subband_coding_2005 - Lecture notes of Image Compression...

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Lecture notes of Image Compression and Video Compression 3. Subband Coding
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#2 Topics z Introduction to Image Compression z Transform Coding z Subband Coding, Filter Banks z Introduction to Wavelet Transform z Haar, SPIHT, EZW, JPEG 2000 z Motion Compensation z Wireless Video Compression
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#3 Contents z From DCT/DFT to Subband Coding z Filters z Low pass filters z High pass filters z Filter banks z Ideal filters z Realistic filters z Impulse Response of the Filters z Quadrature Mirror Filters z Application of Subband Coding z Relationship to Wavelet Transform Coding
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#4 Model and Prediction z Compression is PREDICTION . z Good model results in better prediction. z For text, we have good models (PPM, BWT). z For images, we are in need of a good model! Compressed Bit Stream Transmission System Model Model Probability Distribution Probability Estimates Probability Estimates Probability Distribution Encoder Decoder Source Messages Original Source Messages
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#5 Separate the Signals z Modeling a general signal is difficult. z However, most signals exhibit a combination of characteristics. z This signal can be decomposed into two signals (long term and short term), each can be simulated by an appropriate model.
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#6 DCT/DFT Spatially Decomposition z DCT/DFT spatially decompose the image into blocks. z Perform frequency domain processing in each block . z Discard high frequency information in each block, because human eyes are insensitive to high frequencies. z However, there are artifacts at the block edges. Coarser quantizatio n
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#7 Frequency Domain Decomposition z Instead of spatially divide the image into blocks (such as DCT/DFT), we can consider frequency domain processing on the whole image . z Filtering the image horizontally into two subbands (images). z Down-sampling horizontally. z Filtering subbands vertically. z Down-sampling vertically. z Model and code each subbands separately. z This is the subband coding . DCT / DFT 1 2 3 4 1 2 3 4
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#8 Subband Coding z Subband coding is a technique of decomposing the source signal into constituent parts and decoding the parts separately. z A system that isolates a constituent part corresponding to certain frequency is called a filter . If it isolates the low frequency components, it is called a low-pass filter. Similarly, we have high-pass or band –pass filters. In general, a filter can be called a sub- band filter if it isolates a number of bands simultaneously .
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#9 Filters z A system that isolates certain frequency components is called a filter . z Low-pass filter z Only let through components below a certain frequency f 0 z High-pass filter z Block all frequency components below a certain frequency f 0 z Band-pass filter z Let through [f 1 , f 2 ]
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#10 Ideal Filters z Ideal filters have a clear cut-off frequency f 0 .
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This note was uploaded on 06/09/2011 for the course CAP 5015 taught by Professor Mukherjee during the Spring '11 term at University of Central Florida.

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subband_coding_2005 - Lecture notes of Image Compression...

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