BIT-LENGTH EXPANSION BY INVERSE QUANTIZATION PROCESS

Color bit-length (i.e., resolution of signal amplitude) is an important attribute to image quality. The bit-length is decided by the quantization of image capture devices. The precision in various image capture devices limits the color bit-length and introduces loss in visual quality. Expanding the bit-length is important image enhancement issue. For example, the bit-length expansion technique is necessity for the high-quality display such as the liquid crystal display (LCD) and the plasma display. Since, these displays have more the 10-bit resolution for each color component. However, in general, color image signals are defined by 8-bit resolution for each component. Moreover, the bit-length expansion technique is also necessary for low bit-length captured images. If we expand bit-length of these images by using most bit-length expanding algorithms, pseudo contouring effect is observed in smooth gradient area. The bit-length expansion process and inverse quantization process are equivalent. Inverse quantization is able to perform by suitable filtering. In this paper, the bit-length expansion method using a nonlinear filter with adaptive window size is proposed. We show the excellent bit-length expanded results are obtained by the proposed method.