| 摘要 |
PURPOSE:To increase sufficiently the contrast ratio of a white level and a black level of a reproduced picture by controlling the amplitude of a minute oscillation in response to the size of a spot of an electron beam changing attended with the rate of change in the lightness of the reproduced picture so as to compress the dynamic range of a detected output of a detecting means. CONSTITUTION:A wobbling signal Wob.S is applied to electrodes 21A, 21B of the 4th grid 21 so as to attain the amplitude modulation of a focus voltage thereby oscillating minutely an electron beam EB. base-emitter voltage of a transistor 71 is changed in response to a signal level of a luminance signal applied to the transistor 71 of a width adjusting circuit 70 in an oscillating means 27. Thus, the amplitude level of the electron beam is adjusted attended with the luminance change (change in the size of spot of electron beam) of the reproduced picture. Then, the dynamic range of the signal level of the luminance signal is increased without producing the oscillation or the like of a control loop, the contrast ratio of black and white levels of the reproducing picture is increased so as to sharpen the picture. |
