Adaptive spatial noise shaping for DCT based image compression

The most important visual artefacts that result from DCT based image compression are mosquito noise and blocking. Mosquito noise becomes visible due to the uniform spatial distribution of the quantization noise in blocks which contain textured as well as flat regions, which results in clearly visible noise in the flat regions. Spatial noise shaping is an encoder based technique which can be used to reduce mosquito noise by "hiding" the noise in that part of the block where it has the lowest visibility. We propose an efficient noise-shaping algorithm which gives accurate control of the spatial noise distribution. The encoder based technique is fully compatible with the JPEG and MPEG standards. Experiments show that noise shaping leads to a significant mosquito noise reduction.