Patent GB-1405614-A (GB)
Title: Method of and apparatus for recognising colours
IPC: G03F3/08
Filed: 1972-08-10
Abstract: 1405614 Photo-electric identification of colour FRANZ MORAT GmbH 10 Aug 1972 [18 Aug 1971] 37433/72 Heading G1 [Also in Division H4] Coloured areas are analyzed photo-electrically by scanning the areas to develop a signal for each area whose amplitude variations with respect to time represent a spectral distribution for the area. By, for example, differentiating this signal, pulses may be formed whose time position represents the presence of a particular colour in the particular area. A variety of methods are disclosed for effectively dispersing the colours in an area, and for scanning the field. In Fig. 1, light is directed to image member 1 and only one of a plurality of colour dots illuminated at any one time. The reflected light is collinated at 7 and applied to as varying thickness interference filter 9 which effectively splits up the colours into separate lines, The filter 9 is scanned by a T.V. camera. A signal such as 13, Fig. 2 would be developed in the case of a single colour in a colour dot. In Fig. 5 (not shown), the image member 1 is illuminated via a narrow region of the interference filter, which is progressively moved through the beam. The reflected light is detected by a fixed detector (87). Alternatively, a rotating light beam scans across the filter and the light passing through is directed to the image member 1. In Fig. 6 (not shown), a refracting prism (89) or a diffraction grating replaces the filter in Fig. 1. The dispersed light from the prism is focused on to a ground glass screen which is scanned by a T.V. camera. In Fig. 7 (not shown), a rotating mirror drum is used to scan the light reflected from the image member across the interference filter, behind which is located a detector. In Fig. 8 (not shown), light from the image member passes through a rotating variable interference filter disc behind which is the detector. Alternatively, the detector is inside a cylindrical variable inteference filter. In Fig. 10, (not shown), polarized light produced by a polarizer (97) is reflected by the image member 1 and passed via an optical ferro-electric member (99) and an analyzer (101) to a detector. The voltage applied to the ferro-electric member is charged so as to charge the wavelength of the polarized light and effect a time varying spectral transmissivity. Apparatus for processing the video output from Fig. 1 is described with reference to Figs. 1 and 3. The camera output is differentiated at 19 and used to generate a pulse from device 23 which is used to produce a pulse at 33 representing the time of occurrence of a maximum signal. Circuit 25-29 is to cut out interfering short duration pulses. To determine which time section t 1  to t 6  the maximum has occurred in, the circuit of Fig. 3 comparing monostable 37, NAND gates 35, flipflops 41 and NAND gates 45, is used. This develops a O on one or more outputs F1-F6, representing the presence of one or more colours. Black and white are indicated at S and W. By adding the circuit of Fig. 4 (not shown), to the arrangement of Figs. 1 and 3, a column of dots may be examined simultaneously. The column is projected on to the interference filter to appear as a plurality of horizontal bands, the T.V. camera being operated so that a certain number of line scans are allocated to each horizontal band of the filter. The control output may be for a sorting, printing or textile machine.