Transform coding of images using directionally adaptive vector quantization

An image coding technique is described that compresses monochrome digital TV images from 8 to about 1 bit/pixel while maintaining high quality. First, for subblocks of 8*8 pixels the discrete cosine transform is calculated. Then, the resulting block of 8*8 transform coefficients is divided into a number of subvectors, each of which is normalized and quantized using vector quantization. The subvector construction and the vector quantization are performed adaptively to the 'direction' of spatial activity in the pixel subblock. The quantization also adapts to the energy of the subvector.<<ETX>>