Will projecting on a Grey wall decrease contrast? - AVS Forum
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post #1 of 5 Old 10-30-2001, 05:46 AM - Thread Starter
Ran
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I just upgraded my Sony 10 HT to a Sharp XVZ-9000. I am projecting on a Grey wall, which did wonders to the Sony's poor black level. The Sharp on the other hand has a very high contrast ratio (1100:1) so its black level as a result are superior to the Sony. The picture looks very good on the Grey wall, But I wonder if by doing that I'm actually decreasing the Sharp's contrast or perceived contrast?
Will projecting on a white wall, as opposed to the Grey wall, improve contrast?
Thanx
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post #2 of 5 Old 10-31-2001, 06:34 AM
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get either avia or video essentials and tweek it. I played with the best shade of gray for my projector. You might not need as dark of gray as you have but you might be supprised with how good it looks with it adjusted right...:)

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post #3 of 5 Old 11-01-2001, 09:30 PM
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Ran,

A grey wall should *increase* your contrast by absorbing light reflected back by the walls of your room. If you were to measure your projectors contrast ratio you would find that your ANSI contrast would increase when using a grey surface, although your on-off contrast would remain the same.

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Kam Fung
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post #4 of 5 Old 11-03-2001, 05:18 AM
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Kam,

Remember that the system is linear. The brightness of the ANSI pattern white sections is reduced for the grey screen and therefore also the light reflected back to the black sections. Contrast ratio remains the same regardless of screen if there is no background light. Only if the screen significantly changes the reflective properties of the room, the suppression of higher order reflections may increase CR for the grey screen.

However, for digital PJ's there is often a need for reducing the maximum brightness. Since the black level is fixed, this will reduce the contrast ratio if the projector peak output is reduced. Using a grey screen will reduce both maximum brightness and black level, keeping CR constant.

Subjectively it seems that absolute black level may be just as important for PQ as CR, at least for some viewers. The grey screen obviously provides benefits here as well.
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post #5 of 5 Old 11-03-2001, 05:20 PM
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Quote:
Only if the screen significantly changes the reflective properties of the room, the suppression of higher order reflections may increase CR for the grey screen.
That's exactly what I am saying! :) I am aware that the system is linear which is why I stated earlier that on-off contrast should be the same, the changes in ANSI contrast are a direct result of reducing the effect of second order reflections. The light reflected by the white squares in the checkerboard has a profound effect on the black squares, which is one of the reasons why real-world ANSI contrast measurements are generally lower than simple on-off measurements. The secondary reflections from the white square is essentially background light.

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Kam Fung
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