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Problems with DCT-based compression

wavelets/subband coding. Problems with DCT-based compression Blocking artifacts, especially at low bitrate The methods for reducing blocking artifacts, such as overlapped transforms, are costly and complicated

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Problems with DCT-based compression

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  1. wavelets/subband coding • Problems with DCT-based compression • Blocking artifacts, especially at low bitrate • The methods for reducing blocking artifacts, such as overlapped transforms, are costly and complicated • Applying DCT on the whole image, rather than on small blocks, • ignores the significant differences in frequency contents in various regions of the image,thus leading to less quality-bitrate performance

  2. Advantages of wavelets / subband coding • They operate on the whole image as one single block, thus avoiding blocking artifactswhile dynamically adjusting the spatial/frequency resolution to the appropriate level • in various regions of the image • In practice, wavelets/subband coding performs as well as DCT and sometimes better, especially at low bitrate

  3. General Scheme

  4. Treelike Coder Treelike Decoder

  5. fy LH HH HH HL LL HL fx HH LH HH

  6. Lenna Original

  7. Subband Level 1

  8. Lenna Restored 1

  9. Subband Level 2

  10. Lenna Restored 2

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