| Subject: | Optics question ........ projection screens |
| From: | TheMekon |
| Posting date: | 26-02-2008 |
| Content: | |
I need to show a customer what a High Contrast prpjection screen looks
like - one with a gain of 0.4
I want to show them a matt white screen next to it
I want to project the same image onto samples of both screen materials -
ie one next to the other
I want to adjust the image I am using so that the peak white from the 2
materials is the same - so, given that the 2 screen samples are
horizontally next to each other, I want to divide my image in two, one
half is unprocessed for the 0.4 gain screen the other half processed so
that the matt white screen gives me the same peak white.
Are you still with me?
So it seems obvious that I use photoshop on my image, and use "curves"
to map input:output to only use 40% of full scale on the output.
40% x 255 = 102
Lets test this theory, make a test image of a white rectangle, on one
half of it apply "curves" as above.
If my theory is right, the two adjacent parts of the image on the two
adjacent screens will have the same apparent brightness.
My theory is wrong. The two screens look totally different - the white
screen illuminated by the "40%" image i much darker than the 0.4 screen
illuminated by the "100%" image
I'm now confused. My head hurts.
If anyone can explain what is going on I would be most grateful.
Thanks
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