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Thread: Calibrations curve

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    Junior Member urbis72 is on a distinguished road
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    Red face Calibrations curve

    I have to make a calibration curve offset by one medium printer house in Europe for plate.

    I have a device xrite exact advanced.
    To calculate the correct TVI, first I need to know how much the operator of the machine have to keep strongly color densitometer value. (examples 1.2 for cyan)

    So I imagined that making this form,





    and measure the print without polarization filter.

    So on a sheet of paper, looking for the true value LAB for certain paper of each color.



    When he measured / find correct LAB for example Cyan colors, then he measured density at that point and make new print with measured density

    Do I start ok or?

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    PRC Member ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard's Avatar
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    Hello urbis72,

    Yes, in general, you are in the right direction. The best suited SID value should have the lowest dE value in comparison with the target L*a*b*.
    You also have to take into account the difference between wet and dry measurements. Typically pressman gets wet measurements, while a client gets dry measurements. So, you should to find the lowest dE value for the dry measurements, while a pressman should get the density target for the wet measurements.
    As soon as SID is under your control you have to take care about the following (in short):
    • plate production quality, because it impacts on print variations,
    • short-term variations within printing sheet (along and accros of printing sheet), because variations impact on the quality of measurements and overall quality.
    Ideally, you should not make any corrections to a process (for example, press calibration and/or profiling) until you didn't take special causes of variations under control.
    Last edited by ColorWizard; 08-07-2015 at 11:53 AM.
    Cheers,
    CW

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    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by urbis72 View Post
    I have to make a calibration curve offset by one medium printer house in Europe for plate.

    I have a device xrite exact advanced.
    To calculate the correct TVI, first I need to know how much the operator of the machine have to keep strongly color densitometer value. (examples 1.2 for cyan)

    So I imagined that making this form,





    and measure the print without polarization filter.

    So on a sheet of paper, looking for the true value LAB for certain paper of each color.



    When he measured / find correct LAB for example Cyan colors, then he measured density at that point and make new print with measured density

    Do I start ok or?
    if you are talking about standardized target lab values you also have to take the paper white point into account. without the correct paper stock you wont meet standard values!

    and as colorwizard already said: first you have to measure all wet density values and find the matching lab value after 24 hours of drying time.

    and the sequence of printing inks is also important for getting standard results.

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  6. #4
    Junior Member urbis72 is on a distinguished road
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    Thanks for your reply,

    Quote Originally Posted by ColorWizard View Post
    Hello urbis72,

    Yes, in general, you are in the right direction. The best suited SID value should have the lowest dE value in comparison with the target L*a*b*.
    I do not understand what you wanted to say, do not understand the meaning of SID


    Quote Originally Posted by ColorWizard View Post
    You also have to take into account the difference between wet and dry measurements. Typically pressman gets wet measurements, while a client gets dry measurements. So, you should to find the lowest dE value for the dry measurements, while a pressman should get the density target for the wet measurements.

    First pressman make an print.

    What is best density pressman makes the first print, with the usual settings to print or otherwise?

    First make a measurement with polarization filter to get the closest LAB values on the wet print.

    When I get an approximate value of dE, I have to wait for print dried and then again to make a measurement of dry marks without polarization filter, the value will go down, so how I know which much we need to increase the density of wet print?

    examples
    dE F39
    Ref L Ref a Ref b
    55.00 -37.00 -50.00

    and I have for dry print

    Ref L Ref a Ref b
    45.00 -17.00 -40.00



    I do not understand this part, I had to find the lowest value dE dry print.


    Quote Originally Posted by ColorWizard View Post
    As soon as SID is under your control you have to take care about the following (in short):
    • plate production quality, because it impacts on print variations,
    • short-term variations within printing sheet (along and accros of printing sheet), because variations impact on the quality of measurements and overall quality.
    Ideally, you should not make any corrections to a process (for example, press calibration and/or profiling) until you didn't take special causes of variations under control.
    OK, I understand this part :)

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    Junior Member urbis72 is on a distinguished road
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    Quote Originally Posted by spider View Post
    if you are talking about standardized target lab values you also have to take the paper white point into account. without the correct paper stock you wont meet standard values!

    and as colorwizard already said: first you have to measure all wet density values and find the matching lab value after 24 hours of drying time.

    and the sequence of printing inks is also important for getting standard results.

    and the sequence of printing inks is also important for getting standard results

    Are you under this thought with all the other colors MYK?
    is there any other quick solution with minimal equipment to take it all make measurements?

  8. #6
    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by urbis72 View Post
    and the sequence of printing inks is also important for getting standard results

    Are you under this thought with all the other colors MYK?
    is there any other quick solution with minimal equipment to take it all make measurements?
    standardization is not only about tvi curves!

    you have to measure the tvi spread / gray balance too.

    target lab values are not only defined for cmyk but for complementary colors too.

    if color sequence and color trapping is not correct inside the printing press your measurements will fail!

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    Junior Member urbis72 is on a distinguished road
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    Quote Originally Posted by spider View Post
    standardization is not only about tvi curves!

    you have to measure the tvi spread / gray balance too.

    target lab values are not only defined for cmyk but for complementary colors too.

    if color sequence and color trapping is not correct inside the printing press your measurements will fail!

    OK, you wanted to say that we need more measured gray balance as well as RGB, but I do not understand why is it important?

    Or how to explain it, I do not know when I get the results, what to do if it is too dark / too bright, or the increased value / decrease

  10. #8
    Junior Member shampa will become famous soon enough
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    Once you have hit the target solid C/M/Y values then you should check the R/G/B overprints are close to the ISO standard values. Assuming you are printing with a standard KCMY or CMYK order they should be close. If not then you have an issue with your press, chemistry or ink that you should investigate before going further.

    The next step is to measure the tone curves and enter into the rip as your press curve. At this point you should be hitting the ISO standard and you can either stop here or keep going and fine tune your grey balance. Note that this will most likely take you slightly away from the target ISO TVI curves, but should still be within tolerance.

    Even though the grey balance will take you slightly away from the ISO ideal, it makes it easier to get consitent colour on press and gives a better visual match than just a straight application of the ISO standard does.

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  12. #9
    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by urbis72 View Post
    OK, you wanted to say that we need more measured gray balance as well as RGB, but I do not understand why is it important?

    Or how to explain it, I do not know when I get the results, what to do if it is too dark / too bright, or the increased value / decrease
    you dont understand why this is important?

    very easy! you dont only print individual cmyk colors. what about all mixed colors made up of two or three primary colors? if you want to be able to print the visual result of a standard proof you have to meet ALL aspects of the ISO standard! not only tvi and lab of cmyk.

    first you have to make sure the printing machine is in perfect condition and is printing
    consistent results. otherwise you can stop here.

    if rgb lab values are not ok there is something wrong with printing machine / printing order or the ink. there is nothing YOU can do to improve this.

    another important aspect you have to check is that you have the same tone values at every position of the plate and the press sheet. this is not self-evident! especially if the printing press is worn out you will struggle here.
    Last edited by spider; 08-09-2015 at 12:53 AM.

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  14. #10
    PRC Member ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard is a glorious beacon of light ColorWizard's Avatar
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    I agreed with spider, you have to be sure that the printing machine is in perfect condition and is printing consistent results.
    I repeat, I don't see any reason to correct the behavior of the production process before you established the quality control on all stages of this process.
    You didn't say if you can predict the print result, but I can suppose that you can't. It seems to me, that you don't know the tolerances in which your process is able to produce the result. Thus, the production process, most likely, is not under your control.
    So, I would suggest leave the idea of the linearization, but concentrate on the implementation of the process quality control.
    Very briefly and roughly:
    1. Find and eliminate all the special causes of the process variation (the most complex and costly part) - short-term and long-term variations of the printing process.
    2. Test if the process is capable to produce the result inside the given tolerances (ISO 12647-2?) - process capability index.
    3. Calibrate and, if necessary, profile the printing process (color conversion, as the stage of the production process, should be under your control too).

    As you can see, I believe, that the calibration/linearization is one of the final tasks you have to perform.
    Cheers,
    CW

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  17. #11
    Junior Member urbis72 is on a distinguished road
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    Machines are functioning properly for printing.
    I do not understand a part, when I get the result, to know if something get less or more LAB, RGB, what to do, reduce or turn up the color

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    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by urbis72 View Post
    Machines are functioning properly for printing.
    I do not understand a part, when I get the result, to know if something get less or more LAB, RGB, what to do, reduce or turn up the color
    first you have to understand lab colour space.

    if you keep the three axis of the colour space in mind you will see easily if you have to print more or less density.

    but if you print your suggested test triangle you can also measure which ink zone meets the best lab value. if you want to match rgb too, obviously you have to print other test strips too.

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  20. #13
    Junior Member urbis72 is on a distinguished road
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    Quote Originally Posted by spider View Post
    first you have to understand lab colour space.

    if you keep the three axis of the colour space in mind you will see easily if you have to print more or less density.

    but if you print your suggested test triangle you can also measure which ink zone meets the best lab value. if you want to match rgb too, obviously you have to print other test strips too.
    That's right Spider
    And how best to understand axis colour space?

    First, I'll print test triangle to see with whom the density need to print real test, I'm interested in whether the different way?

    The only thing that bothers me with wet and dry measurements, to calculate properly

  21. #14
    Junior Member shampa will become famous soon enough
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    Quote Originally Posted by urbis72 View Post
    The only thing that bothers me with wet and dry measurements, to calculate properly
    You cannot calculate dry from wet or vice-versa, as there are unknown variables involved. You need to take two sets of measurements, one wet (using the instrument that you will be using on press for day to day process control) then one measuring the same spots when dry (using an accurate spectrometer). Preferably the wet measurements should be UV-cut, polarizing filter and black backing, whereas dry measurements should be M1, white backing.

    Instead of your triangle, use discreet steps and include a measuring patch inline with the step to make it easy to make repeatable measurements. You can also include step wedges inline to measure your press curve from the same sheet.

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  23. #15
    Junior Member urbis72 is on a distinguished road
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    Me again :)

    With Fogra we took FOGRA39.txt, and there we read values for CMYK in the LAB, as you say that we need to measure the RGB values, where they can read the RGB values in the LAB?


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