JPH0446416B2 - - Google Patents

Description

Claim 1: A method for obtaining a hard copy of a video frame formed by a periodic video signal having an amplitude within a preset range defining N levels of brightness, comprising: (a) the video signal; comparing the amplitude of the video signal with the amplitude of the reference signal such that one selected output signal is generated when the amplitude of the video signal is equal to or greater than the amplitude of the reference signal; b) The level of the reference signal is set in N steps corresponding to N levels of brightness defined by a predetermined amplitude range of the video signal at a frequency related to and synchronized with the repetition frequency of the video signal. (c) deflecting the beam on the cathode ray tube in response to a synchronization signal in the video signal so that the electron beam draws a raster on the screen of the black and white cathode ray tube; (d) controlling the intensity of the beam so as to obtain a two-level brightness distribution, the upper level when the selected output signal is generated and the lower level at other times; (d) applying a sheet of photosensitive material; , exposing by the screen of the cathode ray tube.

2. In claim 1, the time for which the picture elements on the photosensitive sheet are exposed to the light of the higher level brightness distribution is determined by the amount of time that the picture elements on the photosensitive sheet are exposed to the light of the higher level brightness distribution. A method for obtaining a hard copy of said video frame, characterized in that it is a non-linear function of the amplitude of the signal.

3. In claim 2, the video signal forms a color-separated image of one frame, and the color of the light with which the photosensitive material is exposed matches the color of the color-separated image. A method of obtaining a hard copy of said video frames.

4. A method for obtaining a hard copy of a video frame according to claim 3, wherein a color hard copy is obtained by sequentially exposing the photosensitive material for each of the color separation images of red, blue and green.

5. A device for obtaining a hard copy of a video frame formed by a periodic video signal, wherein (a) the signal input to the signal input channel has a threshold value determined by the voltage applied to the reference signal input channel; (b) means for inputting the video signal to a signal input channel of the comparator; (c) related to and synchronized with the repetition frequency of the video signal; (d) means for changing the voltage applied to the reference signal input channel of the comparator at a frequency of a deflection circuit for drawing a raster on the screen of a cathode ray tube; and an intensity for controlling the intensity of the electron beam in response to the output of the comparator so as to obtain a two-level brightness distribution on the screen. (e) means for attaching a sheet-like photosensitive material so that it is exposed by the screen of the cathode ray tube;

6. In claim 5, the means for changing the voltage applied to the reference signal input channel of the comparator determines the voltage to each of a plurality of preset levels as a function of each level. Apparatus for obtaining a hard copy of said video frames, characterized in that said apparatus comprises means for setting and holding time intervals for said video frames.

7. According to claim 6, said means for setting and maintaining said voltage are such that each of said time intervals is determined as a non-linear function of said preset level associated therewith. A device that obtains a hard copy of a video frame.

8. In claim 7, the means for setting and holding the voltage comprises a level counter and a lookup table, the contents of the level counter representing one of the plurality of preset levels. , the lookup table comprises a plurality of cells addressed by the contents of the level counter, the contents of the cells representing the time during which the voltage is applied to the reference signal input channel of the comparator. Apparatus for obtaining a hard copy of said video frame.

9. In claim 8, the means for setting and holding the voltage includes a variable frequency divider circuit and a synchronous separation circuit, and the frequency divider circuit is configured to control the number of pulses input to a counter of the frequency divider circuit. is equal to the content of the cell addressed by the level counter, generates one output pulse in response to the content of the cell, and the synchronization separation circuit is responsive to the periodic video signal. to generate a series of frame pulses, the series of frame pulses being synchronized with the periodic video signal and input to the frequency dividing circuit. .

10. The apparatus for obtaining a hard copy of the video frame according to claim 9, wherein the level counter changes in response to the output of the frequency dividing circuit.

11. According to claim 9, said means for setting and holding said voltage generates a voltage representative of the contents of said level counter, said voltage being applied to a reference signal input channel of said comparator. Apparatus for obtaining a hard copy of said video frame.

12. According to claim 11, the means for setting and holding the voltage includes a synchronous counter that changes according to the output of the frequency divider circuit, and a D that generates the voltage in response to the contents of the synchronous counter.
- A device for obtaining a hard copy of said video frames, characterized in that it comprises an A converter.

13. The apparatus for obtaining a hard copy of the video frame according to claim 12, wherein the synchronization counter is separate from the level counter.

14. The apparatus for obtaining a hard copy of the video frame according to claim 12, further comprising means for stopping and resetting the level counter.

15. Apparatus according to claim 14, wherein said means for stopping and resetting is operative in response to the contents of said synchronization counter.

16. The apparatus for obtaining a hard copy of the video frame according to claim 15, wherein the stop and reset means further operates even when the video signal does not exceed a certain level.

TECHNICAL FIELD This invention relates to a method and apparatus for obtaining a hard copy of a visible image represented within a video frame (screen) by a plurality of periodic signals forming one video frame (screen). It is related to. In other words, the present invention uses a television cathode ray tube screen on which the same information is repeatedly displayed by a plurality of periodic video signals, in order to be able to obtain a color photograph of a color television image. This relates to taking photographs using the stop motion method to keep the image on the screen still.

BACKGROUND OF THE INVENTION One method of obtaining color hard copies of color television images is to photograph the screen of a cathode ray tube using color film. This requires a still image, which can be achieved by electronically selecting the video signal that forms the television screen and periodically inputting this signal to the color television's cathode ray tube. You can get it. Alternatively, the still image may be obtained by using a television camera photographing a still scene, or by using the output of a video disc or video tape recorder operating in stop-frame mode. It can therefore also be obtained by using images produced by a computer. Although these methods are effective for certain purposes, the image quality obtained by them is far inferior to that obtained by directly taking photographs of the scene to be broadcast. It is known from experience that this is a problem.

First, a color TV signal is divided into video signals separated into red, blue, and green, and then these signals are sequentially displayed on the cathode ray tube of a black-and-white television. The technique of photographing the screen through a filter of the same color as the video signal is well known. In this technology, a red color-separated image displayed on a black-and-white cathode ray tube screen is passed through a red filter for 50 seconds, a blue color-separated image is passed through a blue filter for 2 seconds, and a green color-separated image is displayed. Exposure to color film through a green filter for 6 seconds each is most commonly used. In other words, the film most often contains 1500 frames of red color separation, 60
A frame of blue color separation and a 180 frame green color separation are exposed. This exposure time naturally varies depending on the optical system, the phosphor of the cathode ray tube, and the type of color film, so the optimal exposure time is determined by trial and error.

Although the quality of the images produced by the last-mentioned technique is improved over that obtained by simply photographing a still image of a color video screen, the intensity of the light on the cathode ray tube is However, because it exhibits a nonlinear characteristic with respect to the level of the input signal, and because most film materials exhibit a nonlinear characteristic curve, the image quality is comparable to that obtained by directly photographing the scene being broadcast. The essential drawback is that images of similar quality cannot be obtained.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to obtain a hard copy of a video screen formed by periodic video signals, the quality of which is superior to that obtained by the known technique. The object of the present invention is to provide new and improved methods and apparatus for the invention.

DISCLOSURE OF THE INVENTION According to the present invention, each picture element on a photosensitive surface has a preset brightness for a certain period of time that is functionally dependent on the level of the video signal forming the corresponding picture element in the video screen. exposed by the light of This means that each pixel on the film is exposed for a preset period of time to light of a brightness that varies depending on the level of the video signal forming the corresponding pixel in the video frame. This is different from the conventional technology. In other words, the exposure of the pixel (i.e.
In the present invention, the product of the intensity of light incident on the picture element and the time that the light of that intensity is incident on the picture element is determined by changing the exposure time with light of a preset brightness. In contrast, in the conventional technology, it is determined by changing the brightness (intensity) of light. Because of this essential difference in exposure, in the present invention the characteristic curve of the film (i.e. HD curve or D-logE curve) is taken into account;
Image contrast is improved and photographs are obtained with image quality that more closely approximates that obtained by directly photographing the broadcast scene.

When the present invention is implemented, the region between the reference white and the reference black in the video signal is divided into seven levels, and the video frame is displayed on the screen of the cathode ray tube at least seven times. At each level, the video frame is displayed with a binary (ie, binary) brightness distribution. That is, if the amplitude of a picture element is greater than the selection level, the picture element on the screen will have a preset brightness, and conversely, if the amplitude is less than the selection level, the picture element on the screen will have a preset brightness. The picture element becomes darker. At each level, the total time that a frame is displayed is determined by taking into account the characteristic curve of the film. In this way, the actual video frame is
By decomposing the brightness distribution into N levels of binary brightness distributions on the screen of a cathode ray tube, and varying the time during which each distribution is displayed on the screen as a function of the characteristic curve of the film,
An improved photograph of the image on the screen is obtained.

Since the entire set of video signals forms one frame of a color-separated image, the color of the light that exposes the photosensitive surface must match the color of the color-separated image. In this case, by sequentially performing the above method on the red, blue, and green color separation images, a color hard copy of the color video screen is obtained. In each case, the film is exposed through a filter of the same color as the color separation image.

[Brief explanation of drawings]

FIG. 1 shows a television screen in which a plurality of vertical band-like patterns of uniform brightness are arranged in such a way that the brightness increases sequentially from left to right. FIG. 2 is an idealized representation of the video signals forming each row of the television screen shown in FIG. FIG. 3 schematically shows that the brightness distribution of a row of the screen shown in FIG. 1 can be decomposed into different levels. FIGS. 4A to 4H show that the television screen shown in FIG. 1 is adjusted according to each level shown in FIG.
This shows that it has a binary brightness distribution. FIG. 5 shows a typical characteristic curve when a certain photosensitive material is exposed to monochromatic light, that is, light of a certain predetermined wavelength. FIG. 6 is a normalized version of the characteristic curve shown in FIG. FIG. 7 is a table summarizing the changes in exposure required for each level to obtain images of various levels of brightness. FIG. 8 is a block diagram of an apparatus according to the invention for obtaining a color hard copy of a color video screen.

BEST MODE FOR CARRYING OUT THE INVENTION In order to fully understand the operation of the circuit shown in FIG. It is necessary to understand the entire background. In Figure 1,
Reference numeral 10 indicates a television monitor screen having picture elements arranged in a matrix of 8 rows and 8 columns, and the brightness of each picture element is indicated by the number attached to that picture element. ing. The number "0" indicates black, while the number "7" indicates the seventh level of the eight brightness levels. In other words, FIG. 1 shows that a plurality of vertical band-shaped patterns having uniform brightness are arranged so that the brightness increases sequentially from left to right.

When attempting to create such an image on a television screen using well-known technology, the video signals of each row are subject to periodic horizontal synchronization, as shown in a highly idealized form in Figure 2. pulse 11
In the area in between, the shape is almost step-like. When an electron beam scans the screen from left to right, from column A to column H, the intensity of the beam is
It is modulated according to the amplitude of the video signal shown in FIG. For example, since the video signal corresponding to the picture element in the Ath column of a certain row has no amplitude, it forms the reference black level. On the other hand, the video signal corresponding to the picture element in the H-th column is modulated to the seventh level of brightness, which is close to the reference white level.

In order for the image to appear static on the television screen, the video signal shown in Figure 2 needs to be input to the television over and over again, resulting in the image shown in Figure 1. As shown, a vertical strip pattern with different brightness is displayed. Generally, in order for the band-like pattern created on the screen to be perceived by the observer as a static image, one frame formed by the video signal is generated 30 times per second. It is created on the television screen. When taking a photo of the image on the television screen,
How many frames must be displayed on the screen in order to obtain sufficient exposure for the film is determined by a trial and error method. In such a case, the exposure time for each pixel on the film by the light from the screen is all equal, but the intensity of the light incident on the pixel formed on the film is different from the one that forms the corresponding pixel in the video frame. It changes according to the amplitude of the video signal being played. That is, in order to properly expose the picture elements in the fourth row of a television screen having seven different brightness units, a time of 10 seconds, or 300 frames, is required, for example. However, since each pixel on the film is exposed for the same amount of time, considering the characteristic curve of the film,
If picture elements in a column are properly exposed, it is highly unlikely that picture elements other than that column will be properly exposed.

In order to correct these drawbacks, the present invention adopts the concept shown in FIG. 3 and FIGS. 4A to 4H.

The video signal shown in FIG. 2 can in this case be decomposed into eight component parts, as shown in FIG. That is, the eight levels shown in FIG. 3, when superimposed on each other, reproduce the video signal shown in FIG. 2. If a level 1 video signal is input to the television screen, as shown in Figure 4A, the picture elements in column A have no brightness, and the pixels in column B to column The picture elements now have uniform brightness. As a result,
The left edge of the screen becomes a thin strip of black. Similarly,
When a level 2 video signal is input to the television monitor, the picture elements in the A-th and B-th columns become black, and the picture elements from the C-th column to the H-th column become uniform in brightness. In this way, if the video signal shown in FIG. 3 is used, eight two
A value (bin rank), ie, a binary brightness distribution is created.

The light coming from the television screen is the first
are synthesized on the film to reproduce the distribution shown in the figure. This can be seen in Figure 4.
For example, the total light amount of the pixels in the Hth column is 7,
This can be understood by noting that this is the value that the picture element in the Hth column shown in FIG. 1 has.

The method described above requires that the television monitor
It has the advantage of being constructed with an on-off type display, such as an LCD or LED type display. In other words, each picture element on the display is
It can be in either an on-off state, such as an off state when there is no light at all, and an on state when a preset amount of light is present. Using the concept shown in FIGS. 3 to 6, when exposing a film to light at each level, proper exposure can be obtained no matter what shape the film's characteristic curve has.

When the film is exposed to a preset level of light, the exposure time is determined such that curve 20 is formed. This curve 20 is called the film characteristic curve because the density of the film is a function of its exposure. Also, this curve 2
0 does not indicate an actual state, but a qualitative state. This is because such a curve is a function of both the dominant wavelength of light incident on the film and the properties of the film. In other words, in the case of color photography, a characteristic curve is created for each of the main colors red, blue and green, and the curve shown in Figure 5 is a variation of the curve so obtained. Either one is shown merely for explanatory purposes.

In preparation for determining exposure using a characteristic curve in order to obtain a hard copy from a video signal, the curve 20 is standardized to the reflectance shown in FIG. 5 and is calculated as shown in FIG. It will be redrawn.
That is, the maximum reflectance shown in FIG. 5 is 62.5% in this example, which is the reflectance in normalized units. Curve 30 shown in FIG.
is the normalized characteristic curve for a particular film and a particular color (wavelength). As shown in Figure 6, if this normalized reflectance is 8
Given that it is divided into step levels, the exposure time,
That is, the number of frames that must be captured on film for proper exposure at each level is determined by the portion of curve 30 that is cut by each level. The results can be summarized as shown in the table shown in FIG. That is, for example, it can be seen that approximately 90 frames are required to properly expose a picture element having a brightness level of "1". In addition, in order to properly expose picture elements with level "2" brightness, the total
140 frames are required, but 90 frames have already been exposed in order to expose the pixel with level 1 brightness, so requires only 50 frames. Thus, the right column of FIG. 7 shows the changes in the number of frames required at each level. This non-linear relationship between exposure time and each level is shown by the dashed line 31 in FIG.

In practice, when obtaining a color hard copy of a television picture, a set of curves as shown in FIGS. 5 and 6 is obtained for each of the major colors forming the color separation image. That is, a red video signal is input to the television monitor so as to produce light with a preset intensity, and this light is then incident on the film to create a characteristic curve for the red color separation image. be. This process is repeated for the blue and green color separation images, and as a result, three types of charts as shown in FIG. 7 are obtained. Here, the column on the right of each chart shows the amount of change in the number of frames required for each level of picture element to be exposed for each color of the color separation image.

An embodiment of the invention for obtaining a color hard copy of a video screen formed by three sets of red, blue and green color separation images is shown in FIG.

The video source 40 shown diagrammatically in FIG. 8 includes red, blue,
and green represent various video signal sources separated by color. What is important about this video source 40 is that
It generates video signals of the three color separation images, either simultaneously or sequentially, and this video signal is generated over and over again.
The multiplexer 42 receives the three color separated video signals and connects the three leads 44, 4 of the selector.
One of the three types of color separated video signals becomes the output of the multiplexer 42 depending on which one of the multiplexer 6 and 48 is activated.

The output of the multiplexer 42 is input to a signal channel 52 of a comparator 54 via a DC regeneration circuit 50, and the comparator inputs the video signal input to the signal channel to a reference channel 56 of the comparator. An output is generated if the applied voltage is greater than a threshold defined by the applied voltage. This reference voltage is D-A
The output of converter 58 is generated in the manner described below.

Comparator 54 operates to generate a signal as shown in FIG. 3 by dividing the video signal at a level determined by the output of DA converter 58. Comparator 54
generates one output only when the input value of the video signal is greater than the voltage set by the output of the DA converter 58. Such an output then acts on a controller 60 that controls the operation of the electron beam in the cathode ray tube of a black and white television. If there is no output from the comparator, the electron beam is not activated. By such a method, a binary brightness distribution is created on the cathode ray tube 62 according to the level set by the output of the DA converter 58 and the information in the video signal. It is created on the screen 64.

Light exiting screen 64 passes through one of the filters on filter disk 66 and then through lens 70 which is focused onto the film plane containing color film 72. It is possible to align the filter disk 66 in three positions so that one of the red, blue, or green filters is aligned on the optical axis of the lens 70. The rotation angle of the filter disk is controlled by a motor drive 7 controlled by a motor controller 76.
Adjusted by 4. and position sensor 78
detects the rotation angle of the filter disc, and
A control signal is generated that identifies a particular filter located on the optical axis of lens 70. As shown in FIG. 8, when the red filter 68 is aligned with the lens 70, the position sensor 78 generates an output signal on the lead 80 indicating this condition.
This signal on lead 80 is input to lead 44 which is connected to multiplexer 42, so that only the video signal of the red color separation image is input to DC component regeneration circuit 50. When the motor controller 76 operates the filter disk to align the blue filter with the lens 70, the position sensor 78 in turn generates an output signal on the lead 82, which signal
The blue video signal is input to the line 46 of the multiplexer 42, and as a result, only the blue video signal is input to the DC component regeneration circuit 50. Even when the green filter is located on the optical axis of the lens 70, only the green video signal is input to the DC component reproducing circuit 50 in the same way. In this way, the color of the video signal used to create the binary brightness distribution on the screen 64 of the cathode ray tube 62 matches the color of the filter located on the optical axis of the lens 70.

According to the invention, device 39 includes a level counter 84 whose output addresses a fixed memory 86 and whose output is a number "m". create.
Then, the frequency divider 88 divides the vertical deflection output 90 of the synchronous separation circuit 92 by the number "m",
This results in the level counter 84 and the synchronous counter 94 having the same content as the counter 84.
An output is generated to determine the amount of change in both.
The fixed storage device 86 constitutes a lookup table in which the information experimentally obtained from the characteristic curves shown in FIGS.
A list is provided for each of the video signals of the blue and green color separation images. If the right column of the table shown in Figure 7 is as shown in the table,
Let it represent the number of vertical frames required to get proper exposure at each level.
The contents of the right column of this table will represent the contents of fixed storage for the red color separation image.

Similarly, the input values to the lookup table for the blue and green color separation images are determined and the contents of persistent storage are configured. Level counter 84 addresses fixed storage according to each level, while the output of position sensor 78 determines whether the red, blue, or green content in fixed storage is to be processed. It has the function of selecting one. In conclusion, the contents of the level counter 84 and the selected filter on the filter disk 66 determine the cell of the fixed storage device, and the contents of that cell determine the number of frames that should appear on the screen of the cathode ray tube 62. do. This timing is achieved by using sync isolation circuit 92 and clock 88. The synchronous separation circuit is
A conventional device for acting on the video signal produced as the output of the multiplexer 42, the output 9 for horizontal deflection being input to the deflection coil 98 of the cathode ray tube.
6 and a vertical deflection output 90, the synchronization pulse is separated from the video signal.
The horizontal deflection output 96 is generally provided.
When the NTSC television system is used,
It is a pulse train with a frequency of 15750Hz, and this output is
The electron beam within the cathode ray tube 62 is deflected horizontally on its screen 64. The vertical deflection output 90 is a pulse train with a frequency of 60Hz, and in a system that does not perform interlaced scanning, as in this example, one field scan corresponds to one frame (screen).
Therefore, the 60Hz becomes the frame frequency. In this way, the electron beam in the cathode ray tube 62 draws a raster on the cathode ray tube screen 64 at a rate of 60 times per second.

Clock 88, controlled by selected cells in fixed memory 86, divides the vertical deflection pulses produced by sync separator circuit 92 into the following numbers: That is, the numerical value will be equal to the contents of the fixed storage cell addressed by the specific outputs of the level counter 84 and the position sensor 78, which specific outputs
It is determined by the color of the filter on the filter disk 66 that is in line with the lens 70. For example, if the content of the level counter 84 is the number "3", the video signal at level "3" is handled. Additionally, when the red filter is aligned with lens 70, the content of the cell addressed by level counter 84 and the "red" output on lead 80 becomes the number 50, and this number The result input to clock 88 is
One output pulse is generated every time the sync separation circuit 92 generates 50 vertical sync signals. The pulses generated as the output of clock 88 serve two purposes: first, to move synchronous counter 94 to the next level (i.e., level 4);
and secondly, to increment the level counter 84 to the next level. At this point, another cell in fixed storage is being addressed and clock 88 will therefore divide by the number contained in that cell.

The level determined by the contents of the synchronization counter 94 is converted into an analog signal by the DA converter 58, thereby setting the threshold of the comparator 54. As the level counter 94 increases, the threshold value in FIG.
The reference levels increase continuously, as indicated by numbers 1 through 8, but the time that the voltage is applied for each level is determined by the contents of fixed memory 86.

To explain the operation method, first, an unexposed sheet-like color film 72 is placed behind the lens 70 and on its focal plane. Video source 40 is operated to generate three sets of periodic video signals corresponding to the red, blue, and green color separations for a color television image. If the red filter is coaxial with the lens 70 and therefore the lead 80 of the position sensor 78 is activated, the multiplexer 42 will block the red filter formed by the set of periodic video signals. Generates output that creates video frames. This set of video signals is generated repeatedly until the lead 44 to the multiplexer is no longer active.

The video signal is applied to a signal input channel of a comparator 54 via a DC component regeneration circuit 50. The sync pulses are separated from the video signal by a sync separator circuit 92, which generates horizontal and vertical deflection outputs for a deflection circuit connected directly to the cathode ray tube 62. input channel 10
When a "start" command is input to clock 0, the contents of level counter 84, synchronization counter 94, and clock 88 are cleared. The "0" level of level counter 84 is then input to fixed storage 86, thereby addressing a row (horizontal column) of memory, while a column (vertical column) of memory is addressed by the output of position sensor 78. Since lead 80 is now active, lead 102 to fixed storage 86
A ``red'' signal is input to , which reads the contents of the level ``0'' cells in the selected column and determines the operation of clock 88. Then, when the divisor (number of divisions) for the vertical synchronizing pulse is determined, the clock 88
After the required number has been entered, the clock generates one output pulse to increment the synchronization counter 94 and level counter 84. While clock 88 is counting and before it generates an output pulse, D-
The A converter 58 receives the output of the synchronous counter 94 and applies a voltage corresponding to the "0" level to the reference input channel of the comparator 54. Each time the video signal input to the signal input channel of comparator 54 exceeds the threshold value applied to input channel 56 by the output of D-A converter 58, comparator 54 produces a single output for activating a light spot, which, for the entire frame, at a location on the screen 64 that corresponds to the location of the picture element in the video signal. In this way, the screen 64
Above, a black and white binary, ie, binary, brightness distribution is created that closely resembles any of the displays shown in FIGS. 4A to 4H. The display on the screen lasts for a fixed period of time determined by the contents of the addressed cell in permanent storage 86. Once this time has elapsed, the output generated by clock 88 changes the threshold voltage applied to comparator 54 while the output is applied to fixed memory 8 to set a new time.
6, specify a new address. Such a state is repeated until the level counter 84 and the synchronization counter 94 change to take on all values of permissible levels. At each level, a binary brightness distribution is displayed on the screen, and the display on the screen is exposed to the film through a filter whose color matches the color of the color-separated image.

The contents of the synchronization counter 94 are decoded so that when the contents reach a maximum value (i.e. maximum level), one output pulse is generated which activates the stop pulse generator 103, thereby causing the level counter 84 to The operation of the motor controller 76 is stopped, and a signal to activate the motor controller 76 is inputted to the motor controller 76. The motor 74 is driven in this manner and rotates the filter disk until the next color filter is positioned on the optical axis of the lens 70. The position of the filter disk is detected by the position sensor 78, and when the blue filter is positioned on the optical axis of the lens, the output to the lead 80 is stopped and, for example, The output to lead 82 is activated, and thus the output of multiplexer 42 changes from the red color separation image video signal to the blue color separation image video signal. At the same time, a blue color separation image is prepared to be exposed to the film when the start command is input.
Another column (vertical column) in permanent storage becomes active.

In response to another start signal, the above-described cycle is repeated once again for all levels, so that the binary brightness distribution for the blue color separation image is for each brightness level created on the screen 64. The exposure time for each level is determined according to the contents of the permanent storage. Once this exposure is complete, the cycle is repeated once more, thereby collecting the green color separation image information on the film 72. Three color separated images are sequentially formed on the screen 64, and the film 7
After the second exposure is completed, the film is developed and a hard copy of the video screen is created.

To quickly obtain a hard copy, a circuit schematically shown at 104 is used. This circuit operates to short circuit or terminate further operation of level counter 84 and synchronization counter 94 upon sensing when a level has reached a state where it no longer contains valid information. do. As shown in FIG. 8, flip-flop 106 is set as each frame is formed by vertical deflection pulses. If there is no output from the comparator 54 at a given level, that is, if no new information is included in the video signal because there is no pixel with an amplitude larger than the level in question, circuit 104
stops the operation of inputting the next color separation image to the film. In such a case, level counter 8
4 and synchronous counter 94, flip-flop 106 goes into the set state when the next clock pulse occurs. This pulse is then input to AND gate 108 while flip-flop 106 is in the set state.
As a result, AND gate 108 generates a so-called "initial stop signal" whereby clock 88 is stopped and circuit operation is stopped. However, if the video signal contains information related to intensity control, i.e., if the video signal has pixels with brightness levels greater than the threshold of comparator 54, flip-flop 106 is reset. The state will be as follows. Then,
When the next clock pulse corresponding to the next higher level occurs, AND gate 108 does not generate the initial stop signal and the voltage on the reference input channel to comparator 54 continues to increase stepwise.

Industrial Applicability As is clear from the foregoing description, the present invention provides a method for obtaining a hard copy of a video frame formed by a set of periodic video signals. Then, light of a preset brightness is used to illuminate each corresponding photosensitive surface on the photosensitive surface for a certain period of time determined by the level of the video signal forming the picture element in the frame. It includes a step of exposing the picture elements. As shown in FIG. 8, a level counter 84, a synchronous counter 94, a fixed storage device 86, a clock 88, and a D-A
Converter 58 constitutes a means for varying the reference voltage applied to the reference input channel to comparator 54. The level counter 84 and the synchronization counter 94 constitute means for setting the reference voltage. Fixed memory 86 then serves to hold the voltage constant at a predetermined level for a period of time varying as a function of the preset level in order to influence the operation of clock 88.

It should be noted here that level counter 84 and synchronization counter 94 can be combined as one counter. This is because the contents of each of these counters are always the same. However, for simplicity, two counters are shown here. These counters thus constitute means for varying the voltage applied to the reference input channel of the comparator at a frequency that varies as a function of the frame frequency of the television system and is synchronized.

It should also be noted that although an analog comparator and an analog video signal are described here, a digital video signal may be used in conjunction with a digital comparator including the comparator 54 and the D-A converter 58. This is easily understood.

Various advantages and improvements provided by the method and apparatus of the present invention will be apparent from the description of the preferred embodiment of the invention.
Within the spirit and scope of the invention as described in the following claims:
Various changes and modifications are permitted.