Color films use a minimum of three different layers of photosensitive emulsion, each sensitive to red, green, and blue light. Digital cameras have three sets of color sensors, and scanners use three light sources, three arrays of sensors, or filters to capture red, green, and blue information. Finally, when digital information is seen on computer monitors, the same three colors (in the form of LCD pixels or CRT phosphors) complete the circle by displaying the color information for our eyes to view again.
Digital cameras work something like color film, responding to red, green, and blue light. However, except for some alternative technologies, such as the Foveon sensor currently used only in the Sigma SD9 and SD10 digital SLR cameras, and the seldom seen Polaroid X530 point-and-shoot model, camera sensors do not have separate red/green/blue layers. Instead, each pixel in a digital camera image is sensitive to only one color, and interpolation is used to calculate the correct color for a particular photosite if something other than the color it's been assigned falls on that pixel.
The various capture and display processes are significant for an important reason. None of the systems used to grab or view color respond to red, green, and blue light in exactly the same way. Some are particularly sensitive to green light; indeed, digital cameras are designed with twice as many green-sensitive sensors than red or blue. Most systems don't respond to all the colors in a perfectly linear way, either, so that a hue that is twice as intense may register slightly less or a bit more intense.
And it gets worse: The models used to represent those colors in the computer also treat colors in different ways. That's why an image you see in real life may not look exactly the same in a color slide, a color print, a scanned image, on your screen, or when reproduced by a color printer or printing press. Simply converting an image from RGB to CMYK (more on that later) can change the colors significantly. The concept of the range and type of colors that can be captured, manipulated, and reproduced by a given device or systemits color gamutis an important one for photographers working in Photoshop.
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Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.