Journal of Electronic ImagingScanline algorithms in the JPEG discrete cosine transform compressed domain
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Scanline algorithms are popular in computer graphics for complex geometric manipulations. The main characteristic of scanline algorithms is that a geometric transformation is decomposed into multipass transforms with each pass operating only along row or column scanlines. This leads to conversion of 2-D image manipulation problems to straightforward 1-D problems resulting in simple and systematic methods. The goal of this work is to examine the scanline approach for manipulation of transform-compressed images without decompressing them. We show how the scanline algorithms for rotation and projective mapping can be developed for JPEG/DCT images. The performance of the proposed scanline algorithms is evaluated with respect to quality, speed, and control and memory overhead.