Increasing contrast resolution and decreasing spatial noise for liquid-crystal displays using digital dithering

Active-Matrix Liquid Crystal Displays (AM-LCD) are gradually replacing the Cathode Ray Tubes (CRT) in the radiology reading rooms. Results of some initial study seem to confirm the high hopes placed in LCDs. But they are still far from ideal. Like CRTs, LCDs generally possess a limited contrast resolution. On the other hand, they exhibit higher spatial noise than CRTs. These can interfere with clinical diagnosis and reduce the efficiency especially when there are subtle abnormalities presented in clinical images. The purpose of this paper is to explore ways to improve softcopy display of medical images through appropriate image processing techniques to compensate for LCD's contrast resolution and spatial noise. Two digital dithering operations (error diffusion) are applied to treat contrast resolution and spatial noise separately. For contrast resolution compensation, the processing is done in the perceptually linear domain, whereas for spatial noise compensation, the corresponding processing is done in the display output luminance domain. Some initial results indicate that the compensation algorithms discussed in this paper indeed help to increase the performance of LCDs.