Patent ID: 6894666

Claim:
A contrast correcting circuit, comprising: an integrator for integrating brightness levels of received video signals, and for calculating a sum of the brightness levels of the video signals for an entire screen; a first memory for storing a plurality of different types of table data exhibiting contrast conversion characteristics according to a brightness of the screen; a selector for setting, as a reference value, a sum of the brightness levels of all pixels of the screen when the brightness levels of said all pixels of the screen are at a maximum, for comparing the reference value with an integration output of the integrator to produce a comparison result, and for instructing the first memory to selectively output table data suitable for the brightness of the screen selected from the plurality of different types of table data on the basis of the comparison result; a second memory for storing a conversion table for correcting contrasts of the received video signals by means of the table data output from the first memory; and a black level detector for detecting the brightness levels of the received video signals for each pixel, for determining the brightness levels of the video signals to be a black level when the brightness levels of the video signals have values no greater than a predetermined value, and for outputting data indicating a number of pixels of the black level, wherein, when the number of pixels of the black level indicated by the data output of the black level detector is no less than a certain value, the selector sets the reference value which is compared with the integration output of the integrator to a value obtained by subtracting the number of pixels of the black level from the sum of the brightness levels of said all pixels of the screen when the brightness levels of said all pixels of the screen are at a maximum.