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What Do the Gamma Settings Do?


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#1 of 7 OFFLINE   Larry Talbot

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Posted December 13 2003 - 03:26 PM

I have a basic understanding of the grayscale. Use the cuts and the drives (sometimes called bias and gain?) to affect the high and low end of the scale, shooting for D6500k across the board.
But my Z1 LCD projector also has gamma settings, and I'm not sure how to eyeball those. With the cuts and drives I know you are aiming for the proper balance of red, green and blue, but what are you supposed to do with the gamma settings? Am I correct in thinking this affects the intensity of the light? To make sure that, say, a 100IRE screen is really 100IRE? How would you use such settings, if you wanted to tweak them by eyeball?

#2 of 7 OFFLINE   Larry Talbot

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Posted December 14 2003 - 05:19 AM

No one is willing to take a shot at this? None of you know what the gamma settings are or what they do?

#3 of 7 OFFLINE   Gregg Loewen

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Posted December 14 2003 - 05:52 AM

Gamma controls the intensity of light output as the projector moves from black to white ( 0 to 100 IRE ).

With some analyzers (like the Milori / colorfacts), you can actually measure / plot the gamma curve. The spec is 2.2, and persons such as Joe Kane, are wanting 2.5 as it helps digital devices look better with blacks.

Some projectors not only allow you adjust a global gamma but also red blue and green specific gammas.

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Gregg Loewen

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#4 of 7 OFFLINE   Larry Talbot

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Posted December 14 2003 - 06:02 AM

Thanks for the answer Gregg!

Am I correct in assuming it would be useless to try to eyeball gamma without, at the very least, a light sensor?

#5 of 7 OFFLINE   Gregg Loewen

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Posted December 15 2003 - 03:11 AM

you can try to do some eye balling of gamma.

Use a gray scale gradient pattern, and look at the lower portion of the scale.

Remember that after any tweeking, always look at some real material (and not just test patterns) before giving a thumbs up.

Regards

Gregg

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#6 of 7 OFFLINE   Larry Talbot

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Posted December 15 2003 - 07:24 AM

"Use a gray scale gradient pattern, and look at the lower portion of the scale."

Could you offer any specifics or steps on how to do this? (I assume my objective with gamma should be to get the proper light output, I want 100IRE to put out the correct amount of light, same with 20IRE, etc, right?)
I have a relatively decent monitor which has a D6500k setting (I know it is probably not even close to perfect but it's definitely better than my Z1). I've set my monitor up so that I can watch it and my big screen at the same time, looking back and forth from one to the other (the monitor is of course facing away from the screen, so I don't have to deal with reflected light from the screen striking the monitor and light from the monitor doesn't spill onto the screen either.)
I've been using AVIA grayscale images, trying to get the Z1's grayscale reasonably close to the monitor's. Do you think this method would be at all helpful when setting gamma?

Thanks again for your advice, Gregg!

#7 of 7 OFFLINE   Gregg Loewen

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Posted December 16 2003 - 02:09 AM

If your using a typical tube set as a reference for gamma...

put up a gray scale step pattern (steps of 5 0r 10) and adjust the gamma so you can see all of the steps (paying close attention to the lower steps). You will need to correctly set the contrast and black level first.

Regards

Gregg

The Sonodome - circa 2001
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Gregg's DVDs updated...sometimes
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