APPARATUS FOR MEASURING IMAGE AREA

摘要

PURPOSE:To accurately measure even the area of an image covered with a transparent substance, by a method wherein a light detecting element permitting the permeation of only light having a polarization surface which crosses linearly polarized light incident to an image to be measured at right angles is provided between the image to be measured and a photoelectric conversion part and only the light parallel to the permeation axis of the light detecting element among reflected lights is received by the photoelectric conversion part. CONSTITUTION:The laser beam from linear polarization type laser 41 is converted to light having circular polarization while passed through a 1/4 wavelength plate 42 and the converted light is further converted to linearly polarized light again by a polarization element 43 to be reflected by a scanning mirror 25A and the reflected light is allowed to irradiate a printing plate 30 to scan the printing plate 30 in the X- and Y-directions thereof by a scanner 25B and the revolution of the scanning mirror 25A by a stepping motor 22. In this case, the polarization element 43 and the scanning mirror 25A are integrally revolved and the relative angle of the polarization surface of linearly polarized light after passing the polarization element 43 and the incident surface on the scanning mirror 25A is always constant at the arbitrary angular position of the revolution of the scanning mirror 25A to a Y-direction and the deflection surface and the incident surface of the irradiated light are always kept constant.