ITU-R BT.1886 Gamma formula?

[Anonymous]

Should we be transitioning over to the ITU-R BT.1886 gamma formula when possible in calibrations, when the customer has good light control? Right now I use power function.

Topic

[Gregg Loewen]

hi
short answer is yes.

[Anonymous]

Thanks Gregg!

[Gregg Loewen]

the more precise answer is 2.40 gamma.

This would be a good discussion to have over beers (or diet cokes).

Merry Christmas!!

[Anonymous]

Can someone help me understand why the gamma formula impacts the saturation sweeps.. I’m not clearly seeing the relationship. I have just discovered that if I start with a WF that was saved with a power formula and I do a sat sweep, it doesn’t do a 0 read (which is correct). However, if I change the gamma formula to 1886, then it changes the layout and takes the 100/0. Now the issue I noticed is that if I try to switch back to the power formula, it still reads 100/0. I was doing this with all older workflows and the THX complete as a test. It seems that if it was initially created with power, it works until the formula is changed. Then, it takes a restart of CalMAN to get back to not reading 0.

What has me curious is that if a display can go lower than a meter can read (thinking of a full array backlight and a meter that can’t read that low), then it seems that the 0 will be blown and thus the math is compromised. Is this even remotely correct?

[Gregg Loewen]

hi Terry

Think of the canvas as a light source that changes the brightness of the paint. As the canvas becomes brighter, the paint will be less saturated but of a higher luminance.

yes on IDing potential problems trying to measure 0 % stimulus. Upgrade your gear, or more realistically stick to gamma of 2.3 ish.

[Anonymous]

Thanks Gregg…

What I was getting to, in a round about way -My question seems to evolve with discussion, is that if one goes from 1886 to power, then it seems that also requires a change in the gamma points to get it to NOT read 0 in a saturation sweep (also a restart). At least that is how the software is behaving. Also, if I understood a response I received elsewhere, 0 is not required if using power; however, I am wondering what it is doing when it is set to power and the scale is set to 11pt. Is it using the 0 measurement or not. It seems like from the response I received, but I need to follow-up -If a 0 is specified, then it won’t read 0 or use it (not sure on this exactly).

But, the question I haven’t answered in my mind is what is happening if I leave 0 measured and use only a 10pt. This can happen because of the new default. So, I was trying to understand the components needed to create the sweep, and see if I can determine what is happening, based on the settings I change. IN the simulation mode, I think it is nearly impossible, since it may not be pulling any data and just generating random example data. so, the gist is, if I want to change the workflow from 1886 to power, what changes to the various settings need to be changed in CalMAN? Power, gamma pts, and 0 read, or will it correct itself if I just change to power, and don’t change anything else…??

Maybe this is best addressed on SpectraCal Forum, but sometimes I get some answers that leave me with just as many questions, so I thought I would try here to see if I can get a little insight.

So, thanks to all for help… It is invaluable to have so many knowledgeable resources.

[Author]

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