Constant light greyscale generator for CRT color camera system
AssigneePolaroid Corporation
InventorLawrence E. Alston
Life of this patent
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Abstract
A hard copy of a video frame represented by periodic video signals is obtained by dividing the range of amplitude of the video signals into N levels, converting the video signals into N two-level brightness distributions on the screen of a monochromatic CRT under the condition that a pixel in the ith distribution has the upper of two levels only if the level of the video signal representing the corresponding pixel in the frame exceeds the ith level, and exposing a photosensitive sheet to light from the screen. Thus, each pixel on the sheet is exposed to light of predetermined brightness for a period of time functionally dependent on the level of the video signal represented by the corresponding pixel in the frame.
Claims24
A method of obtaining a hard copy of a video frame represented by periodic video signals which lie within a predetermined range of amplitudes that define N levels of brightness comprising the steps of:
- comparing the amplitude of the video signals with a reference signal level to provide a select output signal when the amplitude of the video signals is at least equal to the amplitude of said reference signal;
- shifting the reference signal level through N levels corresponding to the N levels of brightness defined by the predetermined range of video signal amplitudes at a frequency functionally related to and synchronized with the periodic frequency of the video signals;
- deflecting a CRT in response to the sync signals in the video signals so as to cause the beam of the CRT to trace out a raster on the screen of the CRT and controlling the intensity of the beam to provide a two-level brightness distribution with the upper of said two levels of brightness occuring in response to said select output signal from said comparator;
- and
- exposing a sheet of photosensitive material to the screen of the CRT.
An apparatus for obtaining a hard copy of a video frame represented by a periodic video signal comprising:
- (a) a comparator having signal and reference inputs for producing an output when the signal applied to its signal input exceeds a threshold defined by the voltage applied to its reference input;
- (b) means for applying said video signal to the signal input of said comparator;
- (c) means for shifting said voltage applied to the reference input of said comparator at a frequency functionally related to and synchronized with the periodic frequency of the video signal;
- (d) a CRT having a deflection circuit responsive to the sync signal in the periodic video signal for causing the beam of the CRT to trace out a raster on the screen of the CRT, and having an intensity control responsive to the output of said comparator for controlling the intensity of the beam whereby a two-level brightness distribution is produced on the screen;
- and
- (e) means for stationing a sheet of photosensitive material for exposure to the screen of the CRT.
A method of obtaining a hard copy of a video frame represented by periodic video signals which lie within a predetermined range of amplitudes that define N levels of brightness comprising the steps of:
- comparing the amplitude of the video signals with a reference signal level to provide a select output signal when the amplitude of the video signals is at least equal to the amplitude of said reference signal;
- shifting the reference signal level through N levels corresponding to the N levels of brightness defined by the predetermined range of video signal amplitudes at a frequency functionally related to and synchronized with the periodic frequency of the video signals;
- controlling the intensity of a display screen to provide a two-level brightness distribution with the upper of said two levels of brightness occuring in response to said select output signal from said comparator;
- and
- exposing a sheet of photosensitive material to said display screen.
An apparatus for obtaining a hard copy of a video frame represented by a periodic video signal comprising:
- (a) a comparator having signal and reference inputs for producing an output when the signal applied to its signal input exceeds a threshold defined by the voltage applied to its reference input;
- (b) means for applying said video signal to the signal input of said comparator;
- (c) means for shifting said voltage applied to the reference input of said comparator at a frequency functionally related to and synchronized with the periodic frequency of the video signal;
- (d) a display screen;
- (e) an intensity control responsive to the output of said comparator for controlling the intensity of said display screen whereby a two-level brightness distribution is produced on said display screen;
- and
- (f) means for stationing a sheet of photosensitive material for exposure to said display screen.
Dependencies are inferred from the claim text.