Optical information-processing apparatus and method

935,186. Spatial filters; photochromic material. NATIONAL CASH REGISTER CO. Oct. 11, 1960 [Oct. 12, 1959], No. 34776/60. Classes 97 (1) and 98 (2). A collimated visible light beam is diffracted by an object and focused on a filter which exhibits metachromism in response to radiation of which at least a major part of the spectrum lies outside the visible spectrum, means being provided for irradiating the filter with such radiation so as to modify the intensity of the visible light transmitted through the filter on to a light receiving device. In the system shown, visible light from screen S1 is collimated at L1 and focused by L2 on metachromic filter MCM2 so that on this filter is formed the image of source S1 as diffracted by an object OB (such as a transparency) which is imaged by L2 on a screen IPM. The image formed on IPM is modified by contracting the visible light transmissivity of the filter MCM2, this being done by irradiating selected areas of the filter with ultra-violet radiation from source S3 using a collimator L4 and semi-reflector BS1 and masks (not shown). The radiation from sources S1 and S2 are kept constant by radiation sampling and feed-back systems such as D1 and V.C.C. The filter MCM2 may be formed as a moving film or the metachromic material may be in film form deposited on slides or a long strip of quartz and be moved slowly or intermittently. Several examples of metachromic material are given. Specification 873,380 is referred to.