Physical and psychophysical evaluation of LCD noise

Abstract

This paper presents the results of initial physical and psycho-physical evaluations of the noise of several high-resolution Liquid Crystal Displays (LCDs), which have different pixel structures. Spatial as well as temporal noise was physically measured with the aid of a high-performance CCD camera. Human contrast sensitivity in the presence of spatial noise was determined psycho-physically using square-wave patterns stimuli as well as square stimuli. The results demonstrate that spatial noise is the dominant noise in all LCDs, while temporal noise is insignificant and plays only a minor part. The magnitude of spatial noise of LCDs appears to be larger than that of Cathode Ray Tube (CRT) displays with a P104 phosphor. Of particular interest with respect to LCD noise is the contribution of the pixel structure to the Noise Power Spectrum, which shows up as sharp spikes at spatial frequencies beyond the LCDs' Nyquist frequency. Important is also the fact that spatial noise can be corrected for and essentially minimized. The process involved is called Error Diffusion. Spatial noise can almost be reduced by a factor of 2. Much more work is necessary to understand the impact of spatial noise on the diagnosis of malignant abnormalities like micro-calcifications.