U.S. patent number 3,854,005 [Application Number 05/346,723] was granted by the patent office on 1974-12-10 for film stabilizing system for electron beam recorder.
This patent grant is currently assigned to Columbia Broadcasting Systems, Inc.. Invention is credited to Robert A. Castrignano.
United States Patent |
3,854,005 |
Castrignano |
December 10, 1974 |
FILM STABILIZING SYSTEM FOR ELECTRON BEAM RECORDER
Abstract
The invention is applicable to an electron beam recording system
which includes a film transport for moving a film past a scanning
window, the system including an electron sensitive plate positioned
adjacent to the window, and means for scanning the modulated
electron beam in a repetitive scanline pattern over a reference
position which includes the plate and the window. In the system,
the rate of scanning is synchronized with the motion of the film
and the plate has an output which is a function of the intensity of
the beam that is incident on an active area thereof. The invention
comprises an improved subsystem for stabilizing the position of the
beam with respect to the film. In accordance with the invention,
there are provided interrupt means located at a prescribed position
on the plate for causing an interruption signal on the output of
the plate means when the electron beam is scanned over the
prescribed position. Means are provided for comparing the interrupt
signal to the timing of individual scanlines and for generating a
correction signal which reflects the comparison. Finally, means are
provided for varying the reference position of the scanline pattern
in accordance with the correction signal. In a preferred embodiment
of the invention, the interrupt means comprises a vertical slot in
the plate. In this embodiment, the interrupt signal is used to
sample a ramp voltage that is, in turn, synchronized with
horizontal synchronizing pulses. The sampled voltage is applied to
a sample and hold circuit which generates the correction signal for
application to the horizontal centering circuitry of the electron
beam scanner.
Inventors: |
Castrignano; Robert A.
(Stamford, CT) |
Assignee: |
Columbia Broadcasting Systems,
Inc. (New York, NY)
|
Family
ID: |
23360761 |
Appl.
No.: |
05/346,723 |
Filed: |
April 2, 1973 |
Current U.S.
Class: |
347/227;
386/E5.061 |
Current CPC
Class: |
H04N
5/84 (20130101) |
Current International
Class: |
H04N
5/84 (20060101); H04n 005/84 () |
Field of
Search: |
;178/6.7A,5.4M,5.2D,DIG.28,7.7 ;358/6,7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Konick; Bernard
Assistant Examiner: Faber; Alan
Attorney, Agent or Firm: Olson, Esq.; Spencer E. Novack,
Esq.; Martin
Claims
I claim:
1. In an electron beam recording system which includes a film
transport for moving a film past the scanning window; an electron
sensitive plate means positioned adjacent said window; and means
for scanning a modulated electron beam in a repetitive scanline
pattern over a reference position which includes said plate and
said window, the rate of said scanning being synchronized with the
motion of the film, the plate means having an output which is the
function of the intensity of the beam that is incident on an active
area thereof; an improved subsystem for stabilizing the position of
said beam with respect to said film, comprising:
interrupt means located at a prescribed position on said plate for
causing an interruption signal in the output of said plate means
when said electron beam is scanned over said prescribed
position;
means for comparing the timing of said interrupt signal to the
timing of individual scanlines and for generating a correction
signal which reflects the comparison; and
means for varying the reference position of said scanline pattern
in accordance with said correction signal.
2. The subsystem as defined in claim 1 wherein said interrupt means
comprises a slot in said plate.
3. The subsystem as defined in claim 1 wherein said interrupt means
comprises a vertical slot in said plate.
4. The subsystem as defined by claim 1 wherein said repetitive
scanline pattern is a horizontal scanline pattern synchronized by
horizontal synchronizing signals and wherein the timing of
interrupt signals is compared to the timing of horizontal
synchronizing signals.
5. The subsystem as defined by claim 4 wherein said comparing means
comprises:
a. means for generating a ramp voltage synchronized by said
horizontal synchronizing signals; and
b. sample and hold means responsive to said interrupt signal and
the ramp voltage output of said ramp generating means for sampling
and holding the value of said ramp at the time of occurrence of
said interrupt signal, the output of said sample and hold means
constituting said correction signal.
6. The subsystem as defined by claim 5 further comprising means for
activating said comparing means only during horizontal scanlines
which are scanning said plate.
7. The subsystem as defined by claim 6 wherein said correction
signal is applied to the horizontal reference control terminal of
the electron beam scanning means.
8. The subsystem as defined in claim 6 wherein said interrupt means
comprises a slot in said plate.
9. The subsystem as defined in claim 6 wherein said interrupt means
comprises a vertical slot in said plate.
Description
BACKGROUND OF THE INVENTION
This invention relates to the recording of data on a film and more
particularly, to an improved system for recording an image on
photographic film using an electron beam.
It is well known that information recorded in a succession of
frames on a photographic film can be scanned electronically such as
by a flying spot scanner to provide an electrical output signal
representative of scanned information and can be reproduced on a
display such as a television receiver. One system for recording
picture information on photographic film is known as electronic
video recording (EVR), wherein picture information is recorded in
successive frames and a television picture reproduced from this
film by means of electronic scanning and processing of resulting
video signals. Both monochrome and color pictures can be recorded
and reproduced by electronic video recording techniques.
In the case of monochrome pictures, the film contains a picture
track comprising a succession of photographic frames with a sound
track disposed along the film. For color recording, two picture
tracks are provided along the film, one track being a luminance
track comprising a succession of monochrome frames, the other track
being a color track containing frames of encoded chroma
information. In both monochrome and color recording, a
synchronization track is provided along the film and generally
includes an aperture in alignment with each frame from which
synchronization signals are derived. To reproduce or "play" the
recorded picture information, the recorded frames are each scanned
in a raster pattern compatible with a conventional television
receiver and a video signal generated to cause display of the
scanned picture on a television receiver.
In one version of the EVR player system, the film is scanned while
moving by a flying spot that follows the direction of the film
motion but at twice the film velocity. The vertical scan starts at
the top of a frame and at the end of one-sixtieth of a second
reaches the bottom of the frame. In this time the film moves one
frame and the scan moves a vertical distance equivalent to about
the height of two frames. During vertical blanking, the spot
returns to its original position to start the process over again on
the next film frame. This technique, as well as an overall
description of the EVR system, can be found in an article entitled
"Color EVR" which appeared in the September 1970 issue of IEEE
Spectrum.
Electron beam recording is found to be a particularly advantageous
technique for producing quality films in the EVR format. One
present production method involves a multimaster film which is 40mm
wide and includes four parallel masters, each master comprising a
frame track pair. After it is made, the multimaster film is copied
using a high speed printing technique and each copy thereof is slit
into four individual EVR films.
In recording a color EVR master, an NTSC color signal from a video
tape recorder is processed in two parallel channels, one for the
color signal and one for the luminance. After appropriate
processing, the EVR color and luminance signals are utilized to
respectively modulate the intensity of electron beams from a pair
of electron guns in an electron beam recorder. Generally, the
electron beam recorder consists of three chambers: one for the film
magazine, one for the film drive, and the third for the electron
guns and beams. To insure satisfactory beam focus and cathode life,
the electron gun chamber is maintained at a pressure of
approximately 10.sup..sup.-7 atmosphere. The film tends to be moist
and give off vapor, so the vacuum in the film chamber is poorer;
e.g., 10.sup..sup.-4 atmosphere. The film is exposed to the beams
through a small window or aperture and is kept as small as possible
to facilitate maintenance of the gun chamber at the substantially
lower pressure. Typically, the window is slightly larger than the
width of two side-by-side frames and has a height which corresponds
to the height of two frames. The two electron guns simultaneously
scan the film moving past the window. The horizontal scan rate is
the standard TV horizontal rate of 15,750 Hz. The film moves
vertically through the chamber at about six inches per second, or
60 frames per second; the beam's vertical scan rate being 12 inches
per second. The recording scan is similar to the above-described
scan used in playing developed film. Each beam begins scanning at
the top of the frame and by the time that frame has moved the
distance above one frame height, about 0.1 inch, the beam has
reached the bottom of the frame. A short blanking period occurs and
the beams fly back to the top of the next pair of side-by-side
frames.
As above stated, the film in the electron beam recorder is 40mm
wide and ultimately contains four separate and parallel two-track
masters. The gun chamber sits on a pair of trunnions and can be
indexed to five distinct horizontal positions; i.e., one position
known as the "monoscope" position, and the four positions
corresponding to the four frame track pairs. In practice the
chamber is first indexed at the monoscope position where a
specially designed monoscope target allows adjustment of the beam
parameters such as focus and scan dimensions. The monoscope is an
electron beam-sensitive semiconductor target which is provided with
a precise grid pattern that allows an accurate optical display of
the pattern which the electron beam is scanning and can thus be
used to achieve the type of adjustments just listed. After
appropriate adjustments at the monoscope position, the gun chamber
is indexed to a horizontal position on the film that is to be
occupied by the first of the two-track masters; i.e., the window is
moved horizontally to the desired position on the film. The master
is then recorded by advancing the film and activating the two
electron guns which simultaneously record the side by side
luminance and chrominance frames of the first master. The film is
then rewound and the gun chamber is moved over to the second
indexing position so that the window is now at a position on the
film where the second two-track master is to be recorded. The
second master is then recorded and the procedure followed two more
times to complete a 40mm multimaster film.
During the recording just described a technique is employed for
continually monitoring and automatically adjusting the gain of the
two electron beams. This technique employs a pair of special
plates, known as "VIT plates" which are located just above the
window and over the positions of the two side-by-side frame tracks
being recorded. The letters "VIT" stand for "vertical interval
test" and are appropriate since the electron beam raster scans are
preadjusted to impinge upon the plates during the vertical blanking
intervals which occur between fields of video information. Test
signals inserted in the blanking intervals modulate the electron
beams in a prescribed fashion. The plates are formed of a material
such as molybdenum which acts as an anode, so signals from output
conductors coupled to the plates indicate the instantaneous
intensities of the electron beams. These outputs are received by
automatic gain control circuits which regulate the gain level of
the electron guns.
The use of the described monoscope and VIT correction techniques
effectively minimize some of the problems associated with achieving
an accurate electron beam scan and film exposure level. However,
there remains a problem of maintaining an accurate registration
reference as between the raster scan and the film at the different
indexing positions of the gun chamber. Stated another way, when the
window has been moved to one of the four indexing positions on the
film, there is no way of knowing exactly where the beam will expose
the film. For example, a stray magnetic field may shift the raster
reference slightly to the left or right of the intended position on
the film. Magnetized metal parts in or near the chamber may have
this effect and the film copies ultimately made from an improperly
registered multimaster will have frames which are off center and
which reproduce with the loss of video at one edge.
Accordingly, it is an object of the present invention to provide a
subsystem for stabilizing the position of the electron beam in an
apparatus of the type described.
SUMMARY OF THE INVENTION
The present invention is applicable to an electron beam recording
system which includes a film transport for moving a film past a
scanning window, the system including an electron sensitive plate
positioned adjacent the window, and means for scanning the
modulated electron beam in a repetitive scanline pattern over a
reference position which includes the plate and the window. In the
system, the rate of scanning is synchronized with the motion of the
film and the plate has an output which is a function of the
intensity of the beam that is incident on an active area thereof.
The invention comprises an improved subsystem for stabilizing the
position of the beam with respect to the film.
In accordance with the invention, there are provided interrupt
means located at a prescribed position on the plate for causing an
interruption signal on the output of the plate means when the
electron beam is scanned over the prescribed position. Means are
provided for comparing the timing of the interrupt signal to the
timing of individual scanlines and for generating a correction
signal which reflects the comparison. Finally, means are provided
for varying the reference position of the scanline pattern in
accordance with the correction signal.
In a preferred embodiment of the invention, the interrupt means
comprises a vertical slot in the plate. In this embodiment, the
interrupt signal is used to sample a ramp voltage that is, in turn,
synchronized with horizontal synchronizing pulses. The sample
voltage is applied to a sample and hold circuit which generates the
correction signal for application to the horizontal centering
circuitry of the electron beam scanner.
Further features and advantages of the invention will become more
readily apparent from the following detailed description when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary view of a typical film format of the type
which can be produced using the present invention;
FIG. 2 is a simplified diagram of portions of an electron beam
recorder and associated circuitry suitable for producing four-track
multimaster films;
FIG. 3 is a diagram, partially in block form, of a portion of an
electron beam recorder and a subsystem in accordance with the
embodiment of the present invention; and
FIG. 4 is a series of timing graphs which facilitate description of
the operation of the circuitry of FIG. 3;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Before considering the operation of a system embodying the
invention, it is useful to consider the format of a film which can
be produced thereby. A coded monochrome film format for color
programming material is depicted in FIG. 1 and includes a luminance
track 20 comprised of a succession of frames 22 of black and white
pictures, and a color track 24 comprised of a succession of encoded
frames 26 each associated with a respective frame 22 and each
containing coded chroma information. It can be noted that the beam
modulated by the color signal produces rows of dots on the half of
the film it scans. The horizontal scan frequency and the color
carrier frequency are related by an integral multiple, so the dots
occur at about the same spots on each scanline. Therefore, the
color encoded frames 26 appear to be made up of thin vertical
stripes, the stripes varying in spacing in accordance with the
color information. A sync track 28 is provided on a longitudinal
strip intermediate the two successions of frames and includes a
plurality of light transmissive apertures 30 each aligned with the
upper edges of respective frames 22 and 26. One or more sound
tracks 32 along one or both edges of the film provide monaural or
binaural audio information for reproduction along with the picture
information. These audio tracks can be of magnetic form and can be
applied to the film independent of the picture information.
The film depicted in FIG. 1 would typically be one of four
individual EVR films which are slit from a printed copy of a
four-track multimaster as described above in the background
section. Portions of an electron beam recorder and associated
circuitry suitable for producing the four-track multimaster are
shown, in simplified form, in FIG. 2. The multimaster film 50 is
fed from a supply reel 51 to a takeup reel 52 by suitable film
drive means (not shown). The film 50 is enclosed in a suitable
vacuum chamber (not shown). An electron gun chamber 60 is shown as
being transparent for purposes of illustration, the enclosure 60
housing a pair of electron guns 70 and 80. The chamber 60 is
evacuated and maintained at a required vacuum level by suitable
pump means (not shown). At the end of the chamber 60 opposite the
electron gun 70 and 80 in an end plate 90 having a small aperture
or window 95 therein. Typically, the window is slightly larger than
the width of two side by side film frames and has a height which
corresponds to the height of two film frames.
The electron guns 70 and 80 simultaneously scan the film moving
past the window. Each vertical scan starts at the top of the window
and reaches the bottom of the window after one-sixtieth of a second
has elapsed. During this time the film moves a vertical distance
equivalent to the height of about one frame and the scanning beam
moves a vertical distance equivalent to about the height of two
frames. During this excursion through the window, the two electron
beams each continuously record a frame of video information and the
beams then fly back to the top of the window (during the vertical
blanking interval) to record the next pair of side-by-side
frames.
The input color video information to be recorded is received by
video processing circuitry 81 which generates luminance and encoded
chrominance signals that are suitable for modulating the intensity
of the electron gun 70 and 80 during their respective scans.
Deflection of the electron beams during recording is controlled by
horizontal and vertical deflection signals produced by a sync
signal generator 82. The vertical and horizontal sync signals are
also utilized to synchronize the video processing circuitry 81.
Sync mark processing circuitry within the video processor 82
generates an output signal that can be added to the input signal to
either electron gun 70 or 80 in order to produce the sync marks 30
which ultimately appear on the film (FIG. 1). This is accomplished,
in known manner, by unblanking one of the scanning beams during a
portion of each of the first few active scanlines of each
frame.
The entire gun chamber 60 is mounted on a slidable mechanism (not
shown) so that it can be indexed to five distinct horizontal
positions indicated in FIG. 2 by the circled designations "M" "1",
"2", "3" and "4". The "M" position is the monoscope position,
referred to above, where certain adjustments of the electron beams
can be accomplished. The four reference positions on the film
correspond to the positions on the film at which the four two-track
masters are to be recorded. Depending on the type of film used, the
images recorded on the master film with the electron beam will
generally not be visible to the eye until after a subsequent
developing step, but for purposes of illustration the frames which
have been exposed by the beam are depicted as being visible in FIG.
2. As is evident in the FIGURE, the gun chamber 60 has already
performed its function at index position "1" so that the first
two-track master has been completely recorded on the film. The gun
chamber was then moved to index position "2" where it is now shown
during the operation of exposing the second two-track master on a
multimaster film 50. When this is complete the multimaster 50 will
be rewound and the gun chamber 60 moved to index position "3" and,
after appropriate recording, to index position "4".
Located just above the window 95 and over the positions of the two
side-by-side frame tracks being recorded are a pair of "VIT" plates
96 and 97. The raster scans of the beams from electron gun 70 and
80 are preadjusted to impinge upon these plates during the initial
horizontal line scans which occur during a portion of the vertical
blanking interval between fields of video information. The video
processing circuitry 81 inserts appropriate test signals in the
vertical blanking interval which may, for example, modulate the
electron beams with a prescribed grey scale stairstep signal. The
plates are formed of a material such as molybdenum which acts as an
anode, so the signals from output conductors 96A and 97A, coupled
to the plates, indicate the instantaneous intensities of the
electron beams at various amplitude levels. These outputs are
received by automatic gain control circuits 98 and 99 which
regulate the gain level of the electron guns 70 and 80 by applying
appropriate control signals over lines 98A and 99A.
Up to this point, the detailed description of the beam recording
apparatus has dealt with a system that is presently known in the
art. Referring to FIG. 3, there is shown an embodiment of a system
in accordance with the improvement of the present invention. An
enlargement of the window 95 is shown in conjunction with the VIT
plates 96 and 97. Only one electron gun 70 and the beam therefrom
are shown in FIG. 3 along with circuitry for controlling same, but
it will be appreciated that similar circuitry is used to control
the other electron gun.
In the present embodiment of the invention the VIT plates 96 and 97
are provided with vertical slots 101 and 102, respectively. These
thin slots may be cut into the VIT plates and can have a typical
width of about 0.005 inch. The important property of each of the
slots is that it gives rise to a discontinuity in the output taken
from the VIT plate when an electron beam is scanned over the slot.
Thus, the slot acts as a precisely located "interrupt means" and it
will be appreciated that alternate means for accomplishing such an
interruption, for example a masking of a portion of the plate,
could be employed. The output of the plate 96 is coupled over the
output conductor 96A to AGC circuitry, as was shown in FIG. 2, and
is also coupled to an input of a gate 110. The gate 110 is enabled
by a circuit which consists of a pair of monostable or "one-shot"
multivibrators 120 and 130, a line counter 140, and an AND gate
150. The one-shot multivibrator 120 receives as an input the
horizontal sync pulse and generates a positive-going output pulse
for the duration of its intrinsic unstable state. This "on" time is
typically selected as being about 20 microseconds. The output of
one-shot 120 is coupled to the other one-shot multivibrator 130
which is adapted for triggering by the negative-going voltage
excursion which occurs when one-shot 120 goes "off;" i.e., it is
triggered 20 microseconds after the horizontal sync pulse, H. The
one-shot 130 is provided with a short intrinsic unstable state time
of about 5 microseconds, so it generates a positive-going pulse on
output line 130A, the pulse occurring from about 20 microseconds
after the start of a scanline and continuing until about 25
microseconds after the start of the scanline. The line 130A is one
of two inputs to AND gate 150, the other input being the output of
a line counter 140. The line counter 140 receives the vertical and
horizontal input pulses from the sync signal generator 82 (FIG. 2)
and produces an output only during the first three lines of each
scanning field. The output of AND gate 150, which enables the gate
110, is thus present for 5 microseconds at about the center of each
of the first three horizontal scanlines of each scanning field.
During the presence of the enable signal from AND gate 150, the
signal on conductor 96A is passed by the gate 110 to the sampling
input of a smaple and hold circuit 160. The other input to the
circuit 160 is the output of a ramp generator 170 which is, in
turn, triggered by the horizontal sync pulse H. The output of
sample and hold circuit 160 is a correction signal which is applied
to the horizontal centering circuitry of the electron gun 70.
A description of the operation of the circuitry of FIG. 3 is
facilitated by referring to the graphs of FIG. 4. The graph 4A
shows the output derived from VIT plate 96 during two successive
scanlines which occur during the vertical interval when the
electron beam is scanned the VIT plate and crossing the slot 101.
The "video" information during these scanlines consists of a
stairstep test pattern of the type shown. The negative-going pulses
P result from the beam crossing the slot 101 and the accordant
interruption of the VIT plate output. The graph 4B shows the timing
of the horizontal sync pulses, the time base of all graphs in FIG.
4 being the same. Graph 4C illustrates the output of the one-shot
multivibrator 120. The one-shot 120 is triggered by the leading
edge of the horizontal sync pulse, and the output of the one-shot
is "on" for 20 microseconds whereupon it returns to the "off"
state. FIG. 4D shows the output of the one-shot 130 which is
triggered by the trailing edge of the output of one-shot 120 and
then remains "on" for 5 microseconds.
The slot 101 is positioned at a prescribed horizontal reference
which lies, for example, at the center of the VIT plate 96. For a
properly positioned raster scan (assuming good scan linearity) the
electron beam should pass the slot 101 at a predetermined time
after the occurrence of the horizontal sync pulse H. In the present
embodiment the nominal predetermined time is 22.5 microseconds
after the leading edge of H. The circuit of FIG. 3 in effect
compares the relative timing of the occurrence of the interrupt
pulse P to the relative timing of the scanline during the vertical
interval. An appropriate correction signal is then generated in
accordance with the comparison and utilized to correct the position
of the raster with respect to the window 95.
Returning to FIG. 4, the graph 4E shows the output of gate 110
(inverted) as being coincident in time with the pulses of graph 4A.
The purpose of generating the gating signal on line 130A is to
extract the pulse P from the vertical interval test signal and
prevent the occurrence of extraneous pulses except at the
approximate center of the scanlines where this "interrupt" pulse is
expected. The output of the gate 110, i.e., the pulses of graph 4E,
are utilized to sample the sawtooth voltage shown in graph 4F and
produced by the ramp generator 170. The ramp is triggered by the
leading edge of the horizontal sync pulse H and has a prescribed
rise time. Therefore, the ramp contains intrinsic information
concerning the timing of horizontal scanlines. The voltage to which
the sawtooth rises after 22.5 microseconds is selected as a nominal
correction voltage V.sub.o. Thus, if the raster is properly
positioned with respect to the window 95 the sampled voltage will
be V.sub.o, a voltage which will not change the centering of gun
70. Similarly, if the raster is initially positioned slightly
toward the left or right with respect to the proper horizontal
reference position, the pulse P will respectively occur slightly
before or after 22.5 microsecond reference. This will result in the
sampled voltage being respectively lower (V.sub.- in FIG. 4) or
higher (V.sub.+ in FIG. 4) than the nominal correction voltage by
an amount proportional to the magnitude of the shift. These
correction voltages result in an appropriate shift in the centering
of electron gun 70 which tends to return the correction voltage to
the nominal value, V.sub.o. The holding capacitor in circuit 160 is
charged through a relatively low resistance so that it has a
relatively fast charge time and is discharged through a relatively
high resistance so that it has a relatively slow discharge time, of
the order of many video fields. In this manner, the error signal
accumulated during the appropriate lines of the interval is applied
during the active field portions without substantial
degradation.
The invention has been described with reference to a particular
embodiment but it will be appreciated that variations within the
spirit and scope of the invention will occur to those skilled in
the art. For example, the means for comparing the timing of the
interrupt signal to the scanline timing could take various
alternate forms. Also, the slots 101 and 102 could have alternate
shapes, such as a wedge shape. If desired, a correction of vertical
scan position could also be achieved using the principles of the
invention.
* * * * *