GB1244748A - Improvements relating to image reproduction equipment - Google Patents

Abstract

1,244,748. Image reproducing systems. CROSFIELD ELECTRONICS Ltd. 18 Nov., 1969 [26 Nov., 1968], No. 56087/68. Heading H4F. An image reproducing apparatus having means for scanning an original to derive sharp and unsharp signals substantially linearly related to density variations in the scanned original is provided with means for obtaining a fringe signal corresponding to density transitions in the original by differencing the sharp and unsharp signals, a non-linear amplifier to increase that portion of the fringe signal corresponding to the light side of each transition relative to that portion corresponding to the dark side of the transition, and means for adding the output of the non-linear amplifier to the sharp signal to produce a signal which is used to modulate a scanning exposure source. The non-linear amplifier corrects for unequal fringe component amplitudes said to occur in prior art systems. As shown, Fig. 1, in a single colour (red) channel in a colour scanner signals from a sharp photomultiplier 1 and from an unsharp photomultiplier 2 (having a larger amplitude) are applied to logarithmic amplifiers 3, 4, the resulting sharp signal is inverted by inverter 5 and together with the unsharp signal applied to a summing amplifier 6 provided with a non-linear feedback path 9 to produce a fringe signal having equal positive and negative amplitudes on either side of density transitions in the scanned original. A variable proportion of the fringe signal is then added to the sharp signal by amplifier 13. A suitable negative feedback network 9 incorporating a diode is described with reference to Fig. 3 (not shown).