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| Play Pixel This! |
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| The picture puzzles in the game do not contain very much information. Each one starts out with just a few large squares in different shades of gray. We can think of each square as a "picture element," or "pixel." The more pixels there are, the more details we see. This is how digital cameras work. |
 Click to play Pixel This! |
| 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? |
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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. |
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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!
 NASA's Planetary Imager project is working on making new CCDs that are even tougher and more sensitive that the ones now flying in space. One reason is that someday NASA would like to send a spacecraft to study Jupiter's moon Europa. Scientists think Europa may have a liquid ocean under a crust of ice. This ocean might be home to some tiny life forms. But Europa orbits inside Jupiter's very harsh radiation belts. This radiation is very, very hard on spacecraft instruments, especially cameras. So any camera that goes there is going to have to be really tough.
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