1. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 PS221 Project Presentation Pattern Sensitivity and Image Compression

2. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Presentation Summary The Human Visual system sensitivity to frequency Jpeg2000 compression scheme contrast sensitivity functions subsampling different color spaces choice of the best color space for compression color transform wavelet transform quantization : visually weighted steps

3. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Contrast Sensitivity Functions The eye’s sensitivity is different for : Black/White, Red/Green, Blue/Yellow channels Data from s-cielab Black / White Red / Green Blue / Yellow

4. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002

5. GUI used for the experiments This is what the Matlab Gui looks like :

6. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Comparing the color spaces The differences in the subsampled image reflect the efficiency of the space for compression The color space YCbCr performs best and is more compressible than Lab RGBYCbCr Lab

7. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Example in YCbCr With hardly any details in the chrominance the image is close to perfect Y Cb Cr

8. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Jpeg2000 This is what the general scheme looks like Color Transform Discrete Wavelet Transform Quantization The color transform is RGB -> YCbCr The discrete wavelet transform decomposes the image in subbands Each band is quantized according to its visual transform Jpeg is also analyzed in the report

9. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Wavelet trannsform Image Filtering of the lines f2 2f1 2 f2 f1 2 2 f2 f1 2 2 Filtering of the columns 2f1 f2 f1 2 2 f22 f1 2 2 First Level Decomposition Second Level Decomposition HH1 HL1 LH1 LL1 HH2 HL2 LH2 LL2

10. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Example of a transformed image HH1 HL1 LH1 LH2 HH2 LH2

11. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Quantization For a given rate we want to allocate bits to each subband in order to minimize the visual distortion The optimization problem leads to : Step size of the first band Step size of band b Visual weighing factor With : (see report)

12. PS221 project : pattern sensitivity and image compression Eric Setton - Winter 2002 Conclusion The Jpeg2000 uses the properties of the HVS It’s a good illustration of the first part But there are limits to this model : fixed viewing distance, the frequency is not constant in each band etc… This is why I liked this project : Impressive experiments Good understanding of Jpeg, Jpeg2000 I was taking the course to see how knowing about the HVS can help in image processing ! Developed new skills : Matlab GUIs, HTML