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Re: [Phys-l] Projecting Black



This is consistent with the Retinex model proposed by Edwin Land. You judge color and gray scales by comparing across boundaries. He used, as I recall, an analogous diode network to simulate the way the eye works. The color constancy under different illuminations is "fooled" by the projection. However if you show a movie on a whiteboard, it will usually wash out a bit, with greyish blacks. This effect is obvious across sharp boundaries.

Most textbooks never mention that the 3 color model is only approximate and that they eye is much more complicated in how it works. The processing immediately behind the retina is quite large, and it seems as if color constancy is produced there. From the point of view of biologists color constancy is often cited as the most important artifact of how we process color, while physicists and engineers concentrate on the 3 color model, and try to make it exact. This is impossible, and is often the reason why pictures, TV, and movies have off color.

John M. Clement
Houston, TX



Thanks, Rick. I'm wondering, though, how that "black" is transferred to my
Smart Board. It is quite "white" when no projected light hits it. Ron

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Rick Tarara
Sent: Tuesday, November 06, 2007 3:44 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Projecting Black

I think--just looked carefully at a black spot on a computer screen--that it

is simply that black does not illuminate any of the red, green, or blue pixels. On an LCD screen, none of the pixels are activated.

Rick

----- Original Message ----- From: "Ron Curtin" <ron.curtin@charlottecountryday.org>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, November 06, 2007 3:35 PM
Subject: [Phys-l] Projecting Black



A student asked me a question that I couldn't answer. When I pick up the
black pen on my Smart Board, I can write with a really black color --- much
blacker than the appearance of the screen with no illumination at all.
Where does the black come from? I can produce most all the other possible
colors with a combination of the primary colors of light, but if I add all
the colors of light together, it seems like I should get white, not black.
Any help?

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l