COLOUR AND BRIGHTNESS TRACKING IN A CATHODE RAY TUBE DISPLAY SYSTEM

摘要

A colour cathode ray tube display apparatus particularly for use under a wide range of ambient light conditions, such as in an aircraft cockpit, wherein each of the primary colour phosphors has a unique brightness versus cathode drive characteristic, which characteristic also is dependent upon whether the displayed information is raster written or stroke written, and wherein such characteristics also may vary from tube to tube. The output of at least one cockpit ambient light sensor (31) in addition to a pilot selected brightness (30) is used on a continuous basis to calculate a reference brightness level for the sensed ambient brightness conditions and display writing mode, this reference brightness level being used to calculate the corresponding brightness level for each of the primary colour components of the commanded symbology colour and concomitant drive voltages to the CRT cathode or cathodes. The operation and ambient brightness calculations are preferably performed by a microprocessor (26) and associated personality PROM (27) containing the colour/brightness characteristics of the particular cathode ray tube to which it is dedicated. The computations used are preferably logarithmic as is the data, whereby not only to simplify calculations but more importantly to correspond to the normal logarithmic reception characteristics of the human eye.