Patent GB-792968-A (GB)
Title: Improvements in or relating to image translating system
IPC: G03B27/73
Filed: 1955-06-06
Abstract: 792,968. Viewing by scanning. TECHNICOLOR MOTION PICTURE CORPORATION. June 6, 1955 [June 16, 1954; April 13, 1955], No. 16149/55. Class 40 (3). Signals representative of colour-image aspect photographic negatives are supplied to cathoderay tube colour-picture reproducing apparatus so as to produce a photographic type positive display via individual channels each of which included means for modifying the signals to compensate for the logarithmic relationship between the signals and the density of the negative and for the non-linear transfer characteristic of the cathode-ray tubes and each of which also includes means for varying the brightness and the contrast of the reproduced image the latter means being calibrated, respectively, in terms of the printing light values and of the contrast requirements of different positive film stock which may be employed for printing a positive image from the negatives by conventional photographic techniques. Fig. 1, shows one embodiment in which the colour aspect signals are generated by means of a " flying-spot " scanner 10 which, together with co-operating photo-electric cells 18, scans Red, Green and Blue colour separation negatives 14, the generated signals being supplied to respective identical channels via video preamplifiers 20. The output of each of the latter is then supplied, after clamping of the pedestal pulses (introduced during scanning retrace intervals) at 22, to a logarithmic amplifier 24 which compensates for the logarithmic relationship between the density of the appropriate negative and the signals generated by scanning the latter and provides a signal linearly related to the density. This signal is applied to a circuit 26 which clips the pedestals at adjustable levels determined by a control device 28 and thus controls the brightness of the reproduced image and the clipped signals are then supplied to a variable gain linear amplifier 30 the gain control unit 32 of which controls the contrast of the reproduced image. The output from amplifier 30 is then supplied to an amplifier 36 which has a characteristic such as to provide the relationship of input signal to screen brightness required by the picture reproducing tubes 42 to which the output of amplifier 36 is supplied via linear amplifier 38. In operation the control devices 28 and 32 are first calibrated in terms of the exposure time (or printing light intensity) and of the contrast requirements respectively for the different types of positive film stock likely to be employed for printing from the colour separation negatives. The control devices are then adjusted until the composite image produced by optically combining the component colour images from the three tubes 42 is judged to be correct (by visual inspection) and the settings of these devices then supplies information concerning the photographic requirements which the printing involves. Fig. 11 shows an alternative embodiment in which the brightness control devices 26, 28 of Fig. 1 are replaced by an attenuator 322 and (calibrated) control device 324 and the functions of amplifiers 24 and 36 of Fig. 1 performed by a single non-linear amplifier 328 the contrast control arrangement including amplifier 330 being similar to the arrangement including amplifier 30 of Fig. 1. In order to simulate the spectral overlap of the dyes (used in the positive stock) a network 350 which combines portion of the signal in each channel with the signal in each of the other channels is inserted between the amplifiers 328 and the amplifiers 330. Such a network may also be employed in the output circuits of the video amplifiers 30 of Fig. 1, and details of suitable network circuits are given with reference to Figs. 8, 10 and 12 (not shown). The colour aspect signals may be generated by scanning colour paper negatives using reflection techniques or they may be derived from signals recorded on magnetic tape.