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APPENDIX E: Image Processing > DIGITAL PHOTOGRAPHY - Pg. 319

Appendix E: Image processing In order to process an image on a computer system, the image must be converted to digital form. PCM, which we discussed earlier, is most frequently used for audio, but it can be applied to conversion of an image from analog to digital. However, the pro- cess is more complicated than it is for audio. The first step for an imaging device is to convert photons of light to an electri- cal potential. Then the image is scanned, in a method that is the same as when the image is eventually displayed. Scanning results in a series of pixels. Here's how it works, in rudimentary terms. A pixel has characteristics that can be described in terms of its red, green, and blue components. Each of these has an intensity value, which maps to a code word. The pulse is the temporal relationship of pixels, and each pixel represents a sample. Again, modulation is a result of varying the amplitude of the sampling clock. Installation of a circuit board with video input and output in a computer system is necessary to capture and digitize video. These "frame grabbers" were the first steps in the emergence of digital imaging; they converted frames of video to files of data.