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Monday, December 2, 2013

How does a digital camera work - Part 2

In the last post I talked about how a film image is composed of millions of bits of silver blocking the light so that what could be seen could be reproduced although as a light-for-dark negative image.

But what about colors? We see colors and know that color photographs exist, so how do they do that?

There are two ways to do it. One is reflected and one is transparent. Think of the first as looking at a painting using colored pigments and the second as looking through colored pieces of glass.

I'm going to talk about color in a very simplistic way. Remember those 3-D books and movies where you wore cheesy cardboard glasses (technical term - anaglyphic) with one blue lens and one red lens? The images on the screen or page were very confusing when viewed with the naked eye but jumped off the page through those lenses.

The principle is simple. The lens passed the color that was the same and blocked the color that was opposite. Thus, the red lens passed the red color which made it seem the same as the background but blocked the blue color which made it seem black. The blue lens did just the same but for the other color. That meant that left eye looked through the red lens and saw the blue (now black) image and the right eye looked through the blue lens and saw the red (now black) image. The brain interpreted these slightly different images as the same but at different distances (parallax).

Back to our film with millions of silver bits that can only produce black and white. If we were to coat some of the bits with a filter agent so they could only see red, then we could tell where the blue in the image was. The same would be true of yellow and blue filters. Combine red and blue to get purple, look across the color wheel and you see yellow. Just the red filter and you can see green. So imagine taking three pictures of the same scene, one each through a red, blue, and yellow filter. When looking through the three images laid on top of each other all of the colors would be recreated.

I cheated a bit here. The real colors are red, green, and blue but you get the idea (hopefully). The filters over the sensitive silver bits are what make the difference between the colors.

See you soon for how this applies to digital devices.

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