Sequential vector quantization of directionally decomposed DCT coefficients

A new transform domain vector quantizer has been introduced for efficient image coding which employs directional decomposition and sequential vector quantization of DCT coefficients (DCT-SVQ): the DCT coefficients are decomposed into 16 slightly-overlapping subvectors for a subvector to convey key information about one directional image, and then the decomposed subvectors are vector quantized sequentially. The scheme has the capability of the rate control with no need for changing the codebooks and reveals good performance over a wide range of code rates. This paper addresses the improvement of that scheme by (1) adjusting the quantization step size of the DC quantizer as well as the AC quantizers according to the target distortion of the reconstructed image and (2) introducing the activity of an image block to the decision of the appropriate stopping condition of the sequential vector quantizer for that block