Pyramid Coder with Nonlinear Prediction

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Pyramid Coder with Nonlinear Prediction
Panu Chaichanavong

• Burt/Adelson pyramid coder
• A nonlinear prediction
• Aliasing effect
• A switching method
• Conclusion

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Burt/Adelson Pyramid Coder
Introduced by Burt and Adelson (1983)
Gaussian
Laplacian
Quantized
and transmitted
Original image
Reconstructed image
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A Nonlinear Prediction
By Florencio and Schafer (1994)
Filter Just subsample!
Interpolator

1. Replication
2. Weighted median of 6 neighbor pixels
3. Median of 4 neighbor pixels

• 1 1
• 1
• 1 1

1 2 1 2 3 2 1 2 1 2 3 2 1 2 1
Lower resolution image
Predicted image
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A Nonlinear Prediction (2)
Burt/Adelson coder
with nonlinear prediction
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Aliasing Effect
Test image
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Aliasing Effect (2)
Gaussian filter
Only subsampling
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A Switching Method
Lets look at the following 4x4 filters
.032 .058 .058 .032 .058 .102 .102
.058 .058 .102 .102 .058 .032 .058 .058 .032
0 0 0 0 0 0 0 0 0 0 1 0 0 0
0 0
0 0 0 0 0 1 2 0 0 3 4 0 0 0
0 0
Filter3 Linear low-pass with weight shown above
Filter2 Median of average
Filter1 Pick one !
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A Switching Method (2)
Input1
Input2
Input1 may be an edge, use filter1 Input2
high frequency, use filter3
How can we distinguish these inputs?
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A Switching Method (3)
Let D sum of difference of adjacent pixel
values sd standard deviation of 16 pixel
values p D/sd
Decision criterion p lt 18, use filter1 18 lt p lt
22, use filter2 p gt 22, use filter3
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A Switching Method (4)
Filtered subsampled image
Filter used
Filter1
Filter2
Filter3
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A Switching Method (5)
Method PSNR (dB) Bit-rate (bit/pixel)
B/A 32.77 0.8278
Nonlinear 34.00 0.6544
Switch 33.58 0.6501
Reconstructed image
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A Switching Method (6)
Images in the Gaussian pyramid
Filter used
Filter1
Filter2
Filter3
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Conclusion

• Low-pass filter reduces aliasing effect but gives
  blurred image
• Some nonlinear prediction preserves edges and
  details but may introduces annoying aliasing
• A decision criterion is presented to switch among
  various filters to select an appropriate one for
  a particular input