Off-White Point calibration?

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  • #29651

    pyron
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    As it happens with blacks, pure white sometimes shows a bigger color balance delta than off-white patches, turning the calibration process for white point more harming on the overall picture.

    For instance, the next graph shows a display with perfect white point calibration, but everything else is very bad.

    If instead of calibrating to white we calibrate to say 90% white, the average delta for grey balance would be lowered, making it easier for the following characterization step (which would also fix the white point alongside).

    Is this a fair reasoning or something that could be implemented?

    #29655

    Vincent
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    It looks that no calibration was loaded during validation, like if you used sRGB profile as display profile in simulation. Do not use simulations while validating to check if this is was your issue (User misconfiguration).

    It may be caused by other issue, but without data is a  good guess.

    #29656

    pyron
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    No sorry, this is not an issue I have, I could very well just painted a graph.

    It’s more about the theory of white point calibration and the harm it can inflict in grey balance.

    For example, when calibrating a TV display I often have to tune the R, G, B sliders in such way that white point calibration is achieved but everything else (grey tones) are a complete mess. For these circumstances I am calibrating to off-white point, but I don’t see any body discuss this issue around.

    #29665

    Vincent
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    No sorry, this is not an issue I have, I could very well just painted a graph.

    It’s more about the theory of white point calibration and the harm it can inflict in grey balance.

    For example, when calibrating a TV display I often have to tune the R, G, B sliders in such way that white point calibration is achieved but everything else (grey tones) are a complete mess. For these circumstances I am calibrating to off-white point, but I don’t see any body discuss this issue around.

    Grey is corrected in GPU, if you do nothing grey is uncorrected. To test your theory you need to checl a*b* values relative to native white. Without that it’s nothing.

    #29672

    pyron
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    Grey is corrected in GPU, if you do nothing grey is uncorrected. To test your theory you need to checl a*b* values relative to native white. Without that it’s nothing.

    Do you know what the calibration step is for? because it looks as if you are not aware. Correcting a delta of 12 or more is not the same as correcting a delta of 3. Specially on TV where you don’t have GPUs to correct anything.

    • This reply was modified 1 month ago by pyron.
    #29674

    Vincent
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    Grey is corrected in GPU, if you do nothing grey is uncorrected. To test your theory you need to checl a*b* values relative to native white. Without that it’s nothing.

    Do you know what the calibration step is for? because it looks as if you are not aware.

    More than you, no doubts about that

    Correcting a delta of 12 or more is not the same as correcting a delta of 3. Specially on TV where you don’t have GPUs to correct anything.

    If TV has no n-point grayscale adjust… you can do nothing. It’s as bad as it is unless you plug it to a computer for playing video content with GPU and access to GPU LUTs (which invalidates raspberry pi as computer suitable for that task).

    #29676

    pyron
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    Grey is corrected in GPU, if you do nothing grey is uncorrected. To test your theory you need to checl a*b* values relative to native white. Without that it’s nothing.

    Do you know what the calibration step is for? because it looks as if you are not aware.

    More than you, no doubts about that

    Then polish off your communication skills because you just show ignorance. Chime in back when you have something juicy to add because so far you just produce noise.

    #29678

    Vincent
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    The only ignorant here is you, because you try to do things that your display does not allow to do (if it has no n-grey point adjustment) unless you use an external device (a GPU with access to its 1D LUTs).

    It’s difficult that you’ll be able to do something if you do not know the capabilities of your devices (for being an ignorant).

    • This reply was modified 1 month ago by Vincent.
    #29681

    pyron
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    you’re still not getting the point. What I’m saying is that calibration should make things easier for profiling, not making a mess at the cost of white point and then let the GPU fix the mess. The TV example was a corner case scenario where a disaster calibration can’t be fixed with GPU LUTs.

    #29684

    Vincent
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    you’re still not getting the point. What I’m saying is that calibration should make things easier for profiling, not making a mess at the cost of white point and then let the GPU fix the mess. The TV example was a corner case scenario where a disaster calibration can’t be fixed with GPU LUTs.

    Again, it’s your TV or monitor fault if it has not a way to fix grey internally. You can do nothing about it… well, you can plug it to a GPU as explained previously.

    Also that behavior you describe is limited to your devices, others do not behave that way.
    Also all those issues may be caused by user’s fault, messing with controls that he does not know, like those monitors with RGB Gain 50/100 by default where channel clipping can happen (vs RGB gain 100/100 by default)

    If your target white falls too off from native white you can try closest daylight white. It will look white (usually cool-blue but “white”, close to daylight or planckian loci). Uncalibrated screen report shows that value for you.

    • This reply was modified 1 month ago by Vincent.
    • This reply was modified 1 month ago by Vincent.
    #29716

    Wire
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    Hi Pyron, without a doubt Vincent is the most informed and active contributor on this site…  He may be feeling fatigue at certain questions / dialogs which are poorly informed as to basics of displays…

    Your question was, if I understand you,  Can DisplayCal be adjusted to help you when in your case where your display has a wild difference in peak white temperature as compared to a relatively uniform gray?

    The answer will be no, because that’s a symptom of a serious problem in display. It is not normal behavior.

    At least two common display controls can be mis-set to cause your situation: “contrast” and “gain/bias”. Basically these controls are holdovers from days of CRT where amplifiers are used to shape beam currents with characteristic responses to set peak white and RGB balance. LCD (matrix) displays have a complete different principle of operation, but the display UI designer tries to emulate CRT behavior, but because of tech limits the behavior can be iwacky. For example ir’s often the case that at some mid-point in the control range, say 75, a contrast control may “over drive” (so to speak) the LCD apertures and cause response clipping.  The “gain” controls may do same for each of RGB. Setting gain of 50 is sometimes the max, and beyond causes clipping or non linear behavior across other channels. Sometimes pictures modes and these controls interact in bogus ways. For example, maybe the set has a presentation mode that goes for highest brightness at expense of linear response (common in projectors). In your case I have no way to know, but these situations are not uncommon.

    There’s a difference between calibrating and profiling a normal system response and trying to overcome a system limit or defect. DCal developers can fix problems, only align normally functional displays.  What you are describing is a problem.

    So you have only option of reviewing controls to bring white / gray temp into normal alignment. From  there a GPU can further refine  and smooth response to higher precision, but it cannot account for clipping that causes the vast delta you report between peak white and gray,

    And when you have reviewed basics of calibration and can speak to the normal behavior of your gear, you will find Vincent to be a super well-informed and helpful resource.

    /wire

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