Gamma doesn’t match hardware calibration

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  • #658

    jmend SourceForge
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    I’m trying to create a 3d Lut for my Dreamcolor z24x using Davinci Resolve, following the instructions posted here. I first calibrated the monitor using their software with the i1 display pro OEM, to Rec709 2.2 gamma. I can verify this calibration which gives me this result:
    Imgur

    Yet, when I attempt to profile it to BT1886 with dispcalgui to create the LUT and go to verify it, I get this as my gamma:
    Imgur

    So I tried to profile it to Rec709 2.2 gamma, thinking it would make a difference and got this:
    Imgur

    I’m at a loss as to what is causing this, since all the other sections are improved with a 65^3 lut. Obviously the display can be calibrated and verified, so it must be something I’m doing wrong. Any ideas?

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    #659

    Florian Höch
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    Hi, can you attach the full HTML reports? Thanks.

    #664

    anonymous SourceForge
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    well, not sure if I should be posting this here but since it is a Resolve topic I might as well..

    I am running Resolve Lite 11 and am following the same instructions; only I cannot select the Calman tab under the monitor calibration tab under color in Resolve.. I thought the Lite version of Resolve supports calibration? Have been looking for a solution but I can’t find anything..

    #666

    jmend SourceForge
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    I was having issues with adding attachments, so here are downloadable links from my dropbox. You won’t have to “save as”.

    Measurement Report 3.0.1.0 — Resolve — 2015-06-03 00-44.html

    Measurement Report 3.0.1.0 — Resolve — 2015-06-03 00-46.html

    Measurement Report 3.0.1.0 — Resolve — 2015-06-03 01-12.html

    #665

    Florian Höch
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    #663

    anonymous SourceForge
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    Hey Florian, just wondering if you think I should go with the HP calibration for the moment? I don’t particularly like it since it tends to give me a more magenta-ish look on upload, but I can work around it if you think my gamma issue may pose a problem. Thanks.

    #660

    jmend SourceForge
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    Hey Florian, just wondering if you think I should go with the HP Cal for now, or not be too concerned with the gamma issue?

    #661

    Florian Höch
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    I would try using the “LCD RG Phosphor” spectral correction (re-do the profile & 3D LUT) and see if that improves things.

    #662

    jmend SourceForge
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    Just did that, and while it did fix the gamma issue, the rest of the cal went downhill. What has worked, although I’m not sure if it is the reason, was to:

    recalibrate the monitor using the Dreamcolor calibration solution software. Then run the calibration using dispcal, but set the calibration tone curve to as measured instead of BT1886 or Rec709.

    It’s the only thing I’ve done different, and all my measurements now fall below the recommended delta and my gamma range is below .5 on all settings (Rec709 2.2, 2.4, and BT1886).

    Thanks for all your time and effort. I know it’s free software, but I’ll donate first job I book.

    #667

    anonymous SourceForge
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    You need to use “RG Phosphor” for Measurement report process, so all 3 attached files are not valid.
    You have a GB-LED so you MUST apply a proper spectral correction (RG Phosphor) for EACH measurement you do with the i1DisplayPro and those kind of displays

    #668

    jmend SourceForge
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    I had posted that I tried to calibrate and then measure the display using that correction, but it did not solve the issue. Instead, made it worse.

    In my OP I said I have the OEM i1displaypro, which is the Dreamcolor Calibration Solution version. This comes with custom filters for the Dreamcolor display, so no correction should be needed for this probe, since it is made specifically for this display.

    The ONLY thing that worked, was to clear out the calibration. If I calibrate with a set tone curve, I get the same erroneous results with gamma. I should have also said I’m feeding the monitor through a BM mini monitor, and not the video card. So the issue may have been that.

    Here are my latest cal reports in case I’m mistaken.

    Attachments:
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    #670

    anonymous SourceForge
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    You are wrong. OEM version for Z24x is just a way to get money from you, cause it is the only way to internally calibrate it, which is a shame.
    Z24x uses the sem AH-IPS panel from LG as U2413, so RG_phosphor correction should be applied for all CCSS compatible devices (i1d3, Spyder4&5 and color munki display). i1DisplayPro DOES NOT come with “firmware” tweaks, like from Widegamut versions of i1d2 or Spyder3 did. It’s firmware stores actual spectral sensibility of device, that’s why you can use CCSS/EDR corrections and you don need to match a specific colorimeter to a specific display.
    The only way an i1d3 measures “perfectly” a GB-LED is to have “perfect” sensibility curves in its filters. So a “NONE” spectral correction in your reports means that they are always wrong measurements

    So if you perform a profile validation using a generic profile, and you set “tonal curve” =”unmodified”, and results are wrong… your hardware calibration is WRONG.

    You are doing the opposite way, let’s tweak everything until DispcalGUI says “you’re OK”, which is a nonsense. It’s like cheating in Solitaire.

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    #671

    Florian Höch
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    i1DisplayPro DOES NOT come with “firmware” tweaks, like from Widegamut versions of i1d2 or Spyder3 did. It’s firmware stores actual spectral sensibility of device, that’s why you can use CCSS/EDR corrections and you don need to match a specific colorimeter to a specific display.

    Yes.

    So if you perform a profile validation using a generic profile, and you set “tonal curve” =”unmodified”, and results are wrong… your hardware calibration is WRONG.

    No, the underlying problem of the issue reported in the first post is not the calibration/profile/3D LUT, but a bug in the measurement report code that I’ll have to fix. Basically, all verifications run through a device link that alters device white (e.g. when the display is not being adjusted to match the target whitepoint, and absolute colorimetric intent is used for the 3D LUT) will be erroneous in the current version of DCG. The way to work around the issue until the fix is available is to adjust the display whitepoint to match the target whitepoint, and/or use relative colorimetric intent when creating the 3D LUT.

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