APPENDIX A
The Discrete Cosine Transform
The Discrete Cosine Transform, or DCT, is used throughout the MPEG standards as a way to provide video compression. This mathematical tool allows images to be represented with amazing visual accuracy (at least within the limits of human perception) with far fewer bits than those needed to create the original image.
The DCT used in MPEG operates on 8 pixel by 8 pixel blocks of image data. Luminance and the two color difference signals (see Chapter 3) are compressed separately by MPEG, but they use the same DCT principles. Figure A-1 shows a simple before-and-after picture of the DCT process. At the input to the DCT, an 8×8 block of pixel data is present. At the output from the DCT, an 8×8 block of data ...
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