How to verify my BT2020 2.4 gamma 3dlut?

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This topic contains 14 replies, has 3 voices, and was last updated by  Florian Höch (@fhoech) 1 year, 8 months ago.

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  • #10750

    stef22 (@stef22)
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    Hello Florian,

    I have profiled my JVC projector, and the report says it covers 99.7% of the DCI-P3 colorspace with an average deltaE of 0.13 max 1.71. I have then created a 3dlut using BT2020 as the source and a gamma of 2.4 relative 100 black output offset. I would like generate a report telling me how accurate the result is.  My plan is tu use madvr hdr to sdr pixel shader conversion, which should be feeding the 3dlut with a BT2020 gamma 2.2 signal from what I’ve read.

    I am unable to get a verification report that makes any sense. On the verification tab, what settings should I use? I am at loss here…

    • This topic was modified 1 year, 9 months ago by  stef22.
    • This topic was modified 1 year, 9 months ago by  stef22.
    #10753

    stef22 (@stef22)
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    By the way, I have tried generating verification report using the pre -selected info from the verification tab (I have changed nothing there):

    simulation profile: bt.2020, use simulation profile as display profile and enable 3d lut both clicked, gamma custom 2.4

    The resulting report gives me an average deltaE of 4.35, maximum 9.53…

    #10764

    Florian Höch (@fhoech)
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    If your display doesn’t actually cover Rec. 2020 (or just a small part thereof), which is basically true for all available displays (except some prototype laser projectors), then a lot of colors will simply clip, thus explaining the high delta E.

    #10766

    stef22 (@stef22)
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    Thank you, I can understand that!

    Since my display can do 99.7% of the DCI P3 colorspace, how can I test for that? please, could you tell me the exact settings I must enter on th verification tab?

    #10768

    Florian Höch (@fhoech)
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    Set simulation profile to DCI P3, then disable “Use simulation profile as target” (and 3D LUT).

    #10786

    RamdomUser (@ramdomuser)
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    A related issue, sorry for not opening a separate thread:

    When I select madvr as display and go to verification tab, simulation profile enabled + enable LUT3D, “Measurement report…” is disabled.
    Why? It happens with or without madTPG started from before (LUT3D ON, GPU LUT OFF).

    I do not want to use “3dlut tab” but instead generate each 3dlut with the standalone “DisplayCAL-3DLUT-maker.exe” to a folder of my choose… or even ArgyllCMS command line, or other programs, then setup madVR and asign each LUT3D entry from files in that folder. Then measure with DisplayCAL how those LUT3D behave.

    I do not see the reason why it’s disabled since DisplayCAL/ArgyllCMS should be “clients” of madTPG, just send the patches and read them, no matter the source of madVR’s LUT3D.

    #10799

    Florian Höch (@fhoech)
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    When I select madvr as display and go to verification tab, simulation profile enabled + enable LUT3D, “Measurement report…” is disabled.

    Sorry, cannot reproduce this. Is a profile selected under “Settings”? This is required for any tone curve selection other than “Unchanged” because of the need to know the display black level (which is read from the display profile).

    #10800

    RamdomUser (@ramdomuser)
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    When I select madvr as display and go to verification tab, simulation profile enabled + enable LUT3D, “Measurement report…” is disabled.

    Sorry, cannot reproduce this. Is a profile selected under “Settings”? This is required for any tone curve selection other than “Unchanged” because of the need to know the display black level (which is read from the display profile).

    Thank you. Problem solved.

    #10809

    stef22 (@stef22)
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    Set simulation profile to DCI P3, then disable “Use simulation profile as target” (and 3D LUT).

    Hi again! I am having a hard time uncerstanding how to verify my 3dlut…

    I have profiled my display and it covers 99.7% of DCI-P3 (attached file 001) with good deltaE I think. I have adjusted my white point to D6500K using my display’s controls to obtain that.

    Then, I have created a 3dlut from it with BT2020 as the source and gamma 2.4  as the tone curve (attached file 002)

    Then I used the setting you suggested to verify my profile without the 3dlut enabled (attached file 003)

    And I got the following report (attached file 004)…it looks good to me! (though I dont know why the gamma changed to 2.6 by itself…)

    Then, I try to verify the effect of my 3dlut by clicking  use simulation profile as display profile and also enable 3dlut (attached file 005)

    But I get the following report (attached file 006) that does not look so good 🙁

    The report looks wrong…why does it say display profile whitepoint 6320K on my report with the 3dlut enabled? where does that number come from?

    I believe I shoud get quite good results with the 3dlut enabled, better results than without it? I believe my 3dlut is correctly designed, but the report is wrong. Can you help me understand it and how to generate a valid report?

    Thanks a million times!

    • This reply was modified 1 year, 8 months ago by  stef22.
    • This reply was modified 1 year, 8 months ago by  stef22.
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    #10814

    stef22 (@stef22)
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    Here are the files 005 and 006…

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    #10830

    Florian Höch (@fhoech)
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    why does it say display profile whitepoint 6320K on my report

    DCI-P3 has a non-D65 whitepoint (not close to daylight or blackbody locus), x 0.314 y 0.351, as shown on the report.

    I try to verify the effect of my 3dlut by clicking use simulation profile as display profile and also enable 3dlut

    You cannot use your 3D LUT to verify against DCI-P3 because your 3D LUT was created for BT.2020.

    #10842

    stef22 (@stef22)
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    You cannot use your 3D LUT to verify against DCI-P3 because your 3D LUT was created for BT.2020.

    Oh, Ok! I did not know there two DCI-P3 white points, one for cinema and one for D65…

    1- Now, going one step back, If I run a verification report of my 3D LUT (created for a BT.2020 source), every color from the test chart that is within the colorspace my projector can reproduce (99.7% of the DCI-P3 colorspace) should yield good deltaE, right? While every color outside of that will show larg(er) deltaEs, right?

    2- Second, my grayscale should give me better results than what I get without the 3dlut enabled?  I attach again my results without the 3dlut. From what I understand, colors with high deltaEs (colors that are probably within the DCI-P3 range) will not improve much, but grayscale and colors with already good deltaEs should either improve or at least remain the same?

    Thanks again for your time!

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    #10844

    Florian Höch (@fhoech)
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    Yes.

    #10855

    stef22 (@stef22)
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    Thank you again, I am almost there!

    Is there a test chart that I can use to verify the accuracy of my BT2020 3dlut that would only test for colors within the DCI-P3 colorspace … and if not, maybe only test colors within rec709 colorspace?  I would like to avoid testing for colors that are clearly outside of what my projector can display to get a useful report!

    • This reply was modified 1 year, 8 months ago by  stef22.
    #10868

    Florian Höch (@fhoech)
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    Is there a test chart that I can use to verify the accuracy of my BT2020 3dlut that would only test for colors within the DCI-P3 colorspace

    No. You could use the ArgyllCMS commandline tools to create such a chart.

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