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Compression of aerial images for reduced-color devices

Compression of aerial images for reduced-color devices. Pasi Fränti and Ville Hautamäki. http://cs.joensuu.fi/pages/franti/comp/. UNIVERSITY OF JOENSUU DEPARTMENT OF COMPUTER SCIENCE FINLAND. Images in mobile navigation. L ocating the user by GPS or network.

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Compression of aerial images for reduced-color devices

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  1. Compression of aerial images for reduced-color devices Pasi Fränti and Ville Hautamäki http://cs.joensuu.fi/pages/franti/comp/ UNIVERSITY OF JOENSUU DEPARTMENT OF COMPUTER SCIENCE FINLAND

  2. Images in mobile navigation • Locating the user by GPS or network. • Location is shown in a meaningful context such as map or aerial image. • Compression for reducing the amount of data. • Number of colors limited.

  3. Methods in comparison Image types: • 8-bit (gray-scale) images • 2-bit images • 2-bit dithered images Compression methods:

  4. System diagram: two possibilities • Scheme 1: • Color quantization • Compression • Scheme 2: • Compression • Quantization after decompression

  5. Set of test images 600x450 Turku1 Turku2 Turku3 Turku4

  6. Visual examples 8-bit image 2-bit image 2-bit dithered

  7. Software used (All pages were still operational in 2002)

  8. Lossless compression 8-bit images Best result

  9. Lossy compression Images were originally compressed by JPEG once !!! JPEG-2000 better and steady 8-bit images Fractal compressor good with low bit rates

  10. Lossy versus lossless 8-bit images Lossy results selected as the lowest bit rates with visually lossless quality

  11. Visual comparison 8-bit images JPEG JPEG-2000 FIASCO

  12. Lossless comparison 2-bit images JBIG gives best results Dithering adds complexity to images

  13. Lossy versus lossless Lossless Lossy Visually lossless

  14. Visual comparison (1/2) 2-bit images JBIG (dithered) 1.34 bpp JPEG-2000 1.00 bpp JPEG-2000 0.25 bpp

  15. Visual comparison (2/2) 2-bit images JBIG (dithered) 1.58 bpp JPEG-2000 1.00 bpp JPEG-2000 0.25 bpp

  16. Conclusions • JPEG-2000 outperformed JPEG and FIASCO by wide margin. • In the case of 2-bit images, the following scheme is recommended: • Compress 8-bit image by JPEG-2000. • Color quantization after decompression.

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