Patent GB-712499-A (GB)
Title: Improvements in electro-optical reproduction
IPC: H04N1/409
Filed: 1951-10-26
Abstract: 712,499. Copying by scanning. KODAK, Ltd. Oct. 26, 1951 [Oct. 27, 1950], No. 25040/51. Class 40 (3) In a method of electro-optical reproduction of an original subject, the latter is scanned sharply, with a scanning light point of elemental or picture point size, and unsharply, i.e. with a scanning point of larger size, substantially simultaneously, and the luminous responses corresponding to the two scanning operations are converted into electrical sharp and unsharp picture signals utilized to effect reproduction. The signals may be combined electrically to produce a resultant signal utilized to control a final light-emitting member to effect reproduction on a light-sensitive layer. Alternatively, the signals from the sharp and unsharp channels may control two lightvalves in tandem, Fig. 5 (not shown), or a glow discharge tube followed by a light-valve, Fig. 4 (not shown). The unsharp signals carry out electrically the process of masking-i.e. the result of printing from a sharp positive and an unsharp negative, or vice versa. Additionally as the masking effect or factor is of the same order as that required for the correction of one colour by another in three-colour and fourcolour processes, i.e. including a black printer, the masking operation may be used to effect simultaneous colour correction. In some cases it is found unnecessary to derive unsharp signals for all the colour components, and in other cases limited colour correction combined with the masking of the black printer is deemed to be sufficient. In the arrangement, Fig. 1, employing sharp and unsharp scanning for three-colour components and incorporating a black printer, the original transparency 11 is carried by a drum 10 rotated by a motor 16 and fed axially for scanning by a lead screw 18. A beam from a tight source 20 is chopped by a wheel 23 at a frequency higher than the picture point frequency and is reflected by a mirror 22 through the subject 11 to a beam splitter 25. One multiple beam passes to a small aperture 26 in an opaque plate 27 and via a lens 30 to reflectors 33RS. 33GS, 33BS and colour filters 34RS ... to three photo-electric cells 35RS.... Similarly the reflected multiple beam passes through a larger aperture 28 in an opaque plate 29 and via reflectors 33RU ... filters 34RU ... to photoelectric cells 35RU. ... The photo-cell outputs are passed through exponential amplifiers 36RS ... and 36RU ... allocated to the sharp and unsharp signals respectively. The outputs of the "unsharp amplifiers are fed to inverting rectifiers 37RU, 37GU, 37BU and the red signal is applied to mixers 38R, 38G. The green signal is fed to the blue mixer 38B, the output of the unit 37BU not being used in this embodiment. The maximum signal of the mixers 38R, 38G, 38B is selected by a black selector 39 and fed via amplifier 41X, rectifier 42X and light valve 43X to effect the printing of black on the sheet 15. A signal proportional to that applied to the black printer is fed through an inverting rectifier 45 to control mixers 40R, 40G, 40B whose outputs through light valves 43R, 43G, 43B control the yellow (Y), magenta (M) and cyan (C) printers 12, 13, 14 respectively. An arrangement, Fig. 2 (not shown), not arranged for colour reproduction, comprises a chopped light beam reflected through the transparency to a reflecting plate with a small aperture, the transmitted and reflected beams being associated with two separate photo-cells and constituting the sharp and unsharp scanning. The corresponding amplifier circuits are described in detail in connection with Fig. 3 (not shown). Alternative sharp and unsharp scanning arrangements include separate beams with associated reflectors within the drum and corresponding photo-electric cells, Fig. 6 (not shown), separate beams chopped at different frequencies applied to a single photo-electric cell whose output is applied to band-pass and lowpass filters providing the sharp and unsharp channels respectively, Fig. 7 (not shown), a single beam passed through a lens combination to provide sharp and out-of-focus spots at the transparency and inclined and annular mirrors within the drum to pick up the sharp and unsharp luminous responses, Fig. 8 (not shown). Other arrangements, Figs. 9, 10 (not shown) use differently polarized light beams and a polarizing beam splitter, such as that shown in U.S.A. Specification 2,403,731, to obtain separate beams corresponding to the sharp and unsharp scanning. A modification, Fig. 11, employs a single beam from a source 280 passing through a lens 281 and apertured plate 283 to be reflected*by mirror sections 286 for sharp scanning, and an out-of-focus mirror 291 for unsharp scanning, the beam being focused by a lens 287 on to an area 288 of the transparency. A beam from a second source 294 passes through an aperture plate 296 and the transparency or cut-away sections of the disc to a photo cell 297 controlling a switching relay 292 to alternate the output of the photo-cell 289 between the sharp and unsharp channels. Other arrangements using the switching of the sharp and unsharp signals comprise oppositely rotated discs with overlapping alternate large and small apertures, square or round, Fig. 12 (not shown), a disc with a ring of segments having alternate members of different polarization, Fig. 14 (not shown). A polarization device controlled magnetically to vary the size of the spot on the transparency with concomitant control of a relay to switch the output to the sharp and unsharp channels is shown in Fig. 13. Light from a source 320 passes through a polarizing screen 324 to an aperture 322 and is reflected to and from the surface 402 of an electromagnet 327 fed with current of a suitable frequency so that the plane of polarization of the light beam is variably rotated and by means of a bi-refracting lens element 325 sharp and unsharp spots are formed at the surface of the transparency 326. The frequency applied to the magnet 327 is also applied to a switching relay 329 for passing the output of the photo-electric cell 328 to the sharp and unsharp channels. A further arrangement comprises two ribbon light-valves, disposed at right angles and controlled by a square wave form of two distinct amplitudes to provide two square scanning spots of different sizes, the different amplitudes effecting the operation of the switching relay for the sharp and unsharp channels, Fig. 15 (not shown). Circuit modifications for colour correction and masking.-Figs. 18 to 23 (not shown) indicate modifications of the diagrammatic circuit arrangement of Fig. 17 which identically corresponds to Fig. 1. The modifications comprise an arrangement for masking each colour signal by its own colour and the black signal is masked in two stages in the separate colour channels and later in the black channel, Fig. 18 (not shown). Fig. 19 (not shown) is similar to Fig. 17 (not shown) or Fig. 1, except that the only unsharp signal is the red one and that the blue signal is masked by a sharp green signal, and Fig. 20 (not shown is identical with Fig. 19 (not shown) without the inclusion of the black printer. Fig. 21 (not shown) is identical with Fig. 17 (not shown) apart from the masking of the red signal by the unsharp red signal. Fig. 22 (not shown) is generally similar to Fig. 18 (not shown) except that the black selector receives its signals direct from the " sharp " colour amplifiers and that an unsharp black signal is obtained from the original transparency and utilized to mask the output of the black selector. In Fig. 23 (not shown) an unsharp black signal is set up in a signal selector, fed to an inverter rectifier and its output utilized to provide unsharp masking of the black signal and unsharp masking of the colour signals. Specifications 488,835, 517,265, 531,262, 538,012, 538,013, 538,661, 552,367, 561,844, 579,239, 592,270, 592,296 and 599,392 also are referred to.