Adaptive transform coding of still images

摘要

In accordance with our adaptive transform coding algorithm for a still image, the image is divided into small blocks of pixels and each block of pixels is transformed using an orthogonal transform such as a discrete cosine transform. The resulting transform coefficients are compressed and coded to form a bit stream for transmission to a remote receiver. The compression parameters for each block of pixels are chosen based on a busyness measure for the block such as the magnitude of the (K+1)th most significant transform coefficient. This enables busy blocks for which the human visual system is not sensitive to degradation to be transmitted at low bit rates while enabling other blocks for which the human visual system is sensitive to degradation to be transmitted at higher bit rates. Thus, the algorithm is able to achieve a tradeoff between image quality and bit rate.