AVS Special Member
Join Date: May 2000
Location: Thousand Oaks, CA
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|PANARAMAX - "Minute flat black polka dots all over the screen will work better. Or a movie theater perf screen with black backing. Or a curved screens works best. But no gray."|
|Terry McCracken - "When we wished to have a colour background we would put a colour filter over a strobe and light up the background paper with it. If you put in a black paper, then your strobe had to be very powerful to bring the background back up to a reasonable level. So, what we did was have a series of grey rolls of backing paper, several shades of grey. We would put in the shade of grey,as measuered by the light meter, that would appear black to the camera, this was done by knowing your exposure for the subject and then measuring the light reflected by the backdrop, if it was 6 stops below, then it would appear as black on the film, no need to go further than that. Then the colour strobe would be set to light up the background to a particular exposure depending on the level of colour we wanted. We used to set this up by shooting a role of film, we would shoot the background at each stop, the equivilant of shooting a 20 ire window, a 30 ire etc. We would develop and print. We would then have a reference knowing that if something in the shot was 2 stops down from the reference exposure what it would look like on film all processing included. So, my thinking is that this should also apply to video projection. You would set up in your room with the ambient light and try various shades of grey untill the screen looked black under those conditions, then turn on the projector and set the brightnessn and contrast. The pedastal light level caused by the ambient would be absorbed by the grey and the projector picks up from that point and produces the image. There is no reason that I can think of that would stop this producing a good image with excellent blacks.|
"What is the theory behind polka dots?"
" It is well known that the eye and brain are non-linear. Your eye has an AGC and your iris in your eye sets an f-stop. Blacks hence become blacker in bright light because less light hits the retina. The correct level of grey can be determined empirically. A raised polka dot could block ambient without impacting reflected light. Another way of doing it would be a perforated black screen with white shadowed background.