PURPOSE: To measure a 100% level signal, without providing a calibration mark, by measuring the amount of reflected light from a printing plate by a probe sensor, which is independent of a scanning head.
CONSTITUTION: A probe sensor 19 is operated, and a total reflection area and a total absorbing area are measured. Then, a white level signal value and a black level signal value are obtained. In a printing plate, a part, whose printing area rate is 0% is measured, and a 0% level signal value is obtained. Then, a level signal value for a 100% printing area rate is obtained. Thereafter, the total reflecting area and the total absorbing area are scanned by a scanning head, and white level and black level signal values are obtained. The measured values of the sensor and the head are proportionally computed, and the level signal values at 0% and 100% for the head are obtained. Then, a PS plate is scanned by the scanning head, and the level signal value corresponding to the difference obtained by subtracting the 100% level signal value from the 0% level signal value for every light receiving element is obtained. Thus the printing area rate at the part where the head is scanning is obtained.
HOUKI TETSUO
KURUSU YASUO
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