laser at the surface of the photo imaging plate 210 may vary between different swathes, for example due to variations in optical properties between different facets of polygon mirror 217. Variation in received laser power may lead to differences in the optical spot shape on the surface of the photo imaging plate 210 across a swathe and/or between different swathes. This may result in dot area non-uniform ity in a printed image. This may, in turn, lead to visible artifacts in the printed image.
  • individual laser elements of an array may be controllable independently of image data.
  • a format correction feature may be provided that allows laser power to be varied along the scan direction.
  • format correction allows the power of each laser to be independently varied at intervals along the scan direction 235.
  • the intervals each correspond to 1 mm along the scan direction 235.
  • the intervals each correspond to 10 mm along the scan direction 235.
  • the format correction feature may be implemented by controlling a current provided to each laser element in each interval.
  • a pulse width of the laser is controlled instead of, or in addition to, the current provided to the laser.
  • the laser profile to be applied using format correction is controlled as 1 st or 2 nd order polynomials, with parameters of the polynomials being selected to reduce or minimize measured artifacts according to a trial-and- error approach.
  • a two-dimensional array or data structure indicative of the corrections to be applied to the lasers using format correction may be stored, for example to a file, and loaded on demand when format correction is to be applied.
  • One dimension of the array may correspond to a location along a scan direction, and the other dimension of the array may correspond to the laser element in the array of laser elements.
  • such correction data comprises a third dimension corresponding to a facet of a polygon mirror.
  • a given data structure comprises corrections for 40 lasers and 6 polygon facets at 100 predetermined locations along the scan direction.
  • a power of a laser element may be adjusted by a first correction factor and a second correction factor.
  • the first correction factor corresponds to the laser element.
  • the second correction factor corresponds to the polygon facet.
  • interpolation may be performed between correction factors for the locations that are the nearest neighbors of the given pixel.
  • Variation in received power between lasers may lead to a lack of uniformity in the final printed image.
  • Optical power density non-uniform ity may lead to non-uniform ity of the dot area on the print medium.
  • Non-uniform ity between laser elements may lead to periodic disturbances in the final image, for example scan band artifacts and lack of color uniformity.
  • Such variation can be caused by differences between the individual laser elements or between different facets of a rotatable polygon mirror, but may also be caused by interference or crosstalk between the lasers during operation. Calibration of the lasers may be performed on individual lasers in an array.
  • this may not address variation in laser output due to interference or crosstalk between the lasers, since this occurs when multiple lasers of the array are operated together and does not occur when the lasers are operated separately. Additionally, differences between optical characteristics of the lasers may contribute to dot area variation between lasers in a swathe. Furthermore, in order to achieve a high printed resolution, the number of lasers in an exposure unit may be increased, for example to 40 lasers, and the spacing between adjacent lasers in an array may be reduced. The density of screen coverages may also be increased in order to achieve a higher resolution. Consequently, interactions between different lasers and/or with the screen data can become complex and may lead to dot area variation between lasers and/or between different polygon facets being dependent on the gray level or coverage that is being used.
  • the banding profile of the array of lasers is different for different gray levels due to thermal effects and/or electrical cross-talk of the lasers.
  • Dot area variation may be different for different gray levels but may not be directly proportional to the gray level being used, and therefore may not be obtainable via a constant or known factor. Banding artifacts for different gray levels are therefore difficult to predict due to the complexity of the interactions and effects of the simultaneously- used laser elements.
  • dot area variation between different polygon mirror facets also behaves differently for relatively sparse or relatively dense screen or gray coverages.
  • Figure 3 shows a printed calibration image 300 according to an example.
  • the printed calibration image 300 may be generated by printing apparatus 100.
  • Generating the calibration image 300 may involve controlling one or more laser elements of an optical exposure unit, such as the exposure unit of optical assembly 200.
  • the calibration image 300 may be generated as part of a calibration operation.
  • the calibration operation may be performed in order to generate sets of correction factors or adjustments to be applied to the or each laser element depending on a spatial coordinate or area to which it is directed.
  • the printed calibration image 300 comprises a plurality of areas 310 printed at a common tone level, for example 50% dot area density or a gray level (GL) of 150 in a 8-bit tone level system. This corresponds to a nominal optical power level (100%).
  • the measured gray levels may vary spatially both across and down the printed image.
  • the measured gray levels may vary across the printed calibration image by several gray levels, for example the measured gray levels (GL) may range from GL 135 to 168 in an 8-bit color system. It can also be seen that the change in tone level varies slowly (low frequency) between adjacent areas, for example the measured tone level between areas 31 Ox and 31 Oy may vary between GL 155 and 158 in an 8-bit color system.
  • a first row of a modified printed calibration image 350 is also illustrated.
  • This modified printed calibration image 350 corresponds to the first row of calibration image 300, however instead of using the same optical power level (100%) for the lasers for each area 310, different power levels are used for different areas.
  • a first power level e.g. 110% of the nominal power
  • a second power level e.g. 90%
  • Areas having the higher optical power level are indicated using 360 and areas having the lower optical power level are indicated using 370.
  • Using different optical power levels enables more accurate spatial adjustments to be determined as will be described in more detail below.
  • first optical power level above a nominal power level and a second optical power level below a nominal power level Whilst the example of using a first optical power level above a nominal power level and a second optical power level below a nominal power level, alternative arrangements are possible. For example, both the first and different second power levels may be above or below the nominal power level, or one of the first and second power levels may be set at the nominal optical power level.
  • the optical element 215, 217 may be associated with a range of optical power levels (LP) to reproduce the range of grey levels (e.g. In Line Scanner range in GL may be 0 to 255) for example 80% to 120% of a nominal or central optical power level.
  • LP optical power levels
  • the relationship between GL and LP may not be linear across the entire range and so the first and second power levels may be selected from within this range but away from the ends, for example 90% and 110%.
  • Such a selection of different LP may well represent the whole range.
  • the selection of different power levels may average to the nominal power optical level. In other arrangements, more than two different power levels may be used. For example, measurements may be made across three adjacent areas using an LP of 85%, 100%, 110% or 60%, 100%, 120%. Alternative LP are also possible.
  • the modified printed calibration image 350 may be measured, for example by the sensor 190. Measuring the printed calibration image 350 may comprise measuring an optical property of the area 310 in the modified calibration image 350.
  • the measured optical property may include gray values of the image measured by an inline scanning device, for example.
  • the measurement may include scanning an image and evaluating a gray level value at each pixel (or each pixel of an area 310) of the scanned image. For example, where the scan has 8 bits per pixel, each pixel may have a value from 0 to 255, with 0 representing black and 255 representing white.
  • the scanning is performed in a 535x600 dots- per-inch mode (vertical x horizontal), although other scanning modes may be used in other examples.
  • Figure 4 shows a method 400 of calibrating electro-photographic printing according to an example.
  • the method 400 is performed by a controller such as controller 140, 240.
  • the optical controller may perform the method based on instructions retrieved from a computer-readable storage medium.
  • the photo imaging plate may comprise photo imaging plate 110 and the developer unit may comprise developer unit 170.
  • a nominal optical power level is identified, for example by reference to a look up table (LUT).
  • the nominal power level may correspond to a calibration target or predetermined color rendering parameter level.
  • algorithm defines average GL as the target for the entire page for uniformity sake, for example or a wanted light reflectance level.
  • An example printer apparatus has a nominal optical power around 1.1 uJ/cm A 2, although different printer apparatus calibrations and settings may influence this.
  • the calibration may be performed for different nominal power levels or different target gray levels, for example calibration may be performed for nominal power levels associated with aGL of 128, 64 and 192 in order to improve color uniformity across the full range of tones.
  • Nominal PL is basically the same for all range of tones (DAs) The difference is in the digital image that may cover less or more of the area, resulting in different GL
  • a predetermined color printing parameter for calibration is similarly identified, for example 50% dot area density (DA) may be used. Other values may be used, for example 25% or 75% DA. In other examples calibration may be performed across a number of DA for better uniformity, with intermediate DA utilizing interpolation between samples values. In other examples, a color printing parameter other than DA may be used.
  • DA dot area density
  • the method prints a calibration image at the predetermined color printing parameter (e.g. 50% dot area density) but using different optical power levels for adjacent areas. For example, one area may be printed at 90% of nominal laser power whilst an adjacent area may be printed at 110% of nominal laser power.
  • the printed calibration image 350 may resemble that shown in the lower part of Figure 3.
  • the method measures the color rendering parameter levels or properties, for example gray level, for the printed calibration image at the different areas. Because different laser power levels are used, the difference in measured gray level between areas is greater than it would be if the same laser power level had been used. This enables improved spatial adjustment accuracy as will be described below. In other examples, different color rendering properties could additionally or alternatively be used, for example light reflectance.
  • a derivative is calculated for each area using the measured color rendering parameter level for the area and the measured color rendering parameter for an adjacent area. By using gray level measurements for the area of interest and an adjacent area to calculate the derivative, this can be determined using a single printed calibration image.
  • the use of different optical power levels for two areas used to determine a derivative improves the accuracy of the calculation.
  • the derivative is the relationship (or a conversion factor) between gray level (GL) and laser power level (LP).
  • GL may vary spatially for the same LP. Therefore, a measurement may be made for each spatial area of a printed calibration image in order to determine the derivative for that area.
  • Figure 6c shows an approach according to an example of the disclosure.
  • the calculated derivative is used to determine an adjustment or correction factor for the optical power level associated with respective areas. For example, if the slope of the derivative for an area is -1 .2, and the measured color rendering parameter level (e.g. GL) of this area is 4GL above the average GL of the printed calibration image, then LP is increased to 4.8%. This may be expressed by:
  • the method determines whether a further iteration is to be carried out. This may be determined using a threshold, for example that at least 90% of the measured gray levels are within 2% of the gray level setting of 150. If the threshold is met, the method moves to item 440. If the threshold is not met, the method moves to item 430 where the previously determined adjustments for each area are applied to the optical power settings for the next iteration. At item 435, the method returns to item 410 to repeat the calibration process.
  • a threshold for example that at least 90% of the measured gray levels are within 2% of the gray level setting of 150.
  • the method determines whether calibration for other colors is to be carried out and if so, moves to item 445 where the method then returns to item 405 where a new optical power level for the new color is identified, and the calibration process is repeated. Otherwise, at item 450 the method stops.
  • Figure 7 illustrates a comparison of a known approach using multiple calibration print/scan iterations together with a nominal laser power setting for each area, and an approach according to an example using a single iteration together with different laser power settings for adjacent areas.
  • the y-axis represents the convergence percentage, for example the percentage of GL measurements within 2% of the original gray level setting, e.g. 150.
  • the PIP circumference covers two developing cycles, finally printing two images (on two sheets in Simplex case, or two sheet sides in case of Duplex printing).
  • the same color is printed on both sides. To achieve the same color, different voltages or different LP may be applied.
  • the right most bar for each color represents a method according to an example. It can be seen that for each color, the convergence percentage is close to 100% on the first iteration.
  • the left most bars represent a standard known method, with each color requiring two or more iterations to achieve the desired 90% convergence percentage threshold.
  • the strong performance enables tightening of the color uniformity specification and could allow for open-loop calibration, further improving perceived print quality, as well as operational performance in terms of reduced time and resources such as substrates used.
  • FIG. 5 illustrates a controller 500 which may be used to implement a method of electro-photographic printing or a printing apparatus according to an example. These may be used to determine adjustments for the optical power level used to print different areas, that is to provide spatial adjustments of laser power to compensate for spatial variations in reproduced gray level or other color rendering property across a print area.
  • the controller 500 comprises a processor 510 connectably coupled to the computer-readable storage medium 520.
  • the processor 510 may be a processor of a printing apparatus similar to printing apparatus 100.
  • the processor 510 is a processor of a controller such as controller 140.
  • the computer-readable storage medium 520 may be arranged to implement certain examples described herein.
  • the computer-readable storage medium 520 comprises a set of computer-readable instructions 530 stored thereon.
  • the computer-readable instructions 530 may be executed by the processor 510.
  • Instruction 540 instructs the processor 510 to determine an optical power level associated with a predetermined color rendering property for the current calibration. For example a nominal laser power level 100% may be associated with a target gray level of 150. The nominal optical power level may be determined by reference to a LUT in memory 520. In some examples, a calibration image may be printed using the identified optical power level together with a predetermined color printing parameter such as a default dot area setting DA. The DA setting may also be determined by reference to a LUT.
  • the nominal optical power level may depend on the type of printing apparatus to which the calibration method is applied, and may also depend on other factors such as printing apparatus lifetime and measured properties such as ambient temperature, developer voltage, corona wire voltage and other operational parameters associated with the printing apparatus as well as mechanical pressures and distortion of the drums.
  • the predetermined printing parameter may be a standard used for calibration.
  • Instruction 550 instructs the processor 510 to determine measured color rendering properties such as gray levels (GL) for a calibration image printed at the predetermined color printing parameter but with different optical power levels.
  • Instruction 560 instructs the processor 510 to determine an adjustment for the optical power level corresponding to an area of the printed calibration image using measured color rendering properties (e.g. GL) at a first area and a second area.
  • the adjustment may be determined by calculating a derivative for each area as previously described, and using this to find a corresponding adjustment for each area. This adjustment can then be applied to the optical power level associated with a corresponding spatial location in the PIP and/or printing area.
  • Processor 510 can include a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.
  • the computer-readable storage medium 520 can be implemented as one or multiple computer-readable storage media.
  • the computer-readable storage medium 520 may include different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy and removable disks; other magnetic media including tape; optical media such as compact disks (CDs) or digital video disks (DVDs); or other types of storage devices.
  • DRAMs or SRAMs dynamic or static random access memories
  • EPROMs erasable and programmable read-only memories
  • EEPROMs electrically erasable and programmable read-only memories
  • flash memories magnetic disks such as fixed,
  • the computer-readable instructions 530 can be stored on one computer-readable storage medium, or alternatively, can be stored on multiple computer-readable storage media.
  • the computer-readable storage medium 520 or media can be located either in the printing apparatus 100 or located at a remote site from which computer-readable instructions can be downloaded over a network for execution by the processor 510.
  • Figure 8 illustrates a method 800 of electro-photographic printing according to an example.
  • the method 800 may be performed by a controller such as controller 140, 240, 500 in order to control and printing apparatus such as that described with respect to Figures 1 and 2.
  • the optical controller may perform the method based on instructions retrieved from a computer- readable storage medium.
  • a nominal optical power level in a printer 100 is identified, for example by reference to a look up table (LUT).
  • a calibration page is printed using a predetermined color printing parameter (e.g. 50% DA) at different optical power levels. For example, where the nominal optical power level is assigned 100%, the calibration page may be printed at 90% and 110% at adjacent alternating areas.
  • a predetermined color printing parameter e.g. 50% DA
  • color rendering parameter levels e.g. GL are measured for the printed calibration image. These may be measured for different areas of the calibration image.
  • an adjustment is determined for the optical power level associated with an area of the printed calibration image using measured color rendering parameter levels (e.g. GL) associated with the area.
  • the measured color rendering parameter levels associated with the area being printed at different optical power levels. For example, a GL measured for the area and a GL measured for an adjacent area may be used. This enables adjustments for different printing areas to be determined using a single printed calibration image. In another example, GLs measured for the same area but different printed calibration images may be used.
  • Certain examples described herein enable multiple sets of corrections to be applied to optical elements or lasers of a printing system for different regions in an image.
  • the accuracy of these corrections for low gray coverage regions can be improved by determining these using a calibration image printed with increased contrast.
  • the improved accuracy of the corrections for low gray coverage regions reduces visible printing artefacts such as banding.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Color, Gradation (AREA)

Abstract

Certains exemples décrits dans le présent document concernent un procédé d'étalonnage d'impression électro-photographique. Dans un exemple, il est fourni un procédé d'impression électro-photographique. Le procédé identifie un niveau de puissance optique nominal dans une imprimante et associé à l'impression d'une image d'étalonnage à un niveau de paramètre de rendu des couleurs prédéterminé, et imprime l'image d'étalonnage en utilisant un paramètre d'impression des couleurs prédéterminé à différents niveaux de puissance optique. Les niveaux de paramètres de rendu des couleurs sont mesurés pour l'image d'étalonnage imprimée, et un ajustement est déterminé pour le niveau de puissance optique associé à une zone de l'image d'étalonnage imprimée en utilisant les niveaux de paramètres de rendu des couleurs mesurés associés à la zone, les niveaux de paramètres de rendu des couleurs mesurés associés à la zone étant imprimés à différents niveaux de puissance optique.
PCT/US2021/057306 2021-10-29 2021-10-29 Étalonnage d'imprimante WO2023075788A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050046655A1 (en) * 2003-08-26 2005-03-03 Eastman Kodak Company Method for calibration of a laser thermal halftone printer
US20090067007A1 (en) * 2007-09-10 2009-03-12 Canon Kabushiki Kaisha Calibration method and printing apparatus
US20190149699A1 (en) * 2016-07-20 2019-05-16 Hp Indigo B.V. Printing system calibration
US20190268503A1 (en) * 2016-10-20 2019-08-29 Hp Indigo B.V. Obtaining print data

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050046655A1 (en) * 2003-08-26 2005-03-03 Eastman Kodak Company Method for calibration of a laser thermal halftone printer
US20090067007A1 (en) * 2007-09-10 2009-03-12 Canon Kabushiki Kaisha Calibration method and printing apparatus
US20190149699A1 (en) * 2016-07-20 2019-05-16 Hp Indigo B.V. Printing system calibration
US20190268503A1 (en) * 2016-10-20 2019-08-29 Hp Indigo B.V. Obtaining print data

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