| 摘要 |
1,183,419. Facsimile systems. R.C.A. CORPORATION. 20 Feb., 1968 [23 Feb., 1967], No. 8284/68. Heading H4F. To produce a line width modulated halftone image of a continuous tone image on a transparency 12, the transparency is scanned by a flying spot scanner 20, and the image signals generated by detector 38 are amplified 40 and modulated 48 by a carrier signal from generator 44, the carrier signal being phase shifted by + 45 degrees. The amplitude of the output modulated signal is a function of the amplitude of the image signal and hence the tone of the transparency. The modulated signal is used to vary the width of the scanlines on cathode-ray display tube 14 by adding it to the vertical deflection signal in sununing amplifier 58 and applying the summed output to the vertical deflection coil 60 of display tube 14. Capacitor 56 removes the D.C. component and limiter 57 limits the modulated signal so that alternations in one scanline do not overlap the alternations in adjacent scanlines on the face of tube 14. The scanning electron beam 62 has different velocities depending upon the portion of the alternating, e.g. sinewave, cycle the beam is traversing, and these differences in velocity produce unequal exposures on photographic film 16 which is exposed to the display tube face 14. To compensate for this intensity variation the image signals are modulated 66 by the carrier from generator 44 phase shifted by - 45 degrees so that the output wave is 90 degrees out of phase with the output of modulator 48. The output from modulator 66 is full wave rectified 70 and coupled to a summing amplifier 72 before being applied to the control grid of tube 14. Thus the compensation circuit 64 intensifies the scanning spot when the beam 62 is rapidly deflected and reduces the intensity when the beam is slowly deflected. A tone expander 80 is arranged to turn on the scanning beam 62 only when the image signal is above a predetermined threshold level, i.e. beam 62 is turned off when dark tones are scanned. Circuit 80 operates to expand the tone range up to a threshold level determined by diode 104, a threshold level being necessary to prevent highly deflected signals from being brighter than smaller deflected image signals. Instead of a raster scan in tube 14 a single line scan may be utilized, film 16 being moved. Stored signals from memory 110 may be displayed. Wavy line instead of straight line halftone image may be produced by coupling a low frequency oscillator 112 to amplifier 58 and to the flying spot scanner 20, and the resulting undulating scanlines may be broken at random to create a mezzo effect by applying the low frequency oscillations from oscillator 112 and an aperiodic wave from a noise generator 114 to a modulator 116. |
