Abstract
JPEG, an international standard for still-image compression, is a widely used technique for compressing natural images. Popularity of JPEG stems from its flexibility, reasonable compression rate and ease of implementation. In baseline and progressive modes of JPEG, transform coding based on 8 X 8 block discrete cosine transform (DCT) is used. At high compression ratios (i.e. low bit rates), however, JPEG typically causes blockiness in the reconstructed image. In this paper, we highlight key factors that limit baseline JPEG's performance at low bit rates. Simple modifications within the JPEG construct are studied to improve the overall quality of images at low bit rates. In addition, a multiresolution-like organization of the 2 X 2 block DCT coefficients is considered and is shown to represent the Haar-based subband/wavelet transform.
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