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What useful information i can take from the coefficient intensity maping after performing DCT transform?

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The DCT is used in many places for its "energy compaction" properties. This is mostly useful in compression. For example, if I have a signal and I take its wavelet transform, then I can "compress" the signal by throwing away certain coefficients. These coefficients are not known before-hand. I have to look at the wavelet coefficients and then throw away all coefficients below a certain threshold to achieve some amount of compression with an acceptable loss in reconstruction accuracy.

For the DCT however, most of the energy of a signal is collected in its "low" frequency coefficients. What that means is that if you only keep the first lets say N coefficients (you don't need to store the locations of which coefficients you kept), you can get decent compression. In 2D, a "zonal" or "zig-zag" pattern is used to choose the coefficients to keep.

On a more fundamental level, the DCT is basically a linear combination of your signal as a bunch of discrete cosine waves. If you think of each cosine wave as an elementary building block, then the DCT tells you how much contribution to your image comes from a discrete cosine of a particular frequency.

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