Lossless compression of VQ index with search-order coding

In a memoryless vector quantization (VQ) for images, each block is quantized independently and its corresponding index is sent to the decoder. This paper presents a new lossless algorithm that exploits the interblock correlation in the index domain. We compare the current index with previous indices in a predefined search path, and then send the corresponding search order to the decoder. The new algorithm achieves significant reduction of hit rates without introducing extra coding distortion when compared to memoryless VQ’s. It is very simple and computationally efficient.