Patent GB-1487754-A (GB)
Title: Method for preparing colour separation printing patterns
IPC: H04N1/62
Filed: 1974-09-30
Abstract: 1487754 Copying by scanning AGENCY OF INDUSTRIAL SCIENCE & TECHNOLOGY and DAIDO-MARUTA FINISHING CO Ltd 30 Sept 1974 [1 Oct 1973 28 Jan 1974] 42413/74 Heading H4F Red, green and blue colour component signals derived from a scanned multi-coloured original (1, Figs. 1, 2, not shown) are converted to digital form and combined to form a primary colour signal train, the amplitude of which indicates the detected colour, and this signal train may be recorded; the primary colour signal train is processed to correct for imperfections and defects in the original and to adapt it for the conditions of the final printing process, the resulting signal train being used to produce colour separation films. The primary colour signal train is read by a read-in unit 11 and the signals derived from the original picture are fed via a control unit 12 to a picture element register 13, and reference signals, derived from sample colours (3, Fig. 1, not shown) mounted alongside the original picture or from manually selected portions of the original picture, and representing all the colours in the original picture, are recorded in a sample colour register 15. Register 15 has previously had recorded therein data indicative of the original colours. When all the reference signals have been recorded in register 15, a colour processing circuit 14 processes the data recorded in each section of register 15 in relation to the data recorded in the other sections of register 15 and re-records the data in register 15. The outputs of picture element register 13 are successively fed to a change detection circuit 16 and compared with the previous picture element value stored in a register 17. If no change is detected the count of register 17 is advanced by one. If a change is detected the output of detection circuit 16 is passed to a processing circuit 18 including a number of series circuits 18 1 , 18 2 - 18 n  in which have been recorded respective conditions of change which may occur in the original picture. If the processing circuit 18 indicates that the change is due to a defect in the original picture and the data represents the same colour as before, the count in register 17 is advanced by one. If, however, the processing circuit 18 indicates that the change is due to a colour change, the stored value and count of register 17 are transferred to a register 19 and register 17 stores a code representing the change and a count of the number of picture elements for which the change lasts. Successive signals stored in register 19 and representing a single colour are transmitted to a colour identification circuit 20 which also receives inputs from sample colour register 15. Circuit 20 identifies the colours represented by the signals from register 19 and transmits to a pattern identification circuit 22 the colour code of the appropriate signal in register 15 together with the number of picture elements of this colour. Signals from register 19 representing changing colours are supplied to a processing circuit 21 where the signals are processed, e.g. by separating the signals of overlapping colours so that the first half of the picture elements are represented as one colour and the second half as the other colour, the processed signals being passed to pattern identification circuit 22. Circuit 22 interpolates the received signals with the use of a predetermined coefficient, and the resulting signals are recorded in a register 23. The signals recorded in register 23 are further processed by a circuit 24 to smooth pattern outlines and by a circuit 25 to provide all fine lines with a predetermined width. The resulting signals are fed to a circuit 26 which shifts the boundaries between colours towards the darker colour, the lighter colour being enlarged over the darker colour. The resulting signals are supplied to a circuit 27 which adds a fine line to each side of a background pattern, and thence to an interpolating circuit 28 and a printing pattern register 29. An output control circuit 30 separates the signals representing one colour which are supplied to a modulator 32 controlling the output of a laser 35 exposing a film on a drum 33.