| 摘要 |
PURPOSE:To obtain a good transfer image by correcting irregularities in photographic printing density, by adding a differential element to a system for detecting and correcting irregularities in photographic printing density caused by irregular resistance values of the heat generating elements of a photographic printing apparatus having a thermal head having a predetermined number of heat generating elements arranged thereto in a line. CONSTITUTION:The power source voltage of the input terminal 5 of a thermal head driving power source is supplied to the prdetermined heat generating element of a thermal head 2 through a reference resistor R1. This reference resistor R1 is connected to a switch S1 in parallel and the connection point of the reference resistor R1 and the thermal head 2 is connected to the non-reversal input terminal of an operator amplifier A through a differential circuit to which a condenser C1 and a resistor R2 are connected in series. In addition, one terminal of a variable resistor R3 is connected to a bias power source terminal B while the other terminal thereof is grounded and a movable element is connected to the non-reversal input terminal of the operator amplifier A. Further, a resistor R4 is connected between the non- reversal input terminal of the operator amplifier A and the non-reversal input terminal of the operator amplifier A is grounded. In addition, the output terminal of the operator amplifier A is connected to the input terminal of an analogue-digital converter 5 through a resistor R5 and a differential element is added by the condenser C1 and the resistor R2 to correct photographic printing data. |
