YIQ vector quantization in a new color palette architecture

Abstract

Many CRT displays use color palettes to save highspeed frame buffer memory and to support many interactive, real-time graphics and imaging operations. Existing quantization algorithms for color palettes cluster colors as 3-D vectors in a color space. Thus, they fail to remove the statistical redundancy in the image space. This weakness prevents a more efficient use of frame buffer capacity. We propose a simple product vector quantization (VQ) technique for frame buffers that exploits redundancies in both image and color spaces. The new VQ technique can reduce the frame buffer use of a color image by half from the current algorithms with comparable image quality. The NTSC YIQ rather than RGB color space is used in our product VQ scheme. Consequently, we propose to modify the current architecture of the color palette to suit the proposed product VQ algorithm in the YIQ mode. The modified color palette is nearly ten times smaller than the current RGB palette and is more flexible. The improved space efficiency in both frame buffer and color palette is achieved while neither complicating the control or logic of the frame buffer architecture nor increasing computational complexity of color quantization.