SCANLINE ALGORITHMS IN THE JPEG DISCRETE COSINE TRANSFORM COMPRESSED DOMAIN

Scanline algorithms are popular in computer graphics for complex geome tric manipulations. The main characteristic of scanline algorithms is that a geometric transformation is decomposed into multipass transform s with each pass operating only along row or column scanlines. This le ads to conversion of 2-D image manipulation problems to straightforwar d I-D problems resulting in simple and systematic methods. The goal of this work is to examine the scanline approach for manipulation of tra nsform-compressed images without decompressing them. We show how the s canline algorithms for rotation and projective mapping can be develope d for JPEG/DCT images. The performance of the proposed scanline algori thms is evaluated with respect to quality, speed, and control and memo ry overhead. (C) 1996 SPIE and IS&T.