| 摘要 |
PURPOSE:To accurately measure the density of the printing on a medium. CONSTITUTION:An image forming optical system 3 condensing the reflected light from a medium 1 and the slit member 5 having an aperture part 4 narrower than the printing 2 on the medium and provided at the primary image forming position of the image forming optical system 3 are provided. Further, a photodetector 6 detecting the light passed through the aperture part 4 of the slit member 5, an amplifying circuit 7 amplifying the output of the photodetector 6 and a comparator 9 comparing the output value of the amplifying circuit 7 with the reference value from a reference power supply 8 are provided. |
