GB1369702A - Image reproducing methods and apparatus - Google Patents

Abstract

1369702 Copying by scanning CROSFIELD ELECTRONICS Ltd 22 Dec 1972 [5 Jan 1972] 478/72 Heading H4F Colour facsimile apparatus includes a store 25 which provides output cyan, magenta, yellow and black signals corresponding to input red, green and blue signals, the relationship between the store input and output signals taking into account, e.g. compensations for the characteristics of the photomultipliers in analysing head 5 and the inks to be used in the final printing process, as well as editorial colour changes. The store 25 uses the input signals as address signals, the respective output signals being calculated, before scanning of an original, using a digital computer 24 fed with certain parameters from a control panel 29. For selection of the correct parameters analysing head 5 views a highlight, the parameters being then either manually adjusted, the values of the output signals being viewed in digital form on display 30, or adjusted automatically so that the highlight is set to the lowest printable ink level. An interpolator 26 is used for interpolation if the store input signals are not represented by an address in store 25. If the store input signals are seven-digit signals, the four most significant digits are used to address store 25, the three least significant digits being passed to interpolator 26 for linear interpolation using the eight store output values most closely corresponding to the input. A channel selector 27 then selects the colour (or black) which is to be used to produce a desired colour-separation. In an alternative embodiment (Fig. 6, not shown) the store 25 is split into two parts, one part being used to compensate for defects in the pick-up system, the resulting signals then being recorded on magnetic tape. The played-back signals are then passed to the second part of the store (or the first part which has had different output values fed into it by computer 24) for compensation of defects in the printing process, plus the production of the black level signal. A mask may be included scanned by a separate scanning head (66, Fig. 6, not shown), e.g. to be used in inserting lettering in the finished page. Pseudo-random numbers may be added to the signals before recording them on magnetictape, these numbers being subtracted from the played-back signals, thus giving a signal with more density levels.