Local Decompression Buffer + Audio samples
or image pixels - Coding 0101… Q + Lossy Predictive Coding
General Prediction Method
C B A X A B C D X For image:
For Audio:
Issues with Predictive Coding
Not resistant to bit errors.
Random access problem.
Transform Coding
1 3 4 5 3 2 1 0 3 4 5 6 2 4.5 2.5 0.5 3.5 5.5 + + + + + + 1 3 4 5 3 2 1 0 3 4 5 6 + + + + + + - - - - - - ½ ½ ½ ½ ½ ½ -1 -0.5 0.5 0.5 -0.5 0.5 ½ ½ ½ ½ ½ ½
Transform and Inverse Transform
y1
y2 = ½ ½
½ -½ x1
x2 We did a transform for a block of input data using The inverse transform is: x1
x2 = 1 1
1 -1 y1
y2
Transform Coding
A proper transform focuses the energy into small number of numbers.
We can then quantize these values differently and achieve high compression ratio.
Useful transforms in compressing multimedia data:
Fourier Transform
Discrete Cosine Transform
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