Writable cholesteric liquid crystal display (ChLCD) and the algorithm used to detect its image were developed. A hard tip such as the fingertip could be used to draw an image onto the surface of ChLCD. Two states i.e., focal conic state (dark state) as F-state, and planar state (bright state) as P-state were designated in this paper. F-state or P-state could be detected by measuring the capacitance of one pixel of test cell (12 mm times 15 mm/1 times 1). However, it could not be detected using the same method on a 4.1" ChLCD (241 mum times 241 mum/320 times 320) due to the effect of parasitic capacitance. The reason why we measured capacitances and detected F-state or P-state was to look for a method which could be applied to detect the drawn image on ChLCD. By using a writable ChLCD, a user should be able to draw an image on it, and then detect and save the drawn image. Therefore, the high frequency measurement and the algorithm were developed to detect the image on ChLCD. Moreover, color writable ChLCD was also introduced.
