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-   -   Screen/m2500/painted wall & contrast q's (http://www.avsforum.com/forum/23-screens/18925-screen-m2500-painted-wall-contrast-q-s.html)

pcostanz 02-29-2000 08:31 AM

I have a NEC LT80 600 Lumen projector and the tested specs by PCMAG are almost identical to the Davis DL450.

The problem is that I am using a painted wall for the screen with Ceiling white surrounded by a flat black border. The contrast is poor and the image is not very bright. I'm wondering if switching to a m2500 draper will improve contrast and brightness.

Also, it seems that the contrast became worse or non-black blacks were more noticeable whem I painted the surrounding area flat black. When it was tan the DLP blacks looked blacker. Is there a standard for painting aroud the screen?

Thanks for all the help.

Dean McManis 02-29-2000 03:13 PM

A flat painted wall generally has a gain of 1, whereas the M2500 should have more than twice the light gain.

I went from a 1.3 gain screen to the M2500 and saw a visible improvement in color and contrast as well as brightness.

If you are curious, you might call up Draper and have them send you a M2500 sample swatch that you can tape up to the wall and compare to the flat paint picture.

-Dean.

Federico 03-11-2000 07:32 PM

I'm using an LT81 projected over a flat screen and last week I painted the surrounding wall and the ceiling gray that used to be white, and the inprovement was great, adn the t.v. looks better too, because the ceiling doesn't reflect on the screen. Try it.
Federico

Guy Kuo 03-11-2000 07:49 PM

pcostanz, the decrease in apparent contrast ratio when you changed the front wall from tan to black is probably due to the "dark surround" vs "light surround" effect. When the image area is surrounded by a light color we perceive the image as having greater contrast. The effect is about the same as increasing image gamma by about 0.3. Darkening the surround reduces apparent contrast ratio. This is probably why the APPEARANCE of black seems lighter now that the front wall is black.

The objectively measured black level is probably the same or perhaps slightly better with wall scatter being reduced by the black paint.

The dark surround effect is often forgotten in the quest for blacking out a room. If your room is already blacked out and want to see this effect, sit in front of the screen and place a laptop computer screen such that it takes up about the same subtended angle as the projection screen and situated below the screen. Turn on the laptop screen on and off and note what happens to perceived contrast. When the laptop screen is lighted, blacks look darker on the projection screen.



------------------
Guy Kuo
www.ovationsw.com
Ovation Software, the Home of AVIA DVD




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