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I have a movie projector which is projecting an image on a brown wall. The projector allows me to adjust 6 values. Red brightness, Green brightness, Blue brightness. Red contrast, Green contrast, Blue contrast.

Is it possible to "cancel out" the color of the brown wall by adjusting the RGB values of the projector? By cancel out, I mean so that the end result of the projected image is equivalent, as if the wall was a more neutral gray or white.

If this is possible, is there a way to do it without an expensive colorimeter? Maybe with some image processing from a phone camera?

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  • $\begingroup$ Wouldn't it depend on what colors the wall reflects? If it's painted with en.wikipedia.org/wiki/Vantablack you won't have much luck making it reflect white. $\endgroup$ – endolith Jul 20 '17 at 21:50
  • $\begingroup$ Ha hopefully not that intense. But a darker color should still work (like a gray). $\endgroup$ – Kevin Nasto Jul 21 '17 at 3:24
  • $\begingroup$ But you get the idea? If the wall is white, it reflects all colors, so illuminating it with only red will make it red. If the wall only reflects green, then it's not possible to make it red. The red will just be absorbed and it will stay black. In reality probably all walls reflect some of each color? But it depends. $\endgroup$ – endolith Jul 21 '17 at 3:36
  • $\begingroup$ If the wall reflects 'half' green, what would happen if you reduce the projector's green RGB value by half? $\endgroup$ – Kevin Nasto Jul 21 '17 at 3:42
  • $\begingroup$ It would be darker green? $\endgroup$ – endolith Jul 21 '17 at 4:46

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