| 摘要 |
PURPOSE:To obtain a picture having the optimum black and white gradations, by controlling the fall or the rise of the DC level that decides the luminance level of a luminance signal according to the presence or absence of a black signal and at the same time controlling the amplitude of the luminance signal. CONSTITUTION:The luminance signal supplied through a terminal 1 is fed to a DC reproducing circuit 3 via an amplifying circuit 2, and the DC component is reproduced to fix the black level. Furthermore the signal near the black level is detected by a black level detecting circui 4 and in the form of a black signal. This output of detection sets up and down the DC level of the luminance signal of the circuit 3 via a black level control circuit 5 and performs an automatic compensation for the fixed black level. At the same time, the black level is fed back to the circuit 2 via a luminance amplitude control circuit 11 that increases and decreases the amplitude of the luminance signal when the black level is detected by the circuit 4. Thus the white peak level is controlled to an optimum value by adding a feedback circuit to a conventional black level compensating circuit and in accodance with the change of the black level. As a result, a white or black picture is obtained with the good balance of gradation. |
