1.3.3.2 Softproof

With electronic image signal processing the initially “analogue” scanners had at full automated the prepress reproduction as the end of 70ies with complete eliminating the use of cameras. They electronically solved the color correcting masking equations, similar to those previously used in photography, to transform the signals, taken from an original through RGB filters, to CMYK printing tone values. However, the multiple of potentiometers responsible for masking coefficients on the control panel of a scanner were governed by an operator due to his experience, intuition… and the need for some intermediate image copy - proof which could simulate the resulting print color was urgent. That’s why there was in those years developed the equipment electronically simulating the effect of prepress settings on the printing result (Figure 1.9).

Figure 1.9 Operator sets the color masking coefficients on control console of Chromograph scanner with placing an original in front of TV pick-up camera in one of the first soft proof systems Chromascope of Hell (1974).

Operator was able to view the model of the future print – softproof on color TV monitor. In the absence of digital memory for the full screen this equipment had to use the pick-up TV camera thus comprising the local, single frame color TV system. This function is nowadays provided by the calibrated and profiled DTP monitor.

1.3.3.3 Image scaling

It was no problem for image size continuous variation by smooth lens move in a camera. That allowed for direct obtaining the halftone transparency of desired dimension with the film exposure through a projection or a contact screen. However, it had occurred rather difficult in analogue drum scanners to vary the image size in circumferential direction.

The use of a few drums of different diameter allowed for just several steps of reducing or enlarging. That’s why, among the multiple of other patented proposals, the “swaying frame” carrying an original (slide) was over ten years used instead of a transparent scan drum.

Speed of back and force movement was set for said frame by regulating the arms length relationship of a lever connected with the film exposure drum rotation as shown in figure 1.10. The inertia of such mechanics couldn’t, however, provide the recording speed over 240 lines per minute which has greatly lowered the scanner operation.

Figure 1.10. Slide fixed on the swaying frame connected by lever gear with the recording drum of a scanner for copy size variation in circumferential direction.

This problem was cardinally solved when it became possible to put in a buffer memory the digitized signal of one scan line and to output it for recording at the following drum revolution. The length of recorded line was controlled by varying the clock frequency of analogue to digital transform at signal input to a buffer.

Such system was licensed from Dr. Ing. R. Hell company by Crosfield Electronics to implement it in scanner named Magnascan in 1970 [1.5].

The solution passing over Hell patent was later on realized by Dainippon Screen in its Scanagraph 701 [1.6]. Circumferential image size depended there on the speed of a scan drum rotation and the buffer was used just for control the starting moment of recording a line on the output drum without the signal frequency spectra transform. It has made for this purpose to divide the input and output drums which were earlier used to be fixed on the same shaft. As result, there was created the modular kind of a reproduction system comprised of the separate input and output units, i.e. of a scanner and imagesetter in modern terminology. According its purpose the latter can, in its turn, appear as filmsetter, platesetter, proofsetter, etc.