Abstract: In this paper, we report a novel heuristic for requantizing JPEG images. The resulting images are generally smaller and often have improved perceptual image quality over a blind requantization approach, that is, one that does not consider the properties of the quantization matrices. The heuristic is supported by a detailed mathematical treatment which incorporates the well-known Laplacian distribution of the AC discrete cosine transform (DCT) coefficients with an analysis of the error introduced by requantization. We note that the technique is applicable to any image compression method which employs discrete cosine transforms and quantization.

  author       = {Heinz H. Bauschke and Christopher H. Hamilton and Mason S. Macklem and Justin S. McMichael and Nicholas R. Swart},
  url          = {http://people.ok.ubc.ca/bauschke/Research/25.pdf},
  journal      = {IEEE Transactions on Image Processing},
  number       = {7},
  volume       = {12},
  year         = {2003},
  title        = {Recompression of {JPEG} images by requantization},
  pages        = {843--849},