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Display Calibration Light Illusion Forums / Display Calibration /

What Gamma Curve to use?

Author aprilliasky
Mono
#1 | Posted: 1 May 2013 22:24 | Edited by: aprilliasky 
Hi!
For calibration I was wondering what gamma to use. My target is Rec. 709. As far as I know this standard is using 2.4 gamma. But, once I profile my display and go to export a LUT the Rec709 preset is using 2.2gamma.

So far I thought 1.8 is MAC, 2.2 is for PC, 2.4 is broadcast and 2.6 is DCI Cinema. However some people say, that there is no real standard gamma for Rec. 709 because gamma should follow the environment where the display is. If it is bright you use 2.2 or lower. If it is dark you go for 2.6.
Is it true that for example the difference between sRGB and Rec. 709 is 2.2 vs 2.4 gamma? I also read somewhere that it is not 2.4 but 2.35 for Rec709.
Crazy!

Where is the truth? What should I use?

George

Edit: sorry I just realized this is not the right topic.

Author Steve
Scene
#2 | Posted: 2 May 2013 08:26 
Most traditional CRT displays, when profiled, show a gamma of 2.2, so this is the default within LightSpace.

If you wan to generate a new Colour Space pre-set with a gamma of 2.4, or any other gamma value, you can do that by saving a new pre-set after first editing the existing Rec709 pre-set within 'Colvert Colour Space.

This is explained within the use on-line manual

But, as you say, there really is no 'standard' for TV Gamma.

Steve

Author aprilliasky
Mono
#3 | Posted: 2 May 2013 09:15 
Thank you Steve! I read all the manuals. The reason I was asking is, because the Rec. 709 "factory setting" confused me with the choice of gamma. I use 2.4 with my plasma and it worked well so far.

Author Steve
Scene
#4 | Posted: 2 May 2013 09:17 
Great - if that works for, stick with it!
It's why we made the pre-sets editable

Steve

Author Nepomuk
Mono
#5 | Posted: 23 Jun 2013 07:04 
Hello all!
If you grade for cinema resulting in a DCP with a 709 projector, I use 2.6 gamma anyway, right?

Thanks!

Author Steve
Scene
#6 | Posted: 23 Jun 2013 11:02 
You can set the gamma to any value you want, assuming the projector can do it, but we would suggest to profile the projector to make sure it is accurate, as many of the 'default' settings are not accurate...

As you will have to convert to P3 (or XYZ) you will have to do a colour space conversion, and most workflows will alter the gamma at that stage.

Steve

Author Nepomuk
Mono
#7 | Posted: 23 Jun 2013 17:09 
I always use a quick profile lut. Setting the projector to 2.2 gives a very good calibration (99%, a PD F32).

So grading in 2.2 and converting to 2.6 is possible? Theoretical it should work, but sounds scary to me.

Author Steve
Scene
#8 | Posted: 23 Jun 2013 20:46 
It works perfectly...


Author Nepomuk
Mono
#9 | Posted: 24 Jun 2013 05:55 
Thanks Steve, learned something again!

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