WO2012160346A1 - Appariement de couleurs - Google Patents

Appariement de couleurs Download PDF

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Publication number
WO2012160346A1
WO2012160346A1 PCT/GB2012/051031 GB2012051031W WO2012160346A1 WO 2012160346 A1 WO2012160346 A1 WO 2012160346A1 GB 2012051031 W GB2012051031 W GB 2012051031W WO 2012160346 A1 WO2012160346 A1 WO 2012160346A1
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WO
WIPO (PCT)
Prior art keywords
printing condition
printing
grey balance
source
colour
Prior art date
Application number
PCT/GB2012/051031
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English (en)
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WO2012160346A8 (fr
Inventor
Lee BADHAM
Original Assignee
Bodoni Systems Ltd
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Publication date
Application filed by Bodoni Systems Ltd filed Critical Bodoni Systems Ltd
Publication of WO2012160346A1 publication Critical patent/WO2012160346A1/fr
Publication of WO2012160346A8 publication Critical patent/WO2012160346A8/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
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/12—Digital output to print unit, e.g. line printer, chain printer
    • G06F3/1297—Printer code translation, conversion, emulation, compression; Configuration of printer parameters
    • 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
    • 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
    • H04N1/6077—Colour balance, e.g. colour cast correction

Definitions

  • the invention relates to colour matching in printing operations. Background to the invention
  • Printing units generally produce printed images by applying a combination of differently coloured base colourants onto a substrate. For example, it is common to apply a combination of cyan, magenta, yellow and black (CMYK) colourants to a substrate in order to create a colour image.
  • CMYK cyan, magenta, yellow and black
  • the appearance of the printed image can be varied as required.
  • the combinations and patterns of the printed base colourants are generally specified in a printing instruction which is supplied to the printing unit.
  • the printing instruction may, for example, specify the amount of each individual base colourant that should be printed onto the substrate and the locations at which it should be printed in order to produce the image.
  • the amount, or dot ratio, of each individual base colourant (e.g. CMYK) may be represented in the printing instruction by a numerical value for each colourant.
  • the different appearance of the images may be caused by the individual base colourants, such as the cyan, magenta, yellow and black inks or toner, varying slightly in colour from printing unit to printing unit. For example, manufacturing tolerances may result in different batches of yellow colourant having slightly different colour properties to each other. The same may apply to any or all of the other individual colourants. These colour differences may be increased still further when different colourant manufacturers are used.
  • the individual base colourants such as the cyan, magenta, yellow and black inks or toner
  • the colours of the individual colourants may also be dependent on temperature and other environmental factors. This makes it challenging to consistently reproduce a colour image even in a situation where the same printing unit and colourants are being used.
  • colour management In order to accurately reproduce the same image using different printing units and/or under different printing conditions, it is necessary to tailor the printing instruction to the printing unit and the conditions being used. This is often referred to as colour management. Several colour management techniques exist.
  • a first of the existing colour management techniques revolves around the use of ICC profiles. These describe how a particular device inputs colour, for example in the case of a scanner or camera, or outputs colour, such as in the case of a printing press, inkjet printer or other printing unit when printing onto a particular substrate.
  • the ICC profiles connect individual base colourant combinations, such as a particular set of CMYK values, to colour values in a standard colour space such as CIE LAB or CIE XYZ.
  • the standard colour space provides a 'profile connection space' across which a printing instruction can be tailored to take account of the characteristics of a particular printing unit and the conditions being used for printing.
  • the numerical CMYK values of a source printing instruction can be adapted so that the printed CMYK values will more accurately represent the colour of the image.
  • a known technique is to print a colour chart of between approximately 800 and 1600 patches, which generally occupies substantially the whole area of an A4 or A3 sized substrate. The patches represent colours across the visible spectrum. Once printed, the colour of each patch is measured in a profile connection space, such as CIE LAB, using suitable equipment. This allows conversions between the known combinations of printed base colourants (e.g. individual sets of CMYK values) and colour values in the profile connection space (e.g. L*a*b* values) to be made for the printing unit concerned.
  • a look up-table can be compiled which links sets of printable CMYK values to L*a*b* values in the CIE LAB profile connection space.
  • An interpolation process can be used to determine profile connection space values (e.g. L*a*b* values) for sets of CMYK values which have not been printed as a colour patch in the measured chart. If the number of measured patches is too low, for example less than 800, the accuracy of this interpolation process can be unreliable in certain colour regions and thus the quality of the printed images is unsatisfactory. The process on the whole is both time- consuming and expensive. Furthermore, the large number of patches required for accurate colour
  • a second existing colour management technique is to define a target printing condition using CIE LAB references for the colours of the primary colourants (e.g. CMYK) and Tonal Value Increase (TVI) for the tint percentages.
  • the actual printing condition of the printing unit can then be adjusted and aligned to the target values.
  • This technique is used in the 'pressSIGN' colour management software produced by Bodoni Systems.
  • a problem with the technique is that it can be difficult to adjust the colours of the primary colourants, particularly in digital printing processes which use pre-manufactured toner.
  • a third existing colour management methodology is called Neutral Print Density.
  • the method involves setting target colour values for the primary colourants and having a predefined density target for Cyan, Magenta and Yellow.
  • the method is known to be slow and requires a separate print run to setup and perform. It is only suitable for use on a litho press, where density adjustments are relatively easy to perform.
  • the invention provides a faster, simpler, more flexible and less expensive technique for accurately producing images having the desired colour appearance.
  • a method of reproducing a colour image comprising identifying a grey balance of a source printing condition of an image file to be printed, identifying a printing condition of a printing unit to be used to print the image file, converting the grey balance of the source printing condition to a grey balance of the printing condition of the printing unit, establishing a difference between the grey balance of the source printing condition and the grey balance of the printing condition of the printing unit and applying the established difference to colour values in the image file to produce a set of colour values to be printed at the printing unit.
  • the grey balance of the source printing condition may comprise a first value of black
  • the grey balance of the printing condition of the printing unit may comprise a second value of black
  • the difference between the grey balances may comprise the difference between the first value and the second value.
  • the grey balance of the source printing condition may comprise a first value of cyan
  • the grey balance of the printing condition of the printing unit may comprise a second value of cyan
  • the difference between the grey balances may comprise the difference between the first value and the second value.
  • the grey balance of the source printing condition may comprise a first value of magenta
  • the grey balance of the printing condition of the printing unit may comprise a second value of magenta
  • the difference between the grey balances may comprise the difference between the first value and the second value.
  • the grey balance of the source printing condition may comprise a first value of yellow
  • the grey balance of the printing condition of the printing unit may comprise a second value of yellow
  • the difference between the grey balances may comprise the difference between the first value and the second value.
  • Applying the established difference to colour values in the image file may comprise adding or subtracting the difference between the colour values of the grey balance of the source printing condition and the colour values of the grey balance of the printing condition of the printing unit to or from the colour values in the image file.
  • Establishing the grey balance of the source printing condition may comprise reading the printing condition of the image to be printed to determine
  • the defined profile connection space values of the grey balance may be L*a*b* values.
  • Identifying a printing condition of the printing unit to be used to print the image file may comprise printing a plurality of CMYK colour patches and measuring the colour of the colour patches in a profile connection space.
  • Converting the grey balance of the source printing condition to the grey balance of the printing condition of the printing unit may comprise inputting, to a colour matching module, the source printing condition, the printing condition of the printing unit, a rendering intent and one or more profile connection space values of the grey balance of the source printing condition; receiving from the colour matching module one or more profile connection space values of the grey balance of the printing condition of the printing unit; and reading, from the source printing condition, one or more combinations of non-black colourants which correspond to the one or profile connection space values of the grey balance of the printing unit.
  • Establishing the difference between the grey balance of the source printing condition and the grey balance of the printing condition of the printing unit may comprise identifying the difference between a combination of non-black colourants corresponding to the grey balance of the source printing condition and a combination of non-black colourants corresponding to the grey balance of the printing condition of the printing unit.
  • the source printing condition may be an ICC profile.
  • the image to be printed may contain a CMYK ICC profile or has a known set of colour characteristics.
  • an apparatus configured to reproduce a colour image, comprising: means for identifying a grey balance of a source printing condition of an image file to be printed; means for identifying a printing condition of a printing unit to be used to print the image file; means for converting the grey balance of the source printing condition to a grey balance of the printing condition of the printing unit; means for establishing a difference between the grey balance of the source printing condition and the grey balance of the printing condition of the printing unit; and means for applying the established difference to colour values in the image file to produce a set of colour values to be printed at the printing unit.
  • the apparatus may comprise means for performing a method as recited in any of claims 2 to 14.
  • an apparatus comprising: at least one processor; at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: identify a grey balance of a source printing condition of an image file to be printed; identify a printing condition of a printing unit to be used to print the image file; convert the grey balance of the source printing condition to a grey balance of the printing condition of the printing unit; establish a difference between the grey balance of the source printing condition and the grey balance of the printing condition of the printing unit; and apply the established difference to colour values in the image file to produce a set of colour values to be printed at the printing unit.
  • Figure 1 is a schematic illustration of an apparatus for printing an image specified according to a source printing condition
  • figure 2 is a flow diagram showing a method of printing an image file having a source printing condition using a printer having a destination printing condition which is different to the source printing condition;
  • figure 3 is an illustration of curve data representing lightness values for CMY overprint tints between 0 and 100;
  • figure 4 is another illustration of curve data representing lightness values for CMY overprint tints between 0 and 100;
  • figure 5 is an illustration of an adjustment curve for converting black colourant values in a source printing condition of an image file to black colourant values in a destination condition of a printing unit;
  • figure 6 is an illustration of an adjustment curve for converting cyan colourant values in a source printing condition of an image file to cyan colourant values in a destination printing condition of a printing unit;
  • figure 7 is an illustration of an adjustment curve for converting magenta colourant values in a source printing condition of an image file to magenta colourant values in a destination printing condition of a printing unit; and figure 8 is an illustration of an adjustment curve for converting yellow colourant values in a source printing condition of an image file to yellow colourant values in a destination printing condition of a printing unit.
  • a method and apparatus 1 for accurately reproducing a colour image specified in an input printing instruction is described below.
  • the controller 2 may be configured to operate under the control of computer readable code so that, when executed by the one or more processors 3, the computer readable code causes the processor(s) 3 to adjust an image file for printing in accordance with the method described below.
  • the computer readable code may be stored on a memory medium 4 of the apparatus 1 or may be stored in an external memory.
  • the memory medium 4 may comprise ROM, RAM or any other suitable storage means.
  • the apparatus 1 is electronic and is preferably comprised in a printing unit 5 such as a printing press, laser printer or inkjet printer. However, the apparatus 1 may alternatively be comprised externally from the printing unit 5. In this case, the printing unit 5 and external apparatus 1 are communicatively coupled so that the apparatus 1 can send printing instructions to the printing unit 5 during a printing operation. Communication between the external apparatus 1 and printing unit 5 may take place wirelessly or using a suitable communication cable.
  • the apparatus 1 is configured to receive a source image file which describes an image to be printed.
  • the source image file may, for example, be input to the apparatus 1 from an external source such as a computer.
  • image files for printing are prepared according to a selected 'source' printing condition.
  • the source printing condition is selected by the creator of the image file and is generally an ICC profile, although other types of printing condition are also possible.
  • the source printing condition can rarely be matched at the printing unit 5 which is to be used to print the image and so direct printing of the source image file results in distorted or non-optimum colour in the printed image, as explained previously.
  • the apparatus 1 reads the source printing condition from the source image file and, optionally, stores the source printing condition in the memory 4.
  • the source printing condition is the ICC profile: 'ISO 12647-2, coated' .
  • any suitable printing condition such as a different ICC profile, could alternatively be used.
  • the apparatus 1 determines the grey balance of the source printing condition.
  • the grey balance of the source printing condition corresponds to one or more
  • the source printing condition is an ICC profile
  • the ICC profile can be read by the apparatus 1 to determine one or more combinations of non-black colourants which correspond to a defined grey balance value in a profile connection space such as CIE LAB. This is discussed in detail below.
  • Any suitable profile connection space can be used as an alternative to CIE LAB, for example CIE LCH, CIE LUV or CIE XYZ.
  • the grey balance of the source printing condition is defined, using the CIE LAB profile connection space, as combinations of non-black (CMY) colourants which have a* and b* values that are equal to a* and b* values of the black colourant (K).
  • This method of defining grey balance using the a* and b* values of the black colourant (K) will be used in the subsequent discussion.
  • other definitions of grey balance could alternatively be used. Examples include defining grey balance as one or more mixes of non-black colourants (e.g. CMY) which have a* and b* values of zero, or defining grey balance based on the a* and b* values of the substrate onto which the image is to be printed. Paper is likely to be the most commonly used substrate, although any suitable substrate is possible.
  • Table A An example of a plurality of combinations of non-black colourants which correspond to the grey balance of the source printing condition, ICC profile: 'ISO 12647-2 coated' , is shown in Table A below. Specifically, Table A shows the combinations of non-black colourants (CMY) which have a* and b* values that are most closely matched to the a* and b* values of a plurality of tint percentages of black colourant (K). In this example, three tint percentages of black colourant (K) are used: 25%, 50% and 75%.
  • the CMY combinations are identified by the apparatus 1 from the ICC profile: 'ISO 12647-2, coated' .
  • CMY combinations given in Table A represent the correct grey balance of the source printing condition, 'ISO 12647-2, coated' .
  • the first column of Table A represents tint percentages of black colourant (K) whilst the second, third and fourth columns represent their corresponding L*a*b* values in the CIE LAB profile connection space.
  • the L*a*b* values of the black colourant for any particular tint percentage can be obtained from look-up tables in the ICC profile: 'ISO 12647-2, coated' using known techniques.
  • the fifth, sixth and seventh columns of Table A specify the combinations of non- black colourants, in this case values of CMY, which most closely match the grey balance of the source printing condition. As already discussed, in this example three CMY grey balance combinations are found which respectively correspond to the a* and b* values of three different tint percentages of black (K).
  • CMY combinations which correspond to the a* and b* values of a correspondingly greater number of tint percentages of black colourant. If the grey balance is defined in a different way, for example as the combinations of non-black colourants which have a* and b* values of zero, then a corresponding step is performed to look up the relevant CMY colourant combinations which mostly closely match the defined grey balance.
  • the apparatus 1 may identify the combinations of non-black colourant (CMY) which correspond to the L*a*b* grey balance values using an iteration process. For example, the apparatus 1 may iterate through all possible CMY combinations in the source printing condition, in this case the ICC profile: 'ISO 12647-2 coated' , to find the CMY combinations that are most closely matched, in terms of their values in the CIE LAB profile connection space, to the selected black tint (K) percentages.
  • K black tint
  • a known technique can be used.
  • the apparatus 1 may be configured to evaluate colour difference in terms of ⁇ (deltaE) and select the CMY combination for which the ⁇ between the relevant tint percentage of black (K) and the CMY combination is least. Look-up tables in the source printing condition can be used to determine the L*a*b* values of any CMY combination using known techniques.
  • the apparatus 1 causes a colour bar to be printed at the printing unit 5.
  • the colour bar comprises a plurality of colour patches, each of which is made up of known combinations of non-black and black colourants (CMY and CMYK). More specifically, in this example, each printed patch corresponds to a known set of printed CMYK or CMY values, which may be stored in the memory 4 associated with the apparatus 1.
  • the colour bar may also include a blank patch in which no colourant is printed.
  • the apparatus 1 may, for example, supply a printing instruction to the printing unit 5 instructing the printing unit 5 to print the patches.
  • the printing instruction comprises a particular CMYK or CMY dot percentage ratio for each patch.
  • the number of colour patches in the colour bar is significantly less than the prior art method of using a colour chart described previously.
  • An example is a colour bar containing approximately forty colour patches.
  • the number of patches in the colour bar can be limited to the number of patches which is sufficient to evaluate the combinations of CMY which will produce a neutral grey, i.e. the grey balance, when printed under the destination printing conditions. This is explained in more detail below.
  • An example set of printable CMYK values for a forty patch colour bar is provided below.
  • the colour bar is printed onto a substrate such as paper, card, fabric or any other suitable medium under the 'destination' printing conditions present at the printing unit 5.
  • the apparatus 1 causes the printed colour bar to be measured in the profile connection space to determine the colour of each patch.
  • the colour of the substrate is also measured, for example via the blank patch in the colour bar.
  • this stage comprises measuring the L*a*b* values of each patch.
  • the L*a*b* measurements can be made according to known techniques, for example by using a spectrophotometer 6 to read the L*a*b* values for each patch.
  • the spectrophotometer 6 may be comprised in the apparatus 1 and/or the printing unit 5 and is communicatively coupled to the controller 2 so that data can be exchanged between the two devices.
  • the spectrophotometer 6 may be installed in a paper outlet path of the printing unit 5 so that colour bars on sheets of paper moving along the outlet path can be routinely measured.
  • the outlet path may be separate to a main outlet path which is being used to output the results of the rest of the print job.
  • the substrate and/or the colourants being used at the printing unit 5 will not match those assumed in the source printing condition, in this case the ICC profile: 'ISO 12647-2, coated' .
  • combinations of printed colourants for example a particular CMY combination, may appear differently than would be the case if they were printed under the source printing condition.
  • the apparatus 1 is configured to create a CMYK to L*a*b* conversion profile for the printing unit 5. This constitutes a fifth stage of the process S5.
  • the conversion profile establishes a 'destination printing condition' for the printing unit 5 and can be created as an ICC profile.
  • the conversion profile comprises the relationships between the known CMYK colourant combinations in the printed patches and their measured L*a*b* values. For CMYK combinations which have not been printed in the colour bar and therefore for which there is no measured L*a*b* value, the conversion profile comprises a predicted CMYK to L*a*b* relationship.
  • the source printing condition for example 'ISO 12647-2, coated'
  • L*a*b* values for the colours of the base colourants e.g. L*a*b* values for C, M and Y inks or toner
  • the colourants in the printing unit 5 should be matched as closely as possible to these specified L*a*b* values.
  • the apparatus 1 is configured to convert the identified grey balance of the source printing condition (see Table A) to the destination printing condition of the printing unit 5.
  • the source printing condition, the conversion profile created for the printing unit 5 from measurement of the colour bar and the three L*a*b* grey balance values of the source printing condition are input by the controller 2 to a colour matching module 7 comprised in the apparatus 1.
  • a rendering intent, for example relative colorimetric or perceptual, for the source image is also input to the colour matching module 7 at this stage.
  • the rendering intent is selected based on the type of image which is to be printed, according to known techniques. The selection of rendering intent will decide whether the substrate colour or print contrast is used to determine the target L*a*b* grey balance value for the printing unit 5 (see below). Black point compensation can optionally be used.
  • the colour matching module 7 uses the inputted source printing condition 'ISO 12647-2, coated' , the conversion profile for the printing unit 5 and the rendering intent to adapt the L*a*b* grey balances of the source printing condition to the destination printing condition of the printing unit 5 using a known technique. Specifically, the colour matching module outputs sets of CMYK colour values which, if printed using the printing unit 5, would produce a visually neutral grey. These 'destination' CMYK values are calculated directly from the grey balance values of the source printing condition.
  • Table B l An example is shown in Table B l below, in which the L*a*b* values of the source grey balance given in Table A are adjusted to account for the differing aspects of the destination print condition.
  • Table B l Three CMYK 'destination' grey balance combinations are output by the colour matching module 7 - one for each of the source printing condition grey balances previously identified from the source profile: 'ISO 12647-2, coated' .
  • the apparatus 1 From the conversion profile established from reading the printed colour bar in the fourth step S4 described above, the apparatus 1 reads the L*a*b* values of the destination grey balance CMYK values. These 'destination' L*a*b* values are shown in the fourth column of Table B l .
  • the destination L*a*b values are stored in the memory 4.
  • L*a*b* values Due to limitations of the destination printing process, it may not be possible to achieve the source grey balance L*a*b* values under the destination printing condition. A reason for this may be that the L* values of the solid black colourant, or solid cyan, magenta and/or yellow colourants, in the source and destination printing conditions are different.
  • the L* value for solid black colourant in the source printing condition (ISO 12647-2, coated) is 16 whilst the L* value for solid black colourant in the destination printing condition is 33. Therefore, scaling is performed when making the conversion to ensure that detail in the image is not lost using known techniques.
  • the a* and b* values may be different between the source and destination printing conditions because of differences between the colours of the source and destination substrates which affect how the colour of the printed colourant is perceived. Therefore, as shown in Table B l , the target L*a*b* values for the destination condition may be different to the L*a*b* values in the source condition.
  • Another method of converting the identified grey balance of the source printing condition (see Table A) to the destination printing condition of the printing unit 5 uses the L* values of the solid cyan, solid magenta and solid yellow colourants of the source and destination printing conditions.
  • Scaling the L* values by this method prevents over saturation of the printed image, which can otherwise occur if the colourants of the destination printing condition are lighter and more saturated that the source printing condition.
  • the destination a* and b* values are calculated to be visually neutral on the printed material, based on the definition of grey balance previously discussed.
  • the apparatus 1 is configured to determine the L* value of a CMY overprint in the source printing condition (e.g. 'ISO 12647-2, coated' ) by reading directly from the source condition in the same manner as discussed previously.
  • the apparatus 1 is configured to determine the L* value of a CMY overprint in the destination printing condition by measuring the L* value of a printed CMY overprint patch in the printed colour bar in the manner previously described. Referring to Table B2 and figure 3, based on the measured L* value of the CMY overprint and the L* value of the unprinted destination substrate, the apparatus 1 is configured to generate curve data representing L* values of CMY tints in the destination printing condition.
  • the curve data represents values of L* across the range of CMY tints between the L* value of the measured CMY overprint patch and the L* value of the unprinted destination substrate, which is also measured from the colour bar.
  • the curve data between these range-end points is generated so as to identify a best-match between the destination L* values in the curve data and a set of desired L* values.
  • the desired destination L* values are usually not actually achievable, for example because of limited contrast available under the destination printing condition. If the desired L* values are not achievable under the destination print condition, the curve data is generated so as to identify a best-match with the desired L* values in the lighter regions of the image where the L* values are highest. Any discrepancy between the linear data and the curve data is concentrated in the darker regions of the image, where the L* values are lower. This is clearly illustrated in figure 3. The values are matched across as much of the tint range as possible. It will be noted that, in the specific example of Table B2 and figure 3, the L* value of the substrate assumed by the source condition is higher than the L* value of the destination substrate and therefore is not achievable. The maximum available L* value is that of the destination substrate.
  • the apparatus 1 is configured to read from the curve data the destination L* values which correspond to the L* values of the source grey balance and then to determine a* and b* values as previously discussed.
  • a further example of generated curve data is illustrated in figure 4, in which the destination L* value of the CMY overprint patch measured from the colour bar is 10 and the L* value of the CMY overprint patch read from the source condition is 20.
  • the apparatus 1 may be configured to convert the image CMYK values and grey balance of the source condition to an intermediate printing condition which is more closely matched to the destination printing condition.
  • the CMYK values of the image file may be converted to a standard newspaper printing condition which is more closely matched to the destination printing condition. These values then become the new 'source' values and can be used in the adjustment process described below.
  • An example for a standard newspaper printing condition is the ICC profile: ISO
  • the apparatus 1 is configured to determine adjustments which are necessary to achieve a colour match between the source and destination printing conditions. This allows the CMY and K values of the source image file to be adjusted so that, when printed at the printing unit 5, the colour of the image is optimal. A detailed explanation is given below.
  • the apparatus 1 is configured to read which tints of black (K) and combinations of non-black colourants (CMY) need to be printed under the destination printing condition to match the target L*a*b* values for the destination grey balance. This constitutes the sixth stage S6 of the process.
  • K tints of black
  • CMY non-black colourants
  • the apparatus 1 is configured to iterate through the tints of black colourant (K) in the source printing condition, 'ISO 12647-2, coated' or 'ISO Newspaper26v4' , to find the K tints which have an L* value most closely matching the L* of the identified target grey balances of the destination printing condition (see Table B l).
  • K black colourant
  • the apparatus 1 is configured to iterate through the combinations of non-black colourants (CMY) in the source printing condition, 'ISO 12647-2 coated' or 'ISO Newspaper26v4' , to find the CMY combinations which have L*a*b* values most closely matching the L*a*b* of the target grey balance of the destination print condition.
  • CMY non-black colourants
  • Table D An example of the differences between the CMYK values of the source and destination printing conditions is shown in Table D below. It will be appreciated that the majority of values in Table D are derived directly from Tables A and C discussed above. An extra line, corresponding to a source condition black colourant (K) tint percentage of 10 is also included for illustrative purposes.
  • the apparatus 1 is configured to establish a black colourant (K) adjustment curve which can be used to adjust all 'source' values of K for the image file to corresponding 'destination' K values that should be printed at the printing unit 5.
  • K black colourant
  • An example is shown in Figure 5.
  • the values of K are plotted against each other for the source and destination printing conditions.
  • the apparatus 1 is able to convert any value of K in the source image file to a value of K that should be printed at the printer 5, thereby maintaining a colour balance in the printed image.
  • a similar process is carried out for the tints of CMY.
  • the apparatus 1 is configured to establish an adjustment curve for each non-black colourant (CMY) which can be used to adjust all 'source' values of C, M and Y in the source printing condition to corresponding 'destination' C, M and Y values that should be printed at the printing unit 5. Examples are shown in Figures 6, 7 and 8. By reading across the curves, the apparatus 1 is able to convert any value of C, M or Y in the source image file to a value of C, M or Y that should be printed at the printer 5, thereby maintaining a colour balance in the printed image.
  • CMY non-black colourant
  • the colour bar can be printed at regular intervals, for example across the bottom of an A4 or A3 sized substrate, throughout a main print run so that the grey balance of the destination printing unit 5 is continually matched to the grey balance of the source printing condition.
  • variations in the colour of the colourants at the destination printing unit 5 can be measured during the print run and appropriate adjustments can be made to the printed CMYK values to maintain grey balance.
  • the method is not limited to the colours of the non-black colourants at the printing unit 5 being CMY. The method can be used whatever the non-black colourants of the printing unit 5, as long as the colourants can be combined to print a neutral grey.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Theoretical Computer Science (AREA)
  • Human Computer Interaction (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Facsimile Image Signal Circuits (AREA)
  • Color Image Communication Systems (AREA)

Abstract

La présente invention concerne un procédé pour la reproduction d'une image en couleurs comprenant l'identification d'un équilibre des gris d'un état d'impression de source d'un fichier d'images à imprimer, l'identification d'un état d'impression d'une unité d'impression à utiliser pour l'impression du fichier d'images, la conversion de l'équilibre des gris de l'état d'impression de source en un équilibre des gris de l'état d'impression de l'unité d'impression, l'établissement d'une différence entre l'équilibre des gris de l'état d'impression de source et l'équilibre des gris de l'état d'impression de l'unité d'impression et l'application de la différence établie aux valeurs de couleur dans le fichier d'images pour produire un ensemble de valeurs de couleurs à imprimer au niveau de l'unité d'impression. Le procédé peut être mis en œuvre au moyen d'un appareil qui est configuré à cet effet.
PCT/GB2012/051031 2011-05-20 2012-05-11 Appariement de couleurs WO2012160346A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1108513.1A GB2490965A (en) 2011-05-20 2011-05-20 Colour image reproduction using grey balance difference between source printing and current printer conditions
GB1108513.1 2011-05-20

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WO2012160346A8 WO2012160346A8 (fr) 2013-04-04

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CN106464774A (zh) * 2014-04-28 2017-02-22 惠普发展公司有限责任合伙企业 对信息进行处理以将至少一种不透明油墨用作处理着色剂
CN112073594A (zh) * 2019-05-25 2020-12-11 森大（深圳）技术有限公司 灰平衡调节方法、装置及计算机可读存储介质

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CN112040088B (zh) * 2020-09-08 2022-08-12 杭州电子科技大学温州研究院有限公司 一种用于打样的模拟设备特性文件的修正方法

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EP0851669A2 (fr) * 1996-12-26 1998-07-01 Fuji Photo Film Co., Ltd. Procédé de transformation de couleurs
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EP1536631A2 (fr) * 2003-11-26 2005-06-01 Hewlett-Packard Development Company, L.P. Réglage de gris neutre dans un profil couleur d'un système d'image

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EP0851669A2 (fr) * 1996-12-26 1998-07-01 Fuji Photo Film Co., Ltd. Procédé de transformation de couleurs
US20040190019A1 (en) * 2003-03-28 2004-09-30 Hong Li Methods, systems, and media to enhance image processing in a color reprographic system
US20050094170A1 (en) * 2003-10-30 2005-05-05 Konica Minolta Business Technologies, Inc. Image forming method and apparatus
EP1536631A2 (fr) * 2003-11-26 2005-06-01 Hewlett-Packard Development Company, L.P. Réglage de gris neutre dans un profil couleur d'un système d'image

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CN112073594A (zh) * 2019-05-25 2020-12-11 森大（深圳）技术有限公司 灰平衡调节方法、装置及计算机可读存储介质

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GB2490965A (en) 2012-11-21
GB201108513D0 (en) 2011-07-06

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