How does my projector make the color black? I can grasp the concept of making white. White is easy to understand. It’s the combination of all three primary colors and white and usually associated with bright light. But how does the projector create very dark colors and perfect black? It can created the perception of nighttime in a dark alley, by projection light onto the screen. (In this case, the screen is my wall. And my wall isn’t black.)
I obviously am missing some key elements in how these things work and what they’re doing.
Just so it’s clear, I’m not talking about movie projectors or filmstrip style projectors that are just shining light through film. I’m talking about the kind a person would normally use to put on a presentation or powerpoint through his laptop.
It is just contrast. The lit up areas make the nonlit up area look darker in comparison. The eye/brain is then fooled into thinking it it must be black
Doesn’t matter what kind of projector it is, the only way it can make black is by not shining any light at all on some part of the picture. Your wall may not be black - the average cinema projection screen isn’t either - but if you don’t shine any light on it, it doesn’t very much matter what colour it is. You’ve got no light coming back from that part of the picture, so you see black.
The lower the ambient lighting conditions, the blacker your black will look. Also, the brighter the bright parts of the picture, the blacker your black will look, because your eye adjusts to the overall brightness.
Mainly because in that situation, a steady beam of white light is projected through the film which acts as a color filter. I know that when I look at a the filmstrip or slides or something, I can see the whole picture and all the colors. And the light shined through it will be filtered through that picture and be projected on the wall. I guess I didn’t think about it in depth enough to realize that all a perfect black filter is, is something opaque enough to not let any light shine through.
Convince yourself of it like this. Gin up a powerpoint slide that has a big black patch. Make sure it’s really #000000. Project it. Take a white piece of paper, stand up next to the screen, and move it from outside the screen to in front of the screen in the “black” area. You will not see your white paper suddenly turn black.
As mentioned, a lot of color perception is managed nicely by the brain. It tends to adjust perception to ambient lighting conditions; sunlight is a different color than incandescent light bulb light but you wouldn’t notice it unless you could compare them side by side.