09-03-2012, 05:42 AM
09-03-2012, 09:15 AM
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27-07-2012, 11:12 AM
Wavelet Transform
2003-Wavelet Transform.ppt (Size: 367 KB / Downloads: 56) Haar Wavelet Transform To calculate the Haar transform of an array of samples: 1. Find the average of each pair of samples. 2. Find the difference between the average and the samples. 3. Fill the first half of the array with averages. 4. Normalize 5. Fill the second half of the array with differences. 6. Recurse - repeat the process on the first half of the array. (Note: The array length should be a power of two) Encoding the Coefficients How do you encode the coefficients effectively? Various ad hoc methods Store 0 if coefficient is below some threshold Store coefficient if > threshold as (x,y,c) Suboptimal approach. Bad compression. EZW – Embedded Zerotree of Wavelet Coefficients Developed by Shapiro in 93 Enabled wavelet compression to compete with JPEG Builds on two observations: Large coefficients are most important (contains most information) and should be stored first. Magnitude of coefficients decrease as one moves from lower frequency subbands to higher frequencies. E: Embedded. Progressive algorithm Z: Zerotree. Quadtree data structure central to algorithm W: Wavelet. Designet specifically for wavelet compression |
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