U.S. patent number 3,680,956 [Application Number 05/099,106] was granted by the patent office on 1972-08-01 for apparatus for controlling contrast during reproduction of photographic images.
Invention is credited to Peter Custer.
United States Patent |
3,680,956 |
Custer |
August 1, 1972 |
APPARATUS FOR CONTROLLING CONTRAST DURING REPRODUCTION OF
PHOTOGRAPHIC IMAGES
Abstract
A method and apparatus for controlling contrast during the
reproduction of photographic images from a negative or
transparency. A mask is formed in a sheet of phototropic material
by placing the sheet in the focal path of the image and
transmitting the image to the sheet by a sheet-activating radiation
source. Phototropic materials characteristically darken on exposure
to a radiation source of certain wavelengths. The intensity of the
radiation source may be selectively varied to produce a masking
image of the desired density. The reproduction exposure is then
made through the original image and the mask formed on the
phototropic sheet prior to clearing of the masking image.
Inventors: |
Custer; Peter (Newtown,
PA) |
Family
ID: |
22272764 |
Appl.
No.: |
05/099,106 |
Filed: |
December 17, 1970 |
Current U.S.
Class: |
355/71;
355/80 |
Current CPC
Class: |
G03B
27/72 (20130101); G03B 27/727 (20130101) |
Current International
Class: |
G03B
27/72 (20060101); G03b 027/76 () |
Field of
Search: |
;355/35,71,77,80,132,133
;350/160 ;250/237 |
Foreign Patent Documents
|
|
|
|
|
|
|
891,992 |
|
Mar 1962 |
|
GB |
|
873,380 |
|
Jul 1961 |
|
GB |
|
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Adams, Jr.; Russell E.
Claims
I claim:
1. Apparatus for masking motion picture film and the like
comprising means for advancing the film successively through first,
second and third stations, the first station comprising density
sensing means for sensing the image contrast range of each frame of
the film, the second station comprising a mask forming station,
said mask forming station comprising means for projecting the
images of said film onto a phototropic material contiguous said
film to activate said phototropic material to form masking images
thereon, said latter means being controlled by said density sensing
means to provide masking images commensurate with the film image
density, the third station comprising a printing station, means for
presenting a photosensitive material to said film for passage
through said printing station on the opposite side thereof from
said phototropic material, and means in said printing station fro
exposing said photosensitive material to light passing through said
phototropic material and the film whereby masked images are
presented to said photosensitive material.
2. Apparatus for masking motion picture film comprising means for
advancing the film successively through first, second and third
stations, the first station comprising density sensing means for
sensing the image contrast range of each frame of the film, the
second station comprising a mask forming station, means for
presenting a sheet of phototropic material to said film for passage
through said mask forming station in contact therewith, said mask
forming station comprising means for projecting the images of said
film onto said phototropic sheet to activate said sheet to form
masking images thereon, said latter means being controlled by said
density sensing means to provide masking images commensurate with
the film image density, the third station comprising a printing
station, means for presenting a photosensitive film to said film
for passage through said printing station in contact therewith on
the opposite side thereof as said phototropic material, and means
in said printing station for exposing said photosensitive film to
light passing through said phototropic material and the film
whereby masked images are presented to said photosensitive
film.
3. Apparatus as claimed in claim 2 wherein said phototropic
material characteristically achieves a steady state density
proportional to the intensity of the activating means.
4. Apparatus as claimed in claim 3 wherein said means in said mask
forming station for activating said sheet comprises a light source
variable in intensity, the intensity thereof being varied by said
density sensing means in accordance with the film image
density.
5. Apparatus as claimed in claim 4 comprising a memory device
operatively connected with said density sensing means and said
light source to correlate the density reading with the mask
formation in accordance with the rate of advance of the film and
phototropic material.
6. Apparatus as claimed in claim 4 wherein said phototropic
material is subject to activation by ultraviolet light, and wherein
said variable intensity light source comprises a source of
ultraviolet light.
7. Apparatus as claimed in claim 4 wherein said sheet of
phototropic material comprises a film having a length at least as
great as the film to be masked.
8. Apparatus as claimed in claim 4 wherein said phototropic
material defines a cylindrical surface, and means for rotating said
surface at the same speed as that of said film advancing means.
Description
The present invention relates generally to photographic
reproduction processes and relates more particularly to a method
and apparatus for controlling contrast in the reproduction of
photographic images from negatives or transparencies.
A well known problem in the printing of photographic transparencies
and negatives is the inability of the copy to reproduce the density
range of the negative or transparency. In black and white printing,
this necessitates the use of a technique known as "dodging" in
which light passing through the clearer areas of the negative
representing shadows or dark objects in positive is physically
restricted from some part of the exposure to the photographic
paper. In a more sophisticated and controllable method, a "shadow
mask" -- a thin diffuse positive image made on a second piece of
photographic film by contact exposure with the negative, black and
white or color -- is used to add density to the shadow or dark
areas of the negative. The effect of this mask is to selectively
restrict the light passing through these areas of the negative to
the paper thus reducing the contrast range of the image, seen by
transmitted light to one which the paper seen by reflected light,
is able to reproduce.
Color transparencies similarly have inherent high contrast and in
making duplicate transparencies or color separation negatives for
engravings or prints, "highlight masking" is an absolute necessity.
Made in the same manner as a shadow mask, a highlight mask is a
thin negative black and white image of the positive color
transparency which adds density to the highlight of lighter areas
which would otherwise "burn out" in reproduction.
The production of the described shadow and highlight masks is a
tedious and time consuming process. Care must be taken to insure an
exact registration of the processed mask when returned to the
negative or transparency and various techniques and devices are
employed to facilitate such registration. The proper exposure and
processing of the mask is in the firs instance a matter of judgment
and in many cases the mask must be remade to provide the desired
contrast correction. Accordingly, in view of its trial and error
nature, the time required for processing and drying of the mask,
the cost of materials and processing, and the problems of precise
registration, it can be understood that present masking techniques
are time consuming and expensive.
In the present invention, the contrast control during the
reproduction exposure is effected by means of a masking image
produced in a sheet of phototropic material. The sheet of
phototropic material is placed in the focal path of the negative or
transparency and serves the same masking function as the
conventional shadow mask or highlight mask referred to above.
Registration problems and processing delays are completely
eliminated with the present method and apparatus and the masking
effect is observed or measured and immediately correctable.
Phototropic or photochromic materials are those light-transmitting
materials exhibiting the phenomena wherein an exposure to radiant
energy produces a reversible change in their optical density and/or
color. The effect can be produced by the inclusion of a variety of
organic and inorganic materials in a transparent medium such as
glass or plastic. Depending upon the materials utilized to produce
the effect, the phototropic reaction may be produced by wave
lengths throughout the spectrum including infra-red, visible and
ultraviolet radiation. Reactions may be produced in which the
material becomes darker upon exposure to the activating radiation,
or in which the material becomes lighter during such exposure. In
many instances, a colorless material becomes deeply colored under
the radiation influence while conversely a colored material may
change color or become colorless during irradiation. The
phototropic effects typically are produced rather quickly and
reverse somewhat more slowly although the speed of activation and
reversal can be varied by the variation in the composition of the
phototropic materials employed, the intensity of the activating
radiation, and the use of radiation of a different wave length or
heat to accelerate the clearing of the material.
The physicochemical theories involved in the phototropic reactions
and the various classes of materials producing such effects are
known and will not be dealt with in the present disclosure. A
discussion of materials exhibiting phototropic reactions may be
found in U. S. Pat. No. 3,436,353. Other U.S. Pat. Nos. which
disclose phototropic materials include 3,197,296; 3,397,023;
3,407,145; 3,436,144; 3,454,778 and 3,476,459.
There has to date been little commercial usage of phototropic
material, its most common use being for eye glass lenses wherein
the density of the lenses increases upon exposure to ultraviolet
radiation. Other suggested applications include vehicle and
building windows, photographic lenses and filters, and
miscellaneous applications such as television tubes, instruments,
etc.
The primary suggested use of phototropic materials for photographic
purposes has been as a filter to control the amount of light
reaching the film during the photographing of a subject. In U.S.
Pat. No. 3,436,353, phototropic filters are suggested as a
substitute for the mechanically operated or photocell-operated iris
commonly in use. It is further suggested in this patent that
phototropic material may also be utilized as a coating on the
photographic film itself.
The present invention does not involve camera lenses, filters or
films utilized in recording a subject image. The invention is
specifically concerned with the density range correction required
in the reproduction of photographic images from the typical high
contrast negative or transparency.
In the present invention, a mask is formed in a sheet of
phototropic material by placing the sheet in the focal path of the
negative or transparency to be reproduced and exposing the sheet to
an activating source of radiation. Since the phototropic reaction
of certain phototropic materials including the particular material
used to date is dependent upon the intensity of the radiation
striking the phototropic sheet, the radiation passing through
lighter areas of the negative or transparency produces a more
pronounced reaction than the radiation passing through the darker
areas thereof. In the case of a negative, the reaction forms a
positive image in the phototropic material which is in perfect
registration with the negative since it was formed in place. The
mask created in this fashion is immediately utilized in the
exposure of the printing paper or film before the phototropic
reaction can reverse. Since these exposure times are conventionally
far shorter than the clearing time of the phototropic material,
there is only a negligible fading of the mask during the exposure.
Mask density may, alternately, be sustained by continuous exposure
of the mask forming material, which tends to achieve a steady state
of density relative to the intensity of the exposing light.
Due to the reversible nature of phototropic materials, the same
sheet may be repeatedly used. In a preferred embodiment of the
invention, a sheet of phototropic material is employed in place of
the lower glass element in the negative carrier of an enlarger. The
phototropic sheet may alternately be positioned on the enlarger
easel/camera back for formation of the masking image, the film or
photographic paper being placed therebeneath without changing the
position of the sheet relative to the projected image. The
invention may similarly be employed in the masking of motion
picture film utilizing the general method described which may
effectively be carried out by apparatus disclosed herebelow.
It is accordingly a first object of the present invention to
provide an improved method and apparatus for controlling image
contrast during all methods of reproduction of images from
photographic negatives, transparencies, and motion picture
film.
A further object of the invention is to provide a method and
apparatus as described which while using a masking technique
eliminates the conventional processing and registration procedures
necessary with conventional shadow or highlight masks.
An additional object of the invention is to provide a masking
method and apparatus as described in which the formation of the
mask can be observed and its density regulated as determined by the
printer's judgment or instrumentation.
Another object of the invention is to provide a method and
apparatus as described which can be carried out using conventional
equipment with a minimum amount of modification.
A still further object of the invention is to provide a method and
apparatus as described which may be effectively utilized with both
black and white and color photographic reproductions.
An additional object of the invention is to provide a method and
apparatus as described which is adapted for use in darkroom work or
in automated printing such as employed in bulk color printing of
amateur color negatives.
Still another object of the invention is to provide a method and
apparatus as described which is simpler, more economical and less
time consuming than those heretofore employed.
Additional objects and advantages of the invention will be more
readily apparent from the following detailed description of
embodiments thereof when taken together with the accompanying
drawings wherein:
FIG. 1 is a schematic front elevational view of an enlarger
constructed in accordance with the present invention;
FIG. 2 is an enlarged view partly in section taken along line 2--2
of FIG. 1 showing details of the enlarger lamphouse;
FIG. 3 is an enlarged view partly in section taken along line 3--3
of FIG. 1 showing the enlarger negative carrier;
FIG. 4 is a greatly enlarged sectional view taken along line 4--4
of FIG. 3 showing the phototropic sheet mounted in the negative
carrier;
FIG. 5 is an exploded perspective view showing the photographic
negative and the masking image thereof produced on the adjacent
phototropic sheet;
FIG. 6 is a perspective view showing schematically the manner in
which the mask can be produced exteriorly of the enlarger by
exposure of the phototropic sheet to an external radiation
source;
FIG. 7 is a schematic front elevational view of an enlarger similar
to that shown in FIG. 1 but having the phototropic element mounted
in the easel rather than the negative carrier;
FIG. 8 is a greatly enlarged sectional view taken in the circled
area of FIG. 7;
FIG. 9 is a schematic side elevational view showing apparatus for
masking motion picture film in accordance with the present
invention;
FIG. 10 is a sectional view taken along line 10--10 of FIG. 9;
and
FIG. 11 is a sectional view similar to FIG. 10 of a modified form
of the invention utilizing a phototropic film.
As indicated above, the present method and apparatus utilize a
phototropic or photochromic material to form a contrast correcting
mask. Although it is possible and within the scope of the present
invention to use a phototropic material as a masking medium which
upon activation becomes less dense for purposes of increasing
contrast in a negative or transparency, by far the more common
correction required is the decreasing of the range of the image
density. Accordingly, in each of the described embodiments a
phototropic material is employed which becomes increasingly dense
upon activation by a suitable radiation source to reduce the
contrast of the transmitted image.
The embodiments illustrated were designed to employ a commercially
available phototropic glass sold by Corning Glass Works, Corning,
New York under the name "PHOTOGRAY". This material is essentially a
silicate glass which includes silver halide crystals which are
considered to provide the phototropic effects. This glass is
sensitive to radiation in the near ultraviolet region of the
spectrum having wave lengths of approximately 3,000 to 4,000
angstroms. Although for purposes of the invention the phototropic
material may be a type sensitive to any suitable radiation source
such as light in the visible range, it is convenient to utilize a
material sensitive only to ultraviolet radiation to effect control
of the mask density.
A preferred form of apparatus for carrying out the present
invention is illustrated in FIGS. 1-4 and comprises a photographic
enlarger generally designated 12 which is largely of conventional
design. In the schematic illustration, the enlarger head 14 is
shown disposed above the baseboard 16, the usual head supporting
column and height adjusting means having been omitted to simplify
the drawings. The enlarger head includes the casing 18 enclosing
the condenser lenses (not shown) and supporting the lamphouse 20.
Secured to the lower end of the casing is an apertured plate 22. An
adjustable bellows 24 extends downwardly from the plate 22,
terminating in a lens board 26 on which is mounted the enlarging
lens 28. A negative carrier 30 is slidably received in a slot 31 in
the plate 22, as shown most clearly in FIG. 3.
Mounted in the lamphouse 20 is a conventional incandescent
enlarging lamp 32 provided with suitable socket means 34 connected
with a power source 36 by conduits 38. A timer 40 is included in
the lamp circuit as is a manually controlled switch 42. Surrounding
the incandescent lamp 32 is a circular gas discharge lamp 44, for
example, a mercury vapor lamp, adapted to produce and transmit
radiation in the near ultraviolet region of the spectrum. A
suitable socket 46 for the bulb 44 is connected by conduits 48 to
the power source 36. A timer 50 and manual switch 52 are provided
in the ultraviolet lamp circuit as well as a voltage regulator 53
for control of the intensity of the lamp output.
An easel 54 is disposed on the baseboard 16 and is of a
conventional construction including a base member 56 and a framing
assembly 58 attached thereto by hinge 60. Photographic paper is
inserted on the base member 56 beneath the framing elements of the
framing assembly which are adjusted to suit the size of the
projected image by means of the adjustment knobs 62.
The negative carrier 30 as shown in the enlarged views of FIGS. 3
and 4 includes a carrier plate 64 and a cover plate 66 of a
generally rectangular shape adapted to be superposed as illustrated
with the aid of aligning pins 68. As shown in FIG. 3, a tongue
portion 70 of the carrier extends from the enlarger when the
carrier is seated within the slot 31 of plate 22 to permit the
ready removal of the carrier from the enlarger to change or adjust
the subject negative in the carrier.
Aligned apertures 72 and 74 respectively in the carrier plates 64
and 66 permit light from the lamphouse to pass through a negative
or transparency held by the carrier to project an image thereof
onto the easel 54. To support the negative or transparency in a
flat plane perpendicular to the optical axis of the enlarger, it is
customarily sandwiched between sheets of glass which are received
by a groove 76 in the carrier sheet 64 adjacent aperture 72. In the
preferred embodiment of the invention, the lower glass sheet
comprises a phototropic glass sheet 78 which may, for example, be a
sheet of the Corning "PHOTOGRAY" glass referred to above. A
negative 80 to be enlarged is secured in flat disposition on the
phototropic sheet by the cover glass sheet 82. The sheet 83 for
convenience is attached to the carrier plate 66 while the
phototropic glass is mounted on the plate 64, thereby facilitating
the removal or adjustment of the negative 80. The described
negative carrier is entirely conventional with the exception of the
employment of phototropic glass for the negative supporting
sheet.
For operation of the apparatus shown in FIGS. 1-4, the negative 80
to be enlarged is positioned in the negative carrier 30 in the
manner illustrated and the carrier inserted in the enlarger as
shown in FIGS. 1 and 3. Prior to insertion of the printing paper
into the easel, the incandescent bulb 32 is turned on and the image
of the negative 80 is accurately focused on the surface of the
easel by adjustment of the bellows 24. The density range or
contrast of the negative is observed and may be gauged by means of
a densitometer to determine whether a mask is needed and if so, the
density of the mask required to bring the contrast range of the
transmitted image down to that of the paper.
Following the determination of the mask requirement, the
ultraviolet bulb 44 is turned on and adjusted in intensity by means
of voltage regulator 53 to activate the ultraviolet-sensitive
phototropic sheet 78 which is of a type which achieves steady state
density relative to the intensity of the activating light source.
As will be noted with reference to the schematic illustration of
FIG. 5, the light areas of the negative permit passage of the
ultraviolet light which on striking the phototropic material
activates the material to produce a positive image of the subject
negative image. As is necessary in any type of masking technique,
the masking image must be considerably less dense than the negative
or the two will tend to cancel each other out when light is
transmitted through the combined negative and mask. Any tendency of
the phototropic material to produce a slightly diffused image is
highly desirable as explained herebelow. The reverse effect is true
in the case of transparencies (positive images) wherein density is
added to the lighter (highlight) areas.
After exposure of the phototropic material to the ultraviolet light
to produce the desired density of the masking image, the
photosensitive material is inserted into the easel and the
incandescent lamp 32 is turned on to effect the exposure of the
photosensitive material through the negative 80 and phototropic
masking image. In view of the fact that most phototropic materials
reverse their reaction at a rate considerably slower than the rate
of activation, the ultraviolet light may be extinguished just prior
to the exposure of the photosensitive material since the masking
image persists for a longer period than the usual exposure time of
photosensitive materials.
If, following development of the first exposure, it should be
determined that the masking image was not of the proper density to
correct the contrast range of the negative, the procedure may be
promptly repeated, varying the density of the mask by changing the
intensity of the activating radiation. The intensity of the lamp 44
is adjusted by means of a voltage control device 53 such as a
variable transformer. As indicated above, the phototropic material
selected produces a steady state of image density dependent on the
intensity of the activating radiation source and the density of the
image produced may thus be readily varied to suit the contrast of
the negative.
The rate of activation and clearing of the phototropic glass are
dependent on a number of factors including the composition and heat
treatment of the glass. These rates are further changed
significantly by the temperature of the glass. The activation can
be accelerated by use of a high intensity source, such as pulsed
xenon, to a small fraction of a second. Similarly, the clearing
rate can be accelerated by exposure of the glass to heat or to
light of wave lengths longer than those used to activate the glass.
In the present case for example, radiant heat or sodium vapor
lighting can be used to significantly speed up the clearing rate of
the glass.
Although for convenience the apparatus of FIGS. 1 and 2 wherein the
ultraviolet source is located within the enlarger is preferred, it
will be apparent that the masking image in the phototropic glass
may alternately be produced outside of the enlarger by removal of
the negative carrier and exposure of the negative and phototropic
glass to an external ultraviolet source as schematically
illustrated in FIG. 6. After the masking image has been formed, the
negative carrier is immediately returned to the enlarger and the
exposure of the photographic paper is carried on as described
above.
A modified apparatus utilizing the same phototropic masking
principle is illustrated in FIGS. 7 and 8 and comprises an enlarger
12' similar to that described in FIG. 1. The enlarger 12' differs
only in the placement of the phototropic sheet. Instead of mounting
the sheet in the negative carrier, a large phototropic glass sheet
86 of a size sufficient to cover the photosensitive material 88 is
secured to the framing assembly 58'. The conventional clear sheets
of glass are used in the negative carrier to support the
negative.
In use, the embodiment of FIGS. 7 and 8 is operated in
substantially the manner explained above, the phototropic sheet 86
being exposed to the ultraviolet lamp following an initial
determination of the density of the mask required. The
photosensitive material 88 is positioned in the easel beneath the
sheet 86 and the exposure of the paper is made through the masking
image on the phototropic cover glass. Care must be taken not to
move the easel after making the mask since the masking image would
then not register with the projected negative image.
In view of the fact that most glass does not transmit ultraviolet
radiation, the condenser lenses of the enlargers 12 and 12' must be
made of an ultraviolet transmitting material such as quartz glass.
The cover glass sheet 82 in the negative carrier 30 of enlarger 12
must similarly be of an ultraviolet transmitting material. In the
enlarger 12' the condenser lenses, both negative carrier glass
sheets, and the enlarging lens must be capable of transmitting
ultraviolet radiation.
Since some phototropic materials will reach a steady state density
relative to the intensity of the activating radiation, the
ultraviolet lamp may remain on during the exposure of the paper if
an ultraviolet filter layer is provided on the lower side of the
sheet of phototropic material. This will eliminate the possibility
of fading of the masking image during white light exposure of the
photosensitive materials. On the other hand, it may be convenient
to make the print exposure (black and white) utilizing the
ultraviolet light source. This can be done, assuming the enlarger
optical system is adapted to transmit ultraviolet light, by first
exposing the phototropic material to form the mask, briefly
interrupting the transmission of ultraviolet to the easel during
insertion of the paper, and resuming the ultraviolet transmission
to effect the print exposure. In the event that the print exposure
is made with the ultraviolet light, only the ultraviolet bulb need
be included in the enlarger lamphouse.
As indicated above, any tendency of the phototropic masking image
to be somewhat diffuse is a desirable attribute of the present
method and will enhance the sharpness of the transmitted masked
image by adding density but not exactly matching detail. The
desirability of a diffused masking image is well known in the art
and it is common practice to use a diffusion sheet between the
image to be masked and the film to be exposed as a mask.
Depending on the characteristics of the phototropic masking
material, the mask exposure may be varied in length as well as
intensity to achieve the proper mask density. Until the material
reaches a steady state density commensurate with the light
intensity, the image density is a function of the time of exposure
to the sensitizing light source.
The apparatus described in the above embodiments are only examples
of devices which could be employed to carry out the present method.
It will be evident that different types of enlargers such as the
well known diffuser enlarger could be effectively employed to carry
out the method. Different types of enlarger light sources may also
be employed, although it is highly desirable that the phototropic
sheet activating source and the printing light source be on the
same optical axis.
From the foregoing, it will be apparent that the present method can
also be employed in masking contact exposures, for example in
making duplicates of color transparencies or negatives. The
procedure is similar to that described above except that the mask
is placed above the transparency when the duplicating exposure is
made. This can most readily be explained by a simple example
describing the preparation of a duplicate transparency. First the
transparency is affixed to the phototropic sheet with its emulsion
side facing away from the sheet. A glass cover sheet is placed over
the transparency and the assembly is exposed to an activating light
source to produce the desired masking image in the phototropic
material. The cover sheet is then removed and the duplicating
material placed in contact with the emulsion side of the
transparency. The duplicating exposure is then made from the
opposite side of the phototropic material, the exposing light
passing through the mask first, and then the transparency to the
copy. Because of the position of the mask, the masking effect may
be more diffuse than in the previously described applications, but
as indicated, this is a desirable effect.
Due to the rapid density changes possible in the phototropic
material when activated by high intensity ultraviolet radiation
such as obtained with a capacitor discharge light, the present
process is particularly adapted to the masking of motion picture
film. The process could be utilized for the high speed printing of
motion picture film master prints to release copies -- color
negative to color positive, black and white negative to positive,
color reversal to color reversal and black and white reversal
positive to reversal positive. It could also be used when film is
enlarged or reduced in size. Registration, which has been a problem
in masking motion picture film, is not a problem with the present
method since the mask remains in a fixed position relative to the
master after the masking image is formed and until the copy is
exposed.
Referring to FIGS. 9 and 10, an apparatus 90 which can for example
suitably be used for printing color positive motion picture film
from color negative film is shown. The apparatus includes a large
wheel 92 secured to a shaft 94 which is supported by and driven at
a constant speed by gear motor 96 mounted on supporting frame 98. A
film supporting sheel rim 100 made of a phototropic material
includes a flange portion 102 which is secured to the sheel 92 by
bolts 104. A cylindrical film supporting surface 108 on the rim
includes shoulders 110 and 112 respectively along the inner and
outer surface edges to guide the film along a predetermined path on
the rim.
In this instance, a master color negative film 114 to be printed is
led from reel 116 over a guide roll 118 and through a density
sensing device 120 which senses the density extremes. The need for
a mask is proportional to these extremes. The density information
for each frame is briefly stored in a memory device 122 which is
coupled to and directs a high intensity ultraviolet source 124
positioned closely adjacent the wheel rim 100. The film 114 after
passing through the density sensor 120 passes around the guide roll
126 and onto the surface 108 of the wheel rim with the emulsion
side facing away from the wheel surface. As the film passes beneath
the high intensity light source 124, the source is energized to an
intensity proportional to the film density at that frame to expose
the phototropic wheel rim thereby creating a masking image in the
rim portion beneath the surface 108. A film 130 to be exposed to
the duplicate image is supplied from a reel 132 and passed around a
guide roll 134 which leads the film in superposed relation to the
film 114 on the surface 108 with the emulsion surface thereof
against the emulsion surface of the film 114. As the wheel rotates,
the films are moved at a predetermined uniform rate past the read,
green and blue film exposure lights 136, 138 and 140 which are
mounted on the stationary bracket 142 positioned radially
interiorly of the rim portion 100. The exposure of the film 130 is
thus made through the masking image in the rim 100 and the negative
film 114. The exposed film 130 is led around the guide rolls 144
and 146 and is collected on the spool 148. The negative film 114 is
similarly led around guide roll 150 and collected on the spool 152.
Suitable means are provided to control the rotation of the spools
116, 132, 148 and 152 in accordance with the speed of movement of
the films with respect thereto.
The size of the wheel 92 is selected so that the masking image
formed in the phototropic material of which the wheel is made will
fade completely away in one wheel revolution. Should this not prove
feasible, heat or a light source of relatively long wave length can
be employed to accelerate the erasure of the masking image.
In FIG. 11 a modification of the apparatus of FIGS. 9 and 10 is
illustrated. In this embodiment, instead of the phototropic wheel
rim 100, a rim 160 of clear glass extends as an integral part of
the glass wheel 162. The masking function in this embodiment is
carried out by a thin film 164 of phototropic material which is
introduced onto the wheel rim before and removed after the film
114. The phototropic film should be at least as long as the film
being reproduced and accordingly there will be no problem of the
fading or erasing of the masking image which can be accomplished
after the reproduction exposure has been completed in any
convenient manner. The operation of the modified embodiment of FIG.
11 is essentially the same as that of FIGS. 9 and 10.
It will be apparent that the wheel arrangement illustrated is not
essential to the method described and that the several exposing
steps can be carried out utilizing a linear movement of the
juxtaposed films. For example, the masking may be accomplished by
moving the master film together with a phototropic mask forming
film past a series of slot gates, the first sensing the density of
the mask necessary, the second exposing the phototropic film
through the master, and the third gate or gates exposing the copy
through the mask and master.
In three light color printing systems the density of the mask
appropriate to each exposing color could be sensed and used to
print that particular color. Three separate masks of course could
not be employed with either of the wheel type arrangements
illustrated but could readily be adapted to the linear slot gate
system described above. In using separate masks for each color it
may be possible to utilize phototropic materials which upon
activation develop colored images.
A further application of the invention is in the so-called "camera
back" masking process. Typically carried out in a process camera,
the phototropic mask is exposed to the photographic image entering
the camera prior to insertion of the film which is placed directly
in contract with the phototropic masking material for the film
exposure.
The present invention would be particularly suited for the
production printing of color prints from amateurs' color negatives.
Each negative would be automatically scanned to measure the
extremes from light to dark and, if such scanning determined that
masking would make a better print, a phototropic mask is exposed
immediately prior to the print exposure (or a steady state density
mask exposed during the print exposure), the intensity of the
activating light being controlled by information provided by the
scanning sensors. If the photographic materials are sensitive to
the ultraviolet light which is preferably used to expose the mask,
the undersurface of the mask could be coated with an ultraviolet
absorbing filter which would not pass the ultraviolet through to
the photosensitive emulsions.
If the density achieved in a given phototropic material is not
adequate to serve the desired masking function despite variations
in activating light intensity, a phototropic masking sheet which
achieves a different density may be used. In a commercial
operation, an operator might for example have four or five
phototropic sheets available which would be graded in terms of
their attainable density range.
As indicated above, it may be possible to utilize the phototropic
mask to increase image contrast by utilization of phototropic
materials which become lighter in those areas exposed to the
activating light source.
It will be clear from the foregoing that the use of phototropic
masks is equally applicable to black and white or color negatives
as well as transparencies (color positives). Accordingly where the
term "negative" is used, it should be understood that the process
involved is equally applicable to positive and negative images,
color or black and white. With a negative, the phototrophic mask
will function as a shadow mask to hold back the darker areas of the
images, while with a transparency the mask will function as a
highlight mask to add density to lighter areas of the image.
Manifestly, changes in details can be effected by those skilled in
the art without departing from the spirit and the scope of the
invention.
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