| 摘要 |
PURPOSE:To measure a pattern area rate which is larger than constant accuracy by employing a specific density value which is stored previously as a black reference density value with a 100% area rate unless a black calibration mark is printed on a printing plate. CONSTITUTION:The blank part of the printing plate 1 is irradiated with a beam spot 5 from a laser light source 3 at a specific position. Its reflected light becomes an electric signal (density value signal) 6 corresponding to the quantity of the reflected light and is A/D-converted 7 and inputted to a CPU 8. Here, when the measured density value is larger than a specific threshold value, it is judged that the black calibration mark 9 is printed correctly on the printing plate 1, and the measured density value is employed as the black reference density value. Further, when the measured value is smaller than the threshold value, it is judged that the mark 9 is not printed and the specific density value which is stored previously is used as the black reference density value. Several stored values are prepared according to the kinds of the printing plates 1 and various conditions are inputted with keys before measuring operation. Thus, even if the mark 9 was inadoerteutly missed to be printed, the black reference value is settable, so the sufficient necessary measurement accuracy of the pattern area rate is secured. |
