Abstract
This paper presents measurements of display function, spatial resolution (MTF), grayscale precision and spatial noise of three monochrome LCDs. Each of these LCDs features a different method to increase the grayscale precision: Frame Rate Modulation, Sub-Pixel Modulation and Aperture Modulation. A CCD camera was used for the evaluation. It imaged a small portion of the LCD, usually with over-sampling of between 115:1 and 8:1 CCD pixels per LCD pixel. The evaluated systems have image quality that in many respects is superior to CRT displays. Most impressive is the spatial resolution. The MTF of the systems investigated is almost unity. The typically 8 bits grayscale precision can be significantly increased by temporal as well as spatial modulation techniques. It appears that the aperture modulation technique alone can achieve a precision of 10.8 bits or 1800 distinct luminance levels. Spatial noise was evaluated in terms of single pixel signal-to-noise ratio and in terms of the spatial noise power spectrum. Single pixel signal-to-noise ratios for one LCDs were in the order of 100:1, and for another one the spatial noise power density of the normalized NPS at spatial frequencies below the LCD Nyquist frequency of 2.4 lp/mm was about 3.1E-5 mm2, values which are in the order of those from high performance CRTs.
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