A Codebook Design Technique for Better Image Quality in Vector Quantization

Basically, our approach characterizes a pattern into a key value, which is used in codebook search. The key value is generated using a centroid method for each vector (block). It represents the angle of a line where the pixel values in the block are distributed with respect to. If the key value is equal to 45 degrees, it implies that the values of the pixels in a block are symmetrically distributed with respect to the diagonal line. “Reflection operation” with respect to diagonal line was performed on codewords using the key values to get more patterns to improve image quality. An extra bit is needed to indicate the reflection operation. Our basic VQ system is a 2-step VQ where VQ is used to compress prediction errors resulting from simple scalar quantization of pixel blocks. The codebook is a sorted list, which is sorted by pattern key values. The search strategy is :