Question About Gain's Effect - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-08-12, 02:20 PM
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Don

Join Date: Oct 2007
Location: Central PA
Posts: 3,772
Re: Question About Gain's Effect

Quote:
j0nnyfive wrote: View Post
Those images are trippy... whoa...

Embarrassingly enough, I had to copy that checkerboard image into Microsoft Paint, zoom in, cut and paste from the 2 squares and compare them myself. Whoa. I can't believe it. They look so different in the picture.
That moving picture. That's really moving. I know it is. lol Crazy man.
Oh yea of little faith... Just kidding! Trust, but verify.

On a more serious note, things like this are why we must use instrumentation to determine things like screen color neutrality and peak gain. The human eye just can't cut the mustard, it is too easily fooled.

Quote:
I think I may be making a fundamental error in my assumption of how gain works. Correct me if I'm wrong here. Assuming you are sitting perfectly on axis (and are ignoring hot spotting), does gain increase the brightness of the image uniformly across all shades of gray (including black and white)?
Yes.

Quote:
So, does it make sense to say "X% increase in gain will increase the brightness of any projected shade of gray by X%?" For instance, could I increase the gain of the screen so that I would get a predictable 20% brighter image no matter what shade of gray I show on the screen? I could show white, and I would know it would be 20% brighter than before. I could show my darkest black, and I know (assuming it isn't perfectly black) that I would get 20% brighter black than before? Is that how it works?
Yes. That is exactly what a peak gain value of 1.2 denotes - the screen on-axis will produce a 20% brighter image than a screen with a gain of 1.0.

Quote:
That was an assumption I was making in my question (that the change in gain effects all shades (brightnesses) by the same percentage). If this assumption is wrong, then my question is nonsensical. lol
There are a few commercial screens that actually have an engineered surface that acts like multiple optical lenses in manipulating reflected light, but even they must obey the laws of physics.

Quote:
I'm going to have to study up on dynamic range now! I'm soakin it up! That's interesting about the clipping. As a side question, where would be a good site to go to learn about calibration (for free if possible)? I would love to learn how to calibrate! That would be awesome. Thanks again!
Better watch it! This stuff can get addicting you know.

Calibration can be as simple as using a commercial DVD containing the THX Optimizer to set PJ brightness and contrast or as complicated as you want to make it, including needing thousands of dollars of equipment and software to perform. Mech is much more into calibration than I am since my PJ has only rudimentary color adjustments.
Harpmaker is offline

Old 02-09-12, 08:15 AM Thread Starter
Shackster

Join Date: Jan 2012
Location: NE AR
Posts: 76
My System
Re: Question About Gain's Effect

Nice. Thanks Harp and Mech! Yes, this stuff is definitely addicting. Love it though.

I think I'm understanding the answer to what I was looking for much better now thanks to you guys' explanations! I think I was just basically trying to understand the relationship between gain and contrast ratio.
I think I understand now that although you may possibly, on the surface, desire more gain, your contrast ratio limits you to how high you can crank it before you pull too much darkness out of your blacks. (Correct me if I'm wrong in any of this.) So, if you needed more gain for any reason, you would need to have a good enough contrast ratio, and your black level needs to be low enough to allow you some headroom. Otherwise, if you lose your blacks, you lose that perceptual contrast "anchor" in your picture.

Gotta tell ya I'm excited about painting my new screen that I haven't received yet (Sintra is kinda hard to get a hold of for me at the moment, but I have high hopes)!

Thanks guys!

P.S. I remember wbassett (is his name Bill?) making a remark recently about going in a new direction with his projection setup or screen setup or whatnot, and, if I remember correctly, he mentioned it being something that we may not be thinking. Gotta admit, I'm going crazy with anticipation here. lol Do you know what he's talking about? I gotta know.
j0nnyfive is offline

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