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Claims  |
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What is claimed as new and desired to be protected by Letters Patent is set
forth in the appended claims.
1. In a method of scanning originals bearing pictorial images, and the
like, and reproducing such images, in combination, the steps of
illuminating an original with first and second light and projecting the
image of the original onto a copy carrier; detecting the spatial variation
of the intensity of the first light after the first light has been
modulated in intensity by the image on the original; and changing the
contrast of the image projected onto the copy carrier compared to the
contrast of the image on the original by changing the spatial variation of
the intensity of the second light in dependence upon the detected spatial
variation of the intensity of the modulated first light, wherein said
illuminating step comprises illuminating the original with a first and
with a second light source, respectively producing said first and second
light, wherein said detecting step comprises deflecting light which has
been modulated by the image on the original and which is being projected
towards the copy carrier away from the copy carrier and projecting such
deflected light onto a light detector through a filter which blocks the
second light furnished and using the light detector to generate a
light-intensity-indicating electrical signal, and wherein said step of
changing the contrast comprises applying the electrical signal to the
light-intensity control input of the second light source to control the
intensity of the illumination of the image on the original effected by the
second light source in dependence upon the detected modulated intensity of
the deflected first light.
2. In a method as defined in claim 1, said first light source comprising a
first cathode ray tube, said second light source comprising a second
cathode ray tube and intermediate the image screen of the latter and the
original a filter which passes substantially only light which is blocked
by the filter associated with the light detector, and wherein said step of
illuminating comprises causing the electron beam of each cathode ray tube
to scan a raster and form a flying spot on the image screen of the
respective cathode ray tube and deriving from the two flying spots
coincident flying light beams, and illuminating the original with the
coincident flying light beams.
3. In a method as defined in claim 1, said first light source producing
light which illuminates all portions of the image on the original
simultaneously, and said second light source comprising a cathode ray tube
and intermediate the image screen of the tube and the original a filter
which passes substantially only light which is blocked by the filter
associated with the light detector, said light detector comprising a
vidicon located back of the associated filter, wherein said step of
illuminating comprises causing the electron beam of the cathode ray tube
to scan a raster and form a flying spot on the image screen of the cathode
ray tube and deriving from the flying spot a flying light beam and
illuminating the original with the flying light beam, wherein said step of
detecting the intensity of the first light comprises scanning the charge
density image on the photoconductive surface of the vidicon in synchronism
with scanning effected by the electron beam of the cathode ray tube, and
wherein said step of changing the contrast comprises applying the video
output signal of the vidicon to the spot-brightness control input of the
cathode ray tube.
4. In a method of scanning originals being pictorial images, and the like,
and reproducing such images, in combination, the steps of illuminating an
original with first and second light and projecting the image of the
original onto a copy carrier; detecting the spatial variation of the
intensity of the first light after the first light has been modulated in
intensity by the image on the original; and changing the contrast of the
image projected onto the copy carrier compared to the contrast of the
image on the original by changing the spatial variation of the intensity
of the second light in dependence upon the detected spatial variation of
the intensity of the modulated first light, wherein said step of
illuminating an original comprises effecting a line-by-line scanning of
the original with a flying light-beam derived from a flying light spot
traced on the image screen of a cathode ray tube, with said first and
second light being the light of said flying light beam during the tracing
by the latter of alternate respective first and second scan lines, wherein
said step of illuminating an original further includes maintaining the
intensity of the flying light beam substantially constant during the
tracing of each first scan lines, and wherein said step of detecting
comprises registering during the tracing of each first scan line the
variation with respect to time of the intensity of the light beam as
modulated by the image on the original, and wherein said step of changing
the contrast comprises applying to the spot-brightness control input of
the cathode ray tube during the tracing of each second scan line a control
signal which varies in time in correspondence to the light beam intensity
variation registered during the tracing of the preceding scan line.
5. In a method as defined in claim 4, wherein said step of detecting
comprises using a photoelectric detector operative for generating an
electrical signal having an instantaneous value indicative of the
instantaneous intensity of the light incident upon the photoelectric
detector, and wherein said step of changing the contrast further comprises
applying the electrical signal generated by the photoelectric detector to
the input of a time-delay device having a time delay equal to the time
interval required for the tracing of one scan line and applying the output
signal of the time-delay device to the spot-brightness control input of
the cathode ray tube during the tracing of each second scan line.
6. In a method as defined in claim 5, said copy bearer comprising
light-sensitive material, wherein said step of maintaining the intensity
of the flying light beam substantially contrast during the tracing of the
first scan lines comprises maintaining such intensity constant at a value
such that the portions of the image on the original scanned during the
tracing of the first scan lines are projected onto the copy bearer as
light images of such low intensity as to have a first effect upon the
light-sensitive material of the copy bearer, and wherein said step of
detecting further comprises amplifying the electrical signal generated by
the photoelectric detector to such an extent that the portions of the
image on the original scanned during the tracing of the second scan lines
are projected onto the copy bearer as light images of an intensity
sufficient to have a second effect upon the light-sensitive material of
the copy bearer, and wherein said value and the amplification of the
electrical signal are such that said first effect is negligible compared
to said second effect.
7. In a method as defined in claim 5, the spot-brightness control input of
the cathode ray tube being connected by an electronic switchover device to
the output of the time-delay stage and to the output of a D.C. voltage
source, wherein said step of illuminating an original, said step of
detecting the intensity of the first light, and said step of changing the
contrast together comprise activating the electronic switchover device
with an activation frequency equal to the line frequency of the scanning
raster of the cathode ray tube.
8. An apparatus for scanning originals bearing pictorial images, and the
like, and reproducing such images, comprising, in combination,
illuminating means operative for illuminating an original with first and
second light and projecting the image of the original onto a copy carrier;
detecting means operative for detecting the spatial variation of the
intensity of the first light after the first light has been modulated in
intensity by the image on the original; and contrast-changing means
operative for changing the contrast of the image projected onto the copy
carrier compared to the contrast of the image on the original by changing
the spatial distribution of the intensity of the second light in
dependence upon the detected spatial variation of the intensity of the
modulated first light, wherein said illuminating means comprises first and
second light sources producing said first and second light, said second
light source having a light-intensity control input, wherein said
detecting means comprises a photoelectric detector, deflecting means
operative for deflecting light which has been modulated in intensity by
the image on the original and which is being projected towards the copy
carrier away from the copy carrier and projecting such deflected light
towards said photoelectric detector, and intermediate said deflecting
means and said photoelectric detector a filter which blocks the second
light, and wherein said contrast-changing means comprises means for
applying to the light-intensity control input of said second light source
a control signal derived from the output signal of said photoelectric
detector.
9. An apparatus as defined in claim 8, wherein said first light source
comprises a first cathode ray tube, and wherein said second light source
comprises a second cathode ray tube and intermediate the image screen of
the latter and the original a filter which passes substantially only light
which is blocked by said filter of said detecting means, wherein said
illuminating means further comprises synchronizing means for synchronizing
the tracing of rasters by the flying spots on the image screens of the two
cathode ray tubes and optical means operative for deriving from the two
flying spots coincident flying light beams and illuminating the original
with the coincident flying light beams.
10. An apparatus as defined in claim 8, wherein said first light source
comprises means for illuminating with first light all portions of the
image on the original simultaneously, wherein said second light source
comprises a cathode ray tube and intermediate the image screen of the
latter and the original a filter which passes substantially only light
which is blocked by the filter of the detecting means, wherein said
illuminating means further comprises scanning control means operative for
causing the electron beam of the cathode ray tube to form on the image
screen thereof a flying spot which traces a raster and optical means
operative for deriving from the flying spot a flying light beam and
illuminating the image on the original with the flying light beam, wherein
said photoelectric detector comprises a vidicon located behind the filter
of the detecting means, wherein said detecting means further comprises
means for scanning the charge density image on the photoconductive surface
of the vidicon in synchronism with the scanning effected by the flying
light beam, and wherein said contrast-changing means comprises means for
applying to the spot-brightness control input of the cathode ray tube a
contrast-control signal derived from the video output signal of the
vidicon.
11. An apparatus as defined in claim 9, wherein in said deflecting means
comprises first semitransmissive mirror means located in the path of the
light modulated by the image on the original and arranged to transmit part
of the modulated light towards the copy carrier and to deflect the
remainder of the modulated light towards the photoelectric detector, and
wherein said optical means of said illuminating means comprises means for
deriving from the flying spot of the second cathode ray tube a second
light beam and second semitransmissive mirror means arranged to deflect
such second light beam along a path coincident with the light beam derived
from the flying spot of the first cathode ray tube, and wherein said means
for applying to the light-intensity control input of the second light
source a control signal derived from the output signal of the
photoelectric detector includes an amplifier connected between the output
of the photoelectric detector or and the spot-brightness control input of
the second cathode ray tube.
12. An apparatus as defined in claim 10, wherein said deflecting means
comprises first semitransmissive mirror means located in the path of the
light modulated by the image on the original and arranged to transmit part
of the modulated light towards the copy bearer and to deflect the
remainder of the modulated light towards the photoconductive surface of
the vidicon, wherein said first light source comprises means for
illuminating with first light all portions of the image on the original
simultaneously and uniformly, and wherein said first light source, the
image on the original and the copy bearer define a main optical light
path, and wherein said cathode ray tube is located outside said main
optical light path, and wherein said optical means comprises second
semitransmissive mirror means arranged in said main path to bend the
flying light beam derived from the flying spot of the cathode ray tube
into said main optical path while transmitting to the original the light
from said first light source.
13. An apparatus as defined in claim 9, wherein the filter of said second
light source and the filter of said detecting means are polarization
filters having polarization axes crossed relative to each other.
14. An apparatus as defined in claim 10, wherein the filter of said second
light source and the filter of said detecting means are polarization
filters having polarization axes crossed relative to each other.
15. An apparatus as defined in claim 9, wherein the filter of said second
light source and the filter of said detecting means are color filers of
complementary colors.
16. An apparatus as defined in claim 10, wherein the filter of said second
light source and the filter of said detecting means are color filters of
complementary colors.
17. An apparatus for scanning originals bearing pictorial images, and the
like, and reproducing such images, comprising, in combination,
illuminating means operative for illuminating an original with first and
second light and projecting the image of the original onto a copy carrier;
detecting means operative for detecting the spatial variation of the
intensity of the first light after the first light has been modulated in
intensity by the image on the original; and contrast-changing means
operative for changing the contrast of the image projected onto the copy
carrier compared to the contrast of the image on the original by changing
the spatial distribution of the intensity of the second light in
dependence upon the detected spatial variation of the intensity of the
modulated first light, wherein said illuminating means comprises a cathode
ray tube, scanning control means operative for causing the electron beam
of the cathode ray tube to form on the image screen thereof a flying spot
which traces a raster a first time and then a second time, and optical
means for deriving from the flying spot a flying light beam and
illuminating the image on the original with the flying light beam, the
light of the beam constituting the first light and constituting the second
light during the first and second tracings, respectively, wherein said
detecting means comprises light registering means operative during the
first tracing for registering the variation with respect to time of the
intensity of the modulated light beam, and wherein said contrast-changing
means comprises means operative during the second tracing for reading out
the light registering means in synchronism with the second tracing and
applying to the spot-brightness control input of the cathode ray tube a
control signal derived from the output signal of the light registering
means.
18. An apparatus as defined in claim 17, wherein said detecting means
comprises means for deflecting a portion of the light of the flying light
beam at a location where such light has been modulated in intensity by the
image on the original, and wherein said light registering means is
positioned in the path of the deflected light.
19. An apparatus for scanning originals bearing pictorial images, and the
like, and reproducing such images, comprising, in combination,
illuminating means operative for illuminating an original with first and
second light and projecting the image of the original onto a copy carrier;
detecting means operative for detecting the spatial variation of the
intensity of the first light after the first light has been modulated in
intensity by the image on the original; and contrast-changing means
operative for changing the contrast of the image projected onto the copy
carrier compared to the contrast of the image on the original by changing
the spatial distribution of the intensity of the second light in
dependence upon the detected spatial variation of the intensity of the
modulated first light, wherein said illuminating means comprises a cathode
ray tube, scanning control means operative for causing the electron beam
of the cathode ray to form on the image screen thereof a flying spot which
traces a raster comprised of first scan lines alternating with second scan
lines, and optical means operative for deriving from the flying spot a
flying light beam and illuminating the image on the original with the
flying light beam, and wherein said detecting means comprises registering
means operative during the tracing of each first scan line for registering
the variation with respect to time of the intensity of the light beam as
modulated by the image on the original, and wherein said contrast-changing
means comprises brightness control means operative for applying to the
spot-brightness control input of the cathode ray tube during the tracing
of each first scan line a control signal which maintains the intensity of
the flying light beam constant and during the tracing of each second scan
line a control signal which varies in time in correspondence to the light
beam intensity variation registered during the preceding tracing of a
first scan line.
20. An apparatus as defined in claim 19, wherein said registering means
comprises a photoelectric detector operative for generating an electrical
signal having an instantaneous value indicative of the instantaneous
intensity of the light incident upon the photoelectric detector and a
time-delay device having an input connected to the output of the
photoelectric detector and exhibiting a time delay equal to the time
required for the tracing of one scan line, and wherein said brightness
control means of said contrast-changing means comprises means operative
during the tracing of each second scan line for applying to the
spot-brightness control input of the cathode ray tube the output signal of
said time delay device.
21. An apparatus as defined in claim 19, wherein said registering means
comprises a photoelectric detector operative for generating an electrical
signal having an instantaneous value indicative of the instantaneous
intensity of the light incident upon the photoelectric detector and a
time-delay device having an input connected to the output of the
photoelectric detector and exhibiting a time delay equal to the time
required for the tracing of one scan line, and wherein said brightness
control means of said contrast-changing means comprises a D.C. voltage
source and electronic switch means connecting the spot-brightness control
input of the cathode ray tube to the output of the D.C. voltage source and
to the output of the time-delay device and operative for applying to the
spot-brightness control input the output voltage of the D.C. voltage
source during the tracing of each first scan line and operative for
applying to the spot-brightness control input the output signal of the
time delay device during the tracing of each second scan line.
22. In a method of scanning originals bearing optical images, and the like,
and reproducing such images, in combination, the steps of illuminating an
original with first and second light and projecting the image of the
original onto a copy carrier; detecting the spatial variation of the
intensity of the first light after the first light has been modulated in
intensity by the image on the original; and changing the contrast of the
image projected onto the copy carrier compared to the contrast of the
image on the original by changing the spatial variation of the intensity
of the second light in dependence upon the detected spatial variation of
the intensity of the modulated first light, wherein said step of
illuminating an original comprises scanning the original with a flying
light beam of substantially constant intensity derived from a flying light
spot on the image screen of a cathode ray tube, the light of said flying
light beam constituting said first light, wherein said step of detecting
the intensity of the first light comprises deflecting a portion of the
light of the flying light beam at a location where such light has been
modulated in intensity by the image on the original and projecting such
deflected light onto the light-sensitive surface of a storage device
capable of registering the intensity value of such deflected light during
the course of at least one complete scanning of the image on the original,
and wherein said step of changing the contrast comprises thereafter again
scanning the original with the flying light beam and during such scanning
reading out the storage device in synchronism with such scanning and
applying the output signal of the storage device to the spot-brightness
control input of the cathode ray tube. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates to the scanning and reproduction of originals bearing
pictorial images, and the like.
In many photographic copying processes -- for example, the production of
color-paper images, the duplication of diapositives, the production of
color negatives from color positives or the making of black-and-white
take-offs from color films -- it is necessary or desired to change the
gradation of the reproduced image, compared to the gradation of the image
on the original. In general what is involved, in effect, is a reduction of
the value of the exponent gamma of the characteristic curve. Dark regions
should be brightened, and light regions darkened; however, other gradation
changes may also be desired in some circumstances.
It is known to use as the light source in such a copying operation a
cathode ray tube the spot brightness of which is controlled. The flying
spot formed on the image screen of the tube traces a raster, which is
projected onto a transparent original. The major portion of the
transmitted light is projected by means of image-forming optics onto the
light-sensitive material, causing an image-forming chemical reaction. The
remainder of the transmitted light is directed onto a photodetector which
generates a signal for controlling the intensity of the illuminating
flying light beam derived from the flying spot of the cathode ray tube. In
this way, the spatial distribution of the density of the transparent image
has a controlling effect upon the illuminating light source; this feedback
action results in a change of the contrast of the reproduced image
compared to the contrast of the image on the original.
With the known system, in consequence of the aforedescribed feedback, there
are formed in the reproduced image a plurality of dark and bright stripes
or striations oriented parallel to an edge which runs perpendicular to the
scanning direction. The width of these stripes depends upon the
propagation-time-dependent phase shift introduced in the electro-optical
feedback branch of the system.
SUMMARY OF THE INVENTION
It is the general object of the invention to provide a method, and
apparatus for performing the method, such that the undesirable stripes or
striations referred to above are not produced.
This object, and others which will become more understandable from the
description, below, of specific embodiments, can be met, according to one
advantageous concept of the invention, by providing a control circuit for
the illumination of the image on the original and a compensation circuit
for modifying the spatial variation of the illuminating light in
dependence upon the spatial variation of the light modulated by the image
on the original. According to the inventive concept, the compensation
circuit is de-coupled from the control circuit. The gradation modification
is advantageously so performed that in the control circuit, by means of a
semitransmissive mirror, a part of the modulated light is coupled out,
thereafter filtered by a filter, and then applied to a photodetector. The
intensity-indicating signal generated by the photodetector is applied to a
compensation circuit comprised of an amplifier and a second light source
and is amplified in a manner which modifies the contrast of the reproduced
image. The light emitted by the just mentioned second light source is
filtered by means of a second filter, complementary to the first filter
mentioned above, and is bent by means of a semitransmissive mirror into
the main light path of the light which illuminates the image on the
original and becomes projected onto the copy carrier.
With the above approach, it is preferred to use as the light source two
synchronously controlled cathode ray tubes arranged congruently relative
to the image on the original, or else to use a first light source which
uniformly and simultaneously illuminates all portions of the image on the
original in conjunction with a vidicon and a cathode ray tube for
effecting the desired modification of the contrast.
According to a further advantageous concept of the invention, there is
performed a uniform first illumination of the image on the original by
means of a cathode ray tube. Thereafter, a part of the light modulated by
the image on the original is coupled out of the control circuit and the
signal for the entire image on the original is stored. During a second
illumination of the image, the stored signal is read out, amplified for
the purpose of modifying the contrast of the reproduced image, and
visually displayed on the screen of the cathode ray tube. The light image
on the cathode ray tube is used as illuminating light having a spatial
intensity variation, and this illuminating light supplements the effect of
the illuminating light employed during the aforementioned first
illumination.
Instead of storing the entire image, it is also possible to perform the
detection of the extent to which the first light is modulated by the image
on the original, and the compensating illumination using second light,
during the tracing of alternate scan lines of the cathode-ray-tube light
source. With this approach, the intensity-indicating signal furnished by
the photodetector is caused to be delayed by a time interval equal to the
time interval required for the tracing of one scan line.
In the latter case, it is advantageous if the first light is of such
intensity that the light reaching the copy carrier during the tracing of
the first scan lines has no effect or only a negligible effect upon the
copy carrier, e.g., photographic paper, with the intensity-indicating
signal of the light detector being delayed by the time interval required
for the tracting of one scan line and being used during the tracing of the
next scan line for controlling the intensity of the illuminating beam
derived from the flying spot on the image screen of the cathode ray tube.
With this approach, it is advantageous to connect the spot-brightness
control input of the cathode ray tube alternately to the output of a
suitable time-delay stage and to the output of a source of constant
voltage, for example by means of an electronic switchover stage activated
at the scanning line frequency.
The novel features which are considered as characteristic for the invention
are set forth in particular in the appended claims. The invention itself,
however, both as to its construction and its method of operation, together
with additional objects and advantages thereof, will be best understood
from the following description of specific embodiments when read in
connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1-4 depict four different inventive systems which can be employed to
perform four different versions of the inventive method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 depicts schematically a first embodiment of the inventive contrast
control arrangement. For the sake of clarity, the optical systems present
to form the requisite images are shown only very schematically in the
drawing. A first cathode ray tube KR1 is employed as a point-light-source
scanning tube. It displays upon its image screen, in per se known manner,
a scanning raster of uniform light intensity. By means of schematically,
illustrated optics, this scanning raster is projected onto the original V
to be copied. The original V can for example be a transparent diapositive
or a negative. An image of the original V itself is in turn projected, by
means of further schematically illustrated optics, onto the copy bearer K,
which can for example be ordianry photographic paper. A beam splitter S1
is arranged in the main path of the light intermediate cathode-ray-tube
light source KR1 and copy bearer K. Part of the light travelling along
this main light path from the light source KR1 to the beam splitter S1 is
deflected out of the main light path and directed onto the cathode of a
photoelectric detector P. Intermediate the photo-electric detector P and
the beam splitter S1 there is arranged a filter F1. This filter can, for
example, be a color filter or a polarization filter.
The electrical signal generated by the photoelectric detector P corresponds
to the modulation by the original V of the light originating from light
source KR1 and passing through the original V. This electrical signal is
applied to a variable-gain amplifier Vs, and then in amplilfied form is
applied to the conventional electron-beam-intensity control electrode of a
second cathode ray tube KR2. The gain furnished by the amplifier Vs
influences the contrast in the image ultimately formed on copy bearer K.
The front of the image screen of the cathode ray tube KR2 there is arranged
a second filter F2 which is complementary to the first filter F1. If the
filters are polarization filters, the polarization axes of the filters F1,
F2 are crossed relative to each other; if the filters are color filters,
the filters are of complementary colors.
The image appearing on the screen of the second cathode ray tube KR2, by
means of schematically illustrating optics, is projected towards a second
beam splitter S2, which deflects the image back into the main light path
extending from the light source KR1 to copy bearer K. More accurately, at
any given moment, the point of light appearing on the screen of tube KR2,
by means of nonillustrated optics, is projected, in the form of a light
beam, towards the second beam splitter, which deflects the beam back into
the main light path. The x and y deflection control circuitry for the two
cathode ray tubes KR1, KR2 is synchronized. This is schematically
indicated in FIG. 1 by the presence of the so-called scanning
synchronizer. It will be understood that the x and y deflection signals
applied to the x and y deflection coils of one cathode ray tube are
simultaneously applied to the deflection coils of the other cathode ray
tube. In this way, the flying spots formed on the image screens of the two
tubes trace respective rasters in synchronism with each other. Likewise,
the illustrated optics derives from the two synchronized flying light
spots corresponding flying light beams which are projected towards the
original V exactly coincident with each other.
Because the two filters F1, F2 are complementary to each other, the light
originating from the screen of light source KR2 and passing through
original V cannot reach the photoelectric detector P. Accordingly, this
has no effect upon the compensation or feedback circuit P, Vs, KR2. As a
result, a feedback action involving this light component and the
associated formation of a striated image do not occur.
FIG. 2 depicts a second embodiment of an arrangement for performing the
inventive method. In the embodiment of FIG. 2, a conventional light source
L and a vidicon Vi respectively replace the cathode-ray-tube
point-light-source KR1 and photoelectric detector P of the embodiment
shown in FIG. 1. In the embodiment of FIG. 2, as in that of FIG. 1, a
contrast-controlling light image is produced on the screen of the cathode
ray tube KR2, and this contrast-controlling light is deflected by beam
splitter S2 and transmitted through the original V to the copy bearer K.
The videa signal output of the vidicon Vi is depicted connected to the
input of amplifier Vs. The x and y deflection coils of the cathode ray
tube KR2 and of the electron beam scanning device in the vidicon are
operated in synchronism with each other, schematically as indicated in
FIG. 2 by the presence of the scanning synchronizer. Accordingly, the
charge-density image formed on the photoconductive surface of the vidicon
is scanned in synchronism with the tracing of a raster by the flying spot
on the image screen of cathode ray tube KR2.
FIG. 3 depicts a third inventive arrangement for performing the inventive
method. A constant D.C. voltage is applied to the electron-beam-intensity
control input of the cathode ray tube KR, resulting in the production of
an unmodulated, uniform-intensity scanning raster on the screen of the
tube. This unmodulated light raster is projected, by means of
schematically illustrated optics, through the transparent original V, and
becomes modulated as a result. The thusly modulated light beam is in part
deflected by beam splitter S out of the main light path and directed onto
the photoelectric surface of a photoelectric detecotr P. The latter
generates a corresponding electrical signal which is then amplified by
amplifier Vs and transmitted to storage device Sp. The storage device Sp
stores the values of the videa signal for the entire image of the original
V.
Thereafter, the spot-brightness control input of the cathode ray tube is
connected to the output of an amplifier Vs', the input of which is
connected to the output of the storage device Sp. As a result, the
modulated light raster now appears on the image screen of the cathode ray
tube KR, and the light of this contrast-controlling modulated light raster
is projected through the original V onto the copy bearer K. The amplifier
Vs and/or the amplifier Vs' is a variable-gain amplifier, to permit
variation of the contrast of the image formed on the copy bearer K.
The exposure of the copy bearer K to light can be performed in two steps.
In the first step, light from the unmodulated, uniform-intensity light
raster on the screen of tube KR is projected through the original V and
registered by the storage device Sp. Some of the light passing through the
original V will also fall upon the copy bearer K, producing an image
having unmodified contrast. In the second step, the modulated light raster
on the screen of tube KR is projected through the original V and onto the
copy bearer K, producing an image having modified contrast. During this
second step, the beam splitter S can be removed, if desired.
To switch over from the first to the second step use is made of a set of
switches K1, K2. During the first step, the switch K1 applies the constant
D.C. voltage furnished by a D.C. voltage source G to the
electron-beam-intensity control electrode of the cathode ray tube KR, the
switch K2 connects the output of the photoelectric detector P to the input
of the storage device Sp. During the second step, the switch K1 connects
the output of storage device Sp to the electron-beam-intensity control
electrode of the cathode ray tube KR, through the intermediary of the
amplifier Vs', whereas the switch K2 disconnects the output of amplifier
Vs from the input of storage device Sp.
The first step can be performed in such a manner that the light projected
from the unmodulated light raster on the screen of tube KR and passing
through the original V has so low an intensity as to be detected by the
photoelectric detector P, while not having any appreciable effect upon the
copy bearer K, for example photographic paper.
The storage device Sp can for example be a plate storage device, a drum
storage device or a storage tube. Whatever the form of the storage device
Sp, it is to be understood that the orderly write-in of information and
the orderly read-out of information are synchronized with the tracing of a
light raster by the flying spot on the image screen of the cathode ray
tube KR. This is schematically indicated in FIG. 3 by the presence of a
synchronizer. For example, if the storage device Sp is a storage tube the
x and y deflection control signals applied to the deflection control
circuitry of the cathode ray tube KR can also be applied to the deflection
unit of the storage tube for use as synchronizing signals, both during the
recording of a video signal and during playback of the recorded video
signal.
FIG. 4 schematically depicts a fourth inventive arrangement for performing
the inventive method. The main light path is the same as in FIG. 3.
However, instead of the storage device Sp, use is made of a time delay
stage V2, exhibiting a time delay equal to the time required for the
scanning of one line during the cathode-ray-tube scanning operation. The
time-delay stage Vz can for example be a delay line, a delay-line network,
a bucket-brigade-type storage device (see for example "Electronics", Feb.
28, 1972, Laurence Altman: "Bucket brigade devices . . . "), or the like.
An electronic switch ES, operating with the line frequency of the scanning
cycle, and switched simultaneously with the deflecting arrangement of the
cathode ray tube, alternately connects the time-delay stage Vz and a D.C.
voltage source G with the electron-beam-intensity control electrode of the
cathode ray tube. The electronic switching device ES can for example
comprise two gates, each having a first input and a second input, and a
flip-flop having a toggle or complementing input and two outputs. The
first input of the first gage would be connected to the output of D.C.
voltage source G, and that of the second gate to the output of delay stage
Vz. The second input of the first gate would be connected to the first
output of the flip-flop, while that of the second gate would be connected
to the second output of the flip-flop. The toggle or complementing input
of the flip-flop would be connected to the illustrated line-frequency
control circuit ZF. The outputs of the two gates would be connected to the
two inputs of an OR-gate, the output of which would constitute the output
of stage ES. The line-frequency control circuit ZF, very conventiently,
can be part of the control signal generator which controls the deflection
of the electron beam of the cathode ray tube KR. For example, if
horizontal synch pulses are applied to the deflection control circuit of
the cathode ray tube control circuitry, such synch pulses can be
simultaneously applied to the control input of switching circuit ES, to
active the latter at the scanning line frequency.
In this embodiment too, the applied D.C. voltage can be selected so low
that the light from the light raster on the tube screen, after passing
through the original V, is of sufficient intensity to be properly detected
by the photoelectric detector P, while being of too low an intensity to
have an appreciable effect upon the copy bearer K, for example
photographic paper.
The inventive method and the inventive apparatuses for its performance are
also suitable for additive color copying processes, with the steps for
each of the three primary colors being performed successively. In this
event, in the embodiments shown in FIGS. 1 and 2, the use of complementary
polarization filters is preferred over the use of complementary color
filters.
It will be understood that each of the elements described above, or two or
more together, may also find a useful application in other types of
circuits and constructions differing from the types described above. While
the invention has been illustrated and described as embodied in a printer
which prints onto photographic paper, it is not intended to be limited to
the details shown, since various modifications and structural changes may
be made without departing in any way from the spirit of the present
invention.
Without further analysis, the foregoing will so fully reveal the gist of
the present invention that others can, by applying current knowledge,
readily adapt it for various applications without omitting features that,
from the standpoint of prior art, fairly constitute essential
characteristics of the generic or specific aspects of this invention.
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