Applying VCGT to 3dLUT

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  • #5546

    V Tran
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    Hi Florian,

    I wanted to say thank you first for this magnificent works and your support for the community. It’s one of the most helpful project I’ve ever experienced. THANK YOU!

    After spending days of testing, reading the material (from the front page of DisplayCal, this forum and the previous forum on sourceforge.net. I couldn’t understand how this work.

    I have a few monitors that need to be calibrated through a 3dLUT (LG 34UM95, SmallHD 702 Bright, SmallHD 502) to Rec 709/BT 1886 with a i1Display Pro, going through Davinci Resolve 12.5. These monitor are not a part of the desktop. They are not connected directly to my graphic card (GTX 780Ti) but going through a UltraStudio Mini Monitor, which is essentially the same as a DeckLink PCIe card.

    Please correct me if I’m wrong but from the material, you mentioned to leave the “Apply Calibration (vcgt)” on for my situation. I realize since: “The “Resolve” preset is set up to not use iterative gray balance calibration, as normally it shouldn’t be needed.”, plus as you mention in your previous post on this forum, if set the Tone Curve = As Measured and the vcgt on, it will simply be linear at this case. Therefore it doesn’t matter if the Video Card Gamma Table is enable or not, they should both end up with the same result (Am I correct?).

    I’ve created two version of the 3DLUT, one with the VCGT on and one with it off. The “on” version give me a lot of weird artifacts such as banding, posterization. The color transition is very harsh and extreme. But with the setting “off”, it give me a nice result. (I did measure the Override minimum display update delay to 1200ms have the avg. delta e @ 0.37 and max at 3.7)

    Can you help me explain this? Also do you have any recommendation to my work flow? My objective is to have my monitor to display as accurate as possible.

    Thank you!

    Calibrite Display Pro HL on Amazon  
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    #5549

    Florian Höch
    Administrator
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    Hi,

    attach the profile and logs please (next to “Settings”, “Create compressed archive…”).

    [ thank you for the kind words! ]

    #5550

    V Tran
    Participant
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    Thank you for your support. Here are the compress of a few lastest tests that I did.

    Please let me know if you need me to provide anything else.

    Have a great day!

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    #5560

    Florian Höch
    Administrator
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    Thanks. The Ariel_LG_2017-01-16__09-19__.icc profile seems fine, all the others are botched in one way or another due to botched measurements (probably too low minimum display update delay, Resolve is unfortunately a lousy patch generator), so this is not related to applied calibration or not (linear will not make a difference anyway).

    #5569

    V Tran
    Participant
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    You ROCK Florian!

    So I did another 2 tests, I ditched Resolve and connect the LG 34UM95 directly to my video card. Changed the gamma from BT 1886 to 2.2 just to see and test and select a “Spectral: LCD White LED IPS” as a correction. I never had any issue with profiling the monitors using ICC but it’s very weird this time. There are some heavy banding toward the white part and color is wayy off. I’ve included the compress for you to see and a picture of how the monitor display magenta instead of grey. I must have done something wrong but so far I couldn’t come up with any solution.

    I’m trying my best to dig around the internet and learning about color management as much as possible since i find it extremely fascinating. I hope you don’t mind me asking a few stupid questions. As far as I know, except for ICC v4, ICC v2 only correct the gamma and the grey scale but not the gamut and that’s why 3dLUT is the preferable way. I read that Argyll doesn’t support v4 and checked the ICC on my computer, they are v2.2. But when I see my monitor shows magenta instead of grey and see DisplayCAL using the Auto-optimized test chart,  isn’t the ICC alter the color gamut of the monitor in some way too?  If not, is it right to say by applying a calibrated ICC v2 profile we won’t know if the color we are looking at is correct?

    THANK YOU so much for your time Florian!

    • This reply was modified 7 years, 2 months ago by V Tran.
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    #5594

    Florian Höch
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    There are some heavy banding toward the white part and color is wayy off.

    There’s something very wrong indeed, the measurements seem totally botched, so I am beginning to wonder if this is an instrument (hardware) failure. Do you have the ability to cross-check with the vendor software (e.g. i1 Profiler) and/or on another computer?

    As far as I know, except for ICC v4, ICC v2 only correct the gamma and the grey scale but not the gamut

    That’s incorrect, there’s no such limitation in ICCv2. From a user’s perspective, there is no difference in the way that ICCv2 and ICCv4 profiles operate.

    The difference between ICC device profiles and a 3D LUT is that the latter describes a “baked” color transform, while ICC device profiles are linked to create a color transform on the fly. I.e.

    Abstract color transform:
    (source) colorspace -> (source) rendering intent -> PCS -> (destination) rendering intent -> (destination) colorspace

    Example color transform involving two ICC device profiles:
    sRGB -> relative colorimetric -> PCS -> relative colorimetric -> display profile

    The above transform can be baked into a single file ICC device link profile or 3D LUT that, when applied, produces the same result.

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