| 摘要 |
PURPOSE:To prevent a black imaging despite a white level, by varying the binary coding conversion level in response to the detection for deterioration of a fluorescent lamp. CONSTITUTION:When the distortions at both end parts increase owing to the deterioration of a fluorescent lamp, an output S5 is generated from a comparator 17 at the areas corresponding to the both end parts. As a result, an AND gate 22 is opened to set an FF23. Then a relay 16 is driven with conduction of a switching transistor 24 of a peak holding circuit 8, and a capacitor C2 is separated from a capacitor C1 when a relay contact 16' is opened. Therefore the capacity of a charging/discharging circuit 15 is reduced to decrease a timer constant. This accelerates discharging, and therefore the binary coding level is lowered to coincide with the shading distortion. The capacitor C1 is charged at and after this time point. Thus a binary coding circuit 10 does not decide a black level any more. As a result, the shading distortions of both end parts can be absorbed. |
