Vision Group @ NASA Ames

The visibility of DCT quantization noise (1993)

Many standard image compression techniques apply the Discrete Cosine Transform (DCT) to the image, then quantize the resulting transform coefficients. For optimal compression, the DCT coefficients should be quantized as coarsely as possible, while allowing minimal visible distortion in the decompressed image. Quantization of a DCT coefficient induces a noise pat- tern over the image consisting of random amplitude replications of the corresponding basis function. Here we measure the detectability of such noise patterns for three different size test patterns. Implications of the experimental results are discussed. These measurements will facilitate the design of visually optimized DCT coefficient quantization schemes.