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Synthetic Aperture Radar ImageCompression
By
Magesh Valliappan
Guner Arslan
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Synthetic Aperture Radar (SAR)
✔ SAR ?– Active imaging system– Working in the frequency range 1-10 GHz– All-weather system– High resolution compared to real aperture radar
✔ Applications– Agriculture, ecology, geology, oceanography,
hydrology, military...✔ Nature of SAR images
– High volume of data– Speckle noise– More information in high frequencies than optical
images
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Lossy Image Compression Techniques
✔ Joint Photographic ExpertsGroup (JPEG)– Discrete Cosine Transform
– Fast implementation
– Blocking artifacts
✔ Set Partitioning InHierarchical Trees (SPIHT)– Discrete Wavelet Transform
– Good visual quality
– Ringing effect for high compressionratios
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Quality Metrics for SAR Images
✔ Standard Metrics– Mean Squared Error (MSE)
– Signal to Noise Ratio (SNR)
– Peak Signal to Noise Ratio (PSNR)
✔ Other Metrics for SAR Images– Weighted Signal to Noise Ratio (WSNR)
– Linear Distortion Quality Measure
– Correlation of Edge Information
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Simulations
✔ Space borne Imaging Radar-C and X-BandSynthetic Aperture Radar
✔ 512 x 512 Sub-Images
✔ 8 bit grayscale
✔ Pre-filtered by a modified σ-filter
– adapted to handle spot noise
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Estimation of a Linear Model
✔ Linear Least Square Estimate
✔ Linear Model is needed to– compute the Noise Image
– estimate the Distortion Transfer Function (DTF)
✔ Drawbacks– Model assumes uncorrelated additive noise
– Variance of the estimate
H
NoiseImage
SARImage
Compression De-compression
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Linear Models
SPIHTJPEG
CSF
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Correlation of Edge Information
JPEGSPIHT Original
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Results - WSNR and PSNR(d
B)
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Results - Linear Distortion Measure
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Results - Correlation
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Conclusions
✔Standard metrics does not give resultsconsistent with visual quality
✔A framework for evaluation of SAR Images– Weighted Signal to Noise Ratio
– Linear Distortion Measure
– Distortion of edge information
✔SPIHT outperforms JPEG