Linear profile

[Radiohead]

I would like a linear profile in both the tone response curves and in the calibration curves on Mac OSX.

This is because I have a CRT projector that I can calibrate and that has its own gamma response.

The option reset video card gamma table is not available it seems and I could not find a default profile with linear gamma.

Am I understanding things wrong? Perhaps I always need my Mac to do some kind of correction to the gamma? That does not make sense to me and makes me loose digital resolution perhaps resulting in color banding. I would like my Mac to do nothing to the material for optimal resolution right?

Thanks.

[Vincent]

I would like a linear profile in both the tone response curves and in the calibration curves on Mac OSX.

This is because I have a CRT projector that I can calibrate and that has its own gamma response.

I understand that you want linear calibration = no calibration in GPU since you say that you can change projector grey response internally. But, why do you want a linear (“gamma 1.0”) TRC  in profile? I see no point doing that for common uses, maybe I’m missing something.

If you want to avoid that macOS makes some changes in UI, use:

-all calibration settings to native/as measured, profile type to default values (to avoid macOS UI issues), then it will profile your projector without applying GPU calibration. Your projector should be calibrated in advance. Button should change name to “profile only” on something like that when you choose as calibration settings = native.
This way you get no GPU calibration and a simple profile with actual CRT primaries.

or

-if you do not care about/you do not want gamut/colorspace correction, then choose one of the default profiles that matches better your projector (or make a synthetic one with DisplayCAL tool), then make your proyector behave like that with its vendor calibration tool.

[Radiohead]

Ok I managed to make a profile with a linear response in the GPU so the GPU is out of my equation.

I also played with the create synthetic profile tool and when I selected Tone Curve ‘custom’, and gamma = 1 I got a really extreem tonal response curve  so obvious I am not understanding this 100%. 🙂 When I choos gamma = 2.2 I get a somewhat linear tonal response curve with the small bump in low light regions that seems much better.

Let me rephrase my problem. I would like my Mac to do the same thing to the video material as my Oppo blu-ray player and I assume the Oppo does nothing. Am I misunderstanding something here? Perhaps the Oppo is making a gamma 2.2 from the video material too?

Thanks!

[Vincent]

There are two stages

– make my device behave like “…” a.k.a. “calibration”
When using common GPU calibration this is limited to white point & grey, no gamut correction so far.
Your projector should do something similar internally as you said that you can change its gamma without a computer.

-measure how my device behaves and store that information a.k.a. “profiling”
When you made synth profile it is likely that you store no calibration for GPU but store the gamma values you chose. Instead of measuring like usual profiling, you made it “synthetic”.
If you say to macOS via display synth profile “that display has gamma 1.0” you are forcing color aware programs to “undo it” to usual gamma 2.2 (or sRGB or whatever it was meant to be). Thats why I wrote:

But, why do you want a linear (“gamma 1.0”) TRC in profile? I see no point doing that for common uses, maybe I’m missing something.

If you want that color managed/aware apps do nothing when using your proyector, just assign usual content colospace profile to that display. For example a synth sRGB profile or a synth Rec709 profile with gamma 2.2 or 2.4.

If you want your mac screen to behave like that projector, measure projector whitepoint then put it as calibration target. Leave other profiling options as default because od macOS issues with profiles. This will fix white but not colospace differences unless you use some kind of color aware player.
IDNK too much about video players for macOS: mpc (GNU) and system default (Apple). mpc should be color aware although its configuration does not look user friendly.
IDNK if you can use some kind of software LUT3D in mpc to “exactly match” proyector response if your mac display was capable of covering the whole proyector colorspace.

• This reply was modified 4 years, 5 months ago by Vincent.

[Radiohead]

Thanks again this was very helpfull. I created a few synthetic profiles to test with sRGB, 2.2 and 2.4 gamma.

One small question remains. Do you know if Blu-ray video is encoded with the sRGB 2.2 or a straight 2.2 or even a straight 2.4 gamma?  That keeps me thinking.

I use my Mac with hdmi to a CRT projector with a hdmi input card. The hdmi card lets me chose some gamma settings.

[Vincent]

Don’t worry about how it is encoded, worry about how its contents are meant to be viewed.

Rec709 says little about that 2nd subject. Usually you can use for viewing:
-2.4 (or 2.4 until your limited contrasts display cannot go darker so gamma starts to be lower in darker greys to keep distance between each grey tone)
-Rec1886 in displays with VERY HIGH contrast. 1000:1 static contrast ratio is not high (even 2k may not be considered that). Rec1886 should be close to 2.4 on a high contrast display. If you use it on a low contrast display, gamma will roll to lower values sooner that in 1st example (2.4 power law “as long as you can”).
-2.2, but video content is usually made with 2.4 in mind with a few 2.2 web exceptions that not all people agree on.

IDNK your vieweing conditions for projector, or for your mac.
Internet content is usually menat to be displayen without color management on sRGB-like displays and near 2.2/sRGB gamma. So people usually calibrate their displays to this 2.2 target (which is usually close to display native gamma response). Then you can use a color managed video player to display movies or blurays as “2.4” and keep the usual 2.2 gamma in OS desktop.

Advice:
-Keep usual computer gamma for your mac display (2.2-like).
-Take a look on those color managed videoplayers for macOS and see how to configure them to display movies as if they were shown in a 2.4 display. “mpv” vidoe player should be able to do that in the same way we can do it in Windows with mpv or with madVR.

[Radiohead]

Rec1886 seems to work very good with my projector (CRT should be 100.000-30.000 static contrast). I found a setting in VLC player that lets me chose this gamma for output. I think VLC player is not using the profile so I am trying MPV as alternative.

One more question. When I make a synthetic profile I do not want it to correct the contrast of the video material. Chosing white level 120, black level 0 hopefully does nothing? Not sure if I understand those  settings.

Thanks!

[Radiohead]

My HT is very dark by the way, justifying rec 1886.

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