Some otherwise desirable liquid crystal materials have essentially no usable rotation range between off and on. This means that gray scaling can't be achieved by partial light transmission. Two techniques are used with these materials to obtain gray scale/brightness variation. Either subpixel elements are turned on or the length of time that the pixel is turned on is varied. Frame Rate Modulation does the later. Because LCDs have rather slow response, FRM works by omitting pixels from displays according to some pattern (e.g. every other frame or two frames on, one off). The eye averages the illumination, but flickering may a problem with some material if the frame rate is too low. Frame Rate Modulation can be used with either monochrome or color displays.
Return To Index Copyright 1994-2002 by Donald Kenney.