Method for variable quantization in JPEG for improved perceptual quality

Nasir Memon, Daniel Tretter

Research output: Chapter in Book/Report/Conference proceedingChapter


One of the main limitations of the ubiquitous JPEG standard is the fact that visible artifacts can often appear in the decompressed image at moderate to high compression ratios. This is especially true for parts of the image containing graphics, text, or some other such synthesized component. Artifacts are also common in smooth regions and in image blocks containing a single dominant edge. One approach to deal with this problem is to change the `coarseness' of quantization as a function of image characteristics in the block being compressed. The latest extension of the JPEG standard, called JPEG Part-3, provides the necessary syntax for supporting this process by means of scale factors that can be used to uniformly vary the quantization step sizes on a block by block basis. However, the standard does not recommend any specific technique or algorithm for determining scale factors. This paper proposes a simple algorithm for computing scale factors for the quantization tables used in the JPEG compression standard. The algorithm classifies each image block according to its activity and type which index into look-up tables that provide the scale factor to be used for the block. The look-up tables are designed experimentally to yield perceptually lossless compression for the target device under consideration.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSociety of Photo-Optical Instrumentation Engineers
Number of pages11
StatePublished - 2000
EventImage and Video Communications and Processing 2000 - San Jose, CA, USA
Duration: Jan 25 2000Jan 28 2000


OtherImage and Video Communications and Processing 2000
CitySan Jose, CA, USA

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Condensed Matter Physics


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