GB1424410A - Methods of and systems for sharpness in the reproduction of continuous-tone pictures - Google Patents

Abstract

1424410 Facsimile DR-ING RUDOLF HELL GmbH 31 May 1973 [2 June 1972] 26071/73 Heading H4F In a facsimile system using an edge enhancement or sharpness signal, said signal is or is not added to the normal video signal in dependence on the pictorial content of the original picture; thus in a colour facsimile system flesh tones are left unsharpened, and/or areas of high contrast or detail are left unsharpened. A colour original 2, mounted on a rotating transparent drum 1 is spirally scanned by means of light source 12, and optics 13, 14, 18, 20, and the modulated light from the original is split into component colours by dichroic mirrors 23, 24 and photo-detectors, 25, 26, 27. The outputs of the photo-detectors are fed to a colour analyser 71 and also to a component selection switch 38 whereby a reproduction of a selected component may be produced photographically at 5 using modulated light source 41. A cathoderay tube 28 produces a circular scan image 30 which is used to scan an area of the original surrounding the spot 19 scanned by the main beam, and gives a voltage across capacitor 46 fed by photodetector 34, indicating the average brightness value of the scanned area. The difference between this average value and the brightness of the spot 19 gives a sharpness signal representation and is produced by differential amplifier 48 receiving the output of photo-detector 27 and the voltage across capacitor 46. The amount of detail in the area surrounding scanned spot 19 is given by the A.C. output of photo-detector 34 and is used via detector 58 to block transistor 50 passing the sharpness signal when the area is determined to be already detailed enough. If transistor 50 is not blocked, the sharpness signal proceeds to transistor 53 which is controlled by colour analyser 71. On detecting a combination of colour component amplitudes giving, e.g. a flesh tone, analyser 71 blocks transistor 53. If transistor 53 is not blocked, the sharpness signal is added to the component signal at the output of switch 38. A second sharpness signal is produced by double differentiation of the output of photo-detector 27 and is fed via transistor 91 for combination with the component signal. Transistor 91 is controlled by the detected output of photo-detector 94 which scans a mask 4 indicating areas 85 in which the sharpness signal is to be added. Transistor 91 is therefore enabled for these areas.