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The picture puzzles in the "Pixel This" game contain little information. Each one starts out with just a few large squares in different shades of gray. Each square is called a "picture element," or "pixel." The more pixels there are, the more details we see. This is how digital cameras work.
Cameras used on spacecraft are similar to digital cameras, except a lot tougher and a lot more sensitive. Instead of film, cameras on spacecraft have special light-sensitive devices similar to computer chips. These are called charge-coupled devices, or CCDs. Each CCD is made up of hundreds of thousands (or millions) of tiny pixels.
When the CCD camera takes a picture, it converts the pattern of light into a pattern of numbers. The highest numbers represent the brightest parts of the scene. Zero would represent black. Everything in between gets a number based on how bright or dark the shade of gray. But what about colors?
For each color picture, several pictures are taken, each through a different colored filter—like looking through different colored sunglasses. Each filter lets through only a certain color of light. For example, a red filter lets through only red light. So the red-filtered pixel data will show the brightness of the red colors in the scene.
After computers on Earth combine the pixel data from three pictures, one taken through a red filter, one through a blue filter, and one through a green filter, we can see the original colors in the scene from space—and all from shades of gray!
