Screens, contrast range, CRT PJ's, and human perception - AVS Forum
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post #1 of 2 Old 08-12-2001, 10:10 AM - Thread Starter
KBK
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I flung this one out into the void on the CRT forum, but it is really relevant here, as well, so.. here it is:

~~~~~~~~~~~~~~~~~~~~~~~~~

So where's the difference here? Why am I so adamant? These are the kinds of questions I have asked myself..about this very thing, long ago.
Why do I prefer the 1.5 gain area, over that of 1.3?

Think about it. I can get to any gain I desire. I can create any surface I desire. I HAVE made 1.0 to 1.8 gain screens...of all kinds of different characteristics and color temps, and grey levels.

I PERSONALLY have settled on the 1.5 area. I do not believe it is best for most folks.

Basically, I have found that 1.3 gain screens, or below 1.5 gain or so.. pollute their own surfaces way too much when it comes to contrast range that the surface is capable of..when used in conjuction with _MY_ CRT projector. In your case, this may not be as realizable, or obvious. Rest assured, I do very much love the color fidelity that can be achieved from having a low gain screen. But I cannot stand the loss in contrast range.

Higher gain screens create a wierd 'pressure' on the eyes, and give strange bent in the contrast 'character' at just below what people can understand, perceptively. This odd pressure, in a gain that is too high, is very unacceptable. If the gain is low enough, this strange 'obscuration' as you move ACROSS the image (near the center) will be very negligable,and thus, bring the impression of contrast range..and ease of viewing... to the human condition. You 'relax into' the proffered image. Very much like the effect when you are in some place..and the furnace finally shuts off... you relax. VERY IMPORTANT. Enjoy your PJ system. Don't mentally 'fight' with it. The more 'natural' the image, the less 'decoding' you have to do. Like when you are in a loud room, full of people, and trying to speak with the person beside you. You have to 'decode'.. and 'fight'... and 'sort'... and 'reject'.. and finally..'interpret', so you can understand. In a quiet room, you merely have to listen. A single task. HUGE DIFFERENCE.

Same with the screen.

Due to constructional considerations of screen design, lower gain screens (if properly made!) will have the greatest color fidelity AND show this ACROSS the entire image, at JUST bleow the threshold of noticability on almost every concievable image thrown at them.

Naturally, those who go fo this fidelity over any other.. tend to desire absolute color fidelity from the projector as well.

These people go out of their way to move into projectors with color correction, done in the fluid, lens, or filter material.. of some sort. These methods of color correction, obsure contrast range in a subtle manner.. but APPEAR to give more, simply due to the saturation. Logic involving the physics of the sitaution states that the filter will slightly obscure the contrast range available out of the filtered tube/lens assembly, and this is what I have seen and made note of. The APPEARANCE of greater contrast range is a function of the screen combination with that of the tube/lens, and the human equation. Of course, the most important factor is the human factor, or interpretation of the situation. The saturation brings about a 'punching up' of the DIFFERENCES between the three primaries, which brings about, in human realization terms... the APPEARANCE of greater contrast range and depth.

I have clearly NOTICED the effect of color filtering making previously useable higher gain screens.. have COLORSHIFT that is suddenly above the threshold of sensitivity. Due to the ultimate obsuration characteristic of lower gain screens, concerning thier ultimate contrast range (image noise floor pollution)... this effect of color filtering 'shortening the contrast range' is harder to realize.

~~~~~~~~~~~~~~~~~~~~~~~~~

Now, I have done EVERYTHING I can to use this 'effect' of 'differences' in primaries, to make it so that the contrast range coming out of the PJ is as high as humanly and electronically possible.

Remember the 'saturation effect' with the reds on a single chip DLP? They are FINE as long as the image does not contain too much red in it. The moment this happens, what was previously realized as red...sudeenly LOOKS orange to the HUMAN PERCEPTIVE interface.

This effect, told me everything I needed to know.

So, I went after maximum, correct contrast range in my PJ, over that of color filtering and lower gain screens. I needed the contrast range of the higher gain screen to get the sharpness, and contrast range out of the PJ. The higher level of immunity of the high gain screen, to 'cross-luminance-self-infection', gave me what I needed.

Now, after all that work..at creating a screen at 1.5 gain, that does not suffer from 'silvering', and getting as much contrast range out of the PJ as poossible, and the sharpness to boot.. I have the IMPRESSION of color saturation, well beyond that of standard fare, non-filtered PJ's. And, in the end, that's all that counts.

Also, the screen design, has as little of that 'pressure' problem as I can put into it, whilst keeping the contrast range as high as possible.

I'm having my cake, and eating it too.

And the 3-d effect? With running a very high contrast range HTPC, with zero effect on the noise floor (all I get is the PJ's 'rush' of transistor noise), no contribution there, from the HTPC, at all. And, running a very sharp 1920x1200@72hz out of it... and getting VERY subtle depth 'cues' from the thing as a whole? Man, oh, man. On the very best encoded DVD's, it's a monster.

But then again, I haven't seen much in the way of other PJ's. I have a friend who has a 1292, and 2 10pg's. He's seen it. He just shakes his head and walks away. I haven't looked at his PJ's yet.


------------------
goosystems.com

Ken Hotte
kbk@cyberfreak.dhs.org
kbk@goosystems.com

[This message has been edited by KBK (edited 08-12-2001).]

Ken Hotte

"Never forget that only dead fish swim with the stream." -- Malcolm Muggeridge.
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post #2 of 2 Old 08-14-2001, 09:48 PM
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Ken,

I find the science and tweaking of screens fascinating...it seems still an undertapped area for improvement...here's to your continued experimentation and success.

I'm sure your screen size is listed somewhere, but I can't find it now. I know you have a highly tweaked 8" CRT.

Also, I regularly follow the threads on torus screens...Have you tried simply a curved screen at home? It seems that even without computer models, an accurate horizontal curve ccould be obtained, perhaps allowing further gain increases. Wouldn't a single curve get you at least 1/2 the benefit of a torus, and therefore be worth it? It seems that the benefit would actually be higher in the horizontal axis than the vertical since the screen is almost twice as wide (16) as tall (9).

One day, soon I hope, I'm going to stir all this AV Science info together and upgrade to a killer system. I would like to tweak the screen too if able. Our hobby is so expensive though, that I can't afford to buy something and then replace it too soon..."measure twice, cut once" and all that.

Now if I could only figure out how much the copy-protection fiasco with HD is going to affect my plans.

Oh, yes...thanks for sharing your results!

------------------
Jeff
Currently - Zenith 7" CRT, 80x60 1.3 gain screen

Soon to be - 107x60 1.3 gain...with whatever higher rez DLP gets its act together (finally)with Panamorph or B stock/etc 9" CRT

[This message has been edited by Jeff Smith (edited 08-14-2001).]

Thanks,

Jeff

Finally went digital: RS20, ISCO IIIs, DIY 10.5' wide torus screen, Stewart StudioTek 1.3 G3 with 4 way masking and adjustable image size
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