how do projectors make the color black on white screens?
In: Technology
It does not. Black will be the absence of any light from the projector so it will have the same color as the surface you project on.
So you need a projector that emits a lot of light so the areas around it look a lot brighter and you see the unlit white areas as a lot darker.
Grey as a color is white with less light intensity compared to the surrounding.
Look at [this image.](https://en.wikipedia.org/wiki/Checker_shadow_illusion#/media/File:Checker_shadow_illusion.svg) square A and B have the same color but you think of A as gray and B as white because of the surrounding areas and the shading you see from the green object. If you open it in an image editor and pick the color they are the same, you can do the same by cutting holes in a paper so you only see those squares.
So human vision is based on the light relative to the surrounding not the absolute amount of light
The dark color in a projected image in a well-lit room will look washed because they are a lot brighter because of light that does not come from the projector
There is a reason that in a cinema you turn the light off in the theater so very little light hits the area that should be black.
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