GB1273360A - Color reproduction system - Google Patents

Abstract

1,273,360. Facsimile apparatus. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 1 May, 1969 [2 May, 1968; 14 May, 1968; 4 June, 1968 (5)], No. 22374/69. Heading H4F. [Also in Divisions G1 and G4] In a system for the reproduction of an original print by the subtractive or additive method of colour reproduction, the original is viewed photo-electrically to produce three primary colour signals and various colour corrections are carried out on these signals before reproduction is carried out. The photo-electric detector circuit includes means to chop the detector outputs and to increase the S/N ratio. Light transmitted through or reflected by the original 1 is directed through a slit 7 to a three-part dichroic prism arrangement 8 having two dichroic planes 9, 10 by which green, blue and red light are directed via colour fillers 11 to photomultipliers 12 G , 12 B and 12 R respectively Fig. 2C (not shown). The resultant electric signals are passed through substantially identical colour correction channels. Considering the red channel only, the signal is initially chopped in circuit 13 R and amplified by circuit 14 R . After rectification in 15 R , the signal is rendered logarithmic by circuit 16 R so that colour correction operations may be performed The first two corrections are for γ (contrast) and highlight level and are performed by circuits 17 R , 18 R . In the masking circuit 19, in which signals from all three channels are combined, errors in the signals due to defects in the dichroic system, filters, sensitive materials used in reproduction, printing ink colours, &c., are removed. The operation involved for the red channel is subtraction of voltages derived from the green and blue channels from the red signal. In under colour removal (UCR) circuit 20 R , the amount of black in the red signal above a predetermined level set by circuit 202 is subtracted from the signal. The output of 20 R is amplified in 21 R and a selected colour channel output can be passed through anti-logarithmic circuit 22 to derived a printing (exposure signal. A black print signal may also be fed to anti-logarithmic circuit 22 being derived from the marking circuit 19 and being connected by its own highlight, γ and UCR circuits. The various circuits are detailed in Figs. 2a and 3-10 (not shown) with explanatory diagrams. The photomultiplier circuit, Fig. 2a (not shown), includes an astable multivibrator, (13a) generating a pulse waveform which is differentiated before supplying flip-flop (13b) which supplies the photomultiplier final dynode (39). Cancellation of induced noise is by applying a further rectangular wave to the anode through a capacitance (Co).