Note: Descriptions are shown in the official language in which they were submitted.
-- 7968 216903~
Title: Spatial Light Modulator Assembly for Adapting a
Photographic Printer to Print Electronic Images
Background of the Invention
The present invention relates generally to a spatial light modulator assembly used
in combination with a photographic printer and, more particularly, the invention
relates to a spatial light modulator assembly which is adapted to fit in a negative
holder in a photographic printer replacing a photographic negative thus allowing the
5 photographic printer to print electronic images onto photographic paper located
therein.
A photographic printer is used in a photofini.~hing center in combination with a
film developer. The film developer is used to develop a latent image on conventional
film into a photographic negative. The photographic negative is then placed in a
o photographic printer where the negative is backlit to project image-bearing light onto
the photographic paper to effect exposure of the photographic paper. The image
projected onto the photographic paper is selectively reduced or enlarged with respect
to the negative image depending upon a choice of lens systems located between the
photographic negative and the photographic paper.
In such a photographic printer, each time a new negative image is to be imaged
onto photographic paper, the negative must be mechanically or physically manipulated
into a proper position such that the projected image is in ~lignment with an exposure
plane of the photographic paper. Such physical manipulation can be costly in terms of
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production time. Large photofiniching labs known as macrolabs automatically
manipulate negatives but the systems themselves have a cost in the range of hundreds
of thousands of dollars and are, therefore, prohibitively expensive for many
applications.
With the advent of electronic imaging cameras, a need has arisen to allow
electronic still camera users to be able to print electronically recorded images onto
photographic paper. This is currently accomplished by printing the electronically
recorded images through a computer to a ~llm recorder attached thereto. A problem is
that a cost of buying a computer and a film recorder to simply print electronically
recorded images from the electronic still camera is prohibitive.
With many conventional film photofini~hing centers, minilabs and macrolabs,
distributed throughout the world, it is desirable to allow a user of the electronic still
camera to bring an electronic image storage medium or transmit electronic image
signal to the photofini~hing center for printing the electronically recorded image onto
photographic paper. Thus, the image generated by the electronic still camera would
be printed onto photographic paper to create a conventional hard copy photographic
image in a way similar to that of conventional film.
Therefore, it is an object of this invention to provide an adapter to enable
conventional film photographic printer to print electronically recorded images.
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It is another object of the invention to provide an adapter that is easily inserted
into a photographic printer in a minilab, or the like, to convert the minilab into an
electronic image printing system and thereafter easily remove the adapter to convert
the minilab back into a conventional film photofini~hing system.
s It is still another object of this invention to decrease an amount of physical
manipulation required to place photographic images upon photographic paper.
It is still another object of the invention to decrease a cost of generating hard copy
photographic images for individual users of electronic still cameras.
It is a further object of this invention to inexpensively adapt conventional film
lo photofini~hing systems to record electronic image signal on photographic paper.
These and other objects of the invention will be obvious and will appear
hereinafter.
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Sllmm~ry
The aforementioned and other objects are achieved by the invention which
provides an extremely versatile apparatus for adapting a conventional photographic
printer to print electronically recorded images on photographic paper. The apparatus
s comprises computer means, and a spatial light modulator assembly which removably
replaces a photographic negative in the conventional photofini~hing system when the
photofini~hing system is to be used to print electronically recorded images.
In non-electronic image printing operation, the conventional photographic
development system operates to emit a beam of light through an aperture in a negative
lo holder which hoids a photographic negative having an image recorded thereon. The
light beam is then altered by the recorded image to produce image-bearing light. The
image-bearing light passes through an optical system, which includes a lens system to
focus the image-bearing light, and a shutter to govern an amount of time the image-
bearing light is projected onto the photographic paper to form a photographic image.
In electronic image printing operation, the photographic negative is removed and
replaced with a spatial light modulator assembly which receives electronic image
signal from the computer means.
The computer means reads electronic image data from an electronic image
storage medium or receives the electronic image data from an external source such as
20 distant computer network, for example. The computer means then processes and
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transmits the electronic image signal to the spatial light modulator assembly which
comprises an adapter and spatial light modulation means.
The adapter is constructed to be removably and replaceably inserted into the
negative holder of the conventional photographic printer in place of the photographic
5 negative, thus allowing conversion between electronic image printing operation and
non-electronic printing operation.
The spatial light modulation means is enclosed by the adapter and is electrically
connected to said computer means. In response to the electronic image signal
transmitted from the computer means, an image is imprinted on the spatial light
lo modulation means to form a transparency thereon. The spatial light modulation
means selectively allows the beam of high intensity light to pass therethrough altering
the beam to produce image-bearing light. After passing through the lens system, the
image-bearing light renders the image upon the photographic paper.
In further aspects, the invention provides methods in accord with the apparatus
5 described above. The aforementioned and other aspects of the invention are evident
in the drawings and in the description that follows.
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Brief Description of the Drawings
The foregoing and other objects of this invention, the various features thereof, as
well as the invention itself, may be more fully understood from the following
description, when read together with the accompanying drawings in which:
sFigure 1 shows a perspective view of a photographic printer system according
with the embodiment of the present invention;
Figure 2 shows an exploded view of individual components of the photographic
printer system of Figure 1; and
Figure 3 is an exploded view of a negative carrier and spatial light modulator
oassembly in accordance with the invention as shown in Figure 1.
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Detailed Description
While the present invention retains utility within a wide variety of photographic
printing systems and can be embodied in several different forms, it is advantageously
employed in connection with a minilab photographic printer. Though this is the form
5 of the preferred embodiment and will be described as such, this embodiment should
be considered illustrative and not restrictive.
Figure 1 depicts a minilab photographic printer for use with the present invention.
A minilab 10 is a term commonly used in the industry to describe small semi-
automated photofinishing centers having photographic developers and photographic
lo printers. The present invention can also be used with amateur systems where the
photographic printer is not automated and also with highly automated macrolabs
without detriment to the invention.
The rninilab 10 shown includes a lamp house 12 for housing a light origin~ting
device. Above the lamphouse is a cut filter 14 which determines the colors to be
15 imaged upon the photographic paper. Light from the lamphouse 12 having passed
through the cut filter 14 is then tr~ncmit~ed through a light tunnel 16 which has
mirrored sides to optimize transmission of light up to a negative carrier 18.
The negative carrier 18 is designed for use with conventional photographic
negatives such that the photographic negative slides into the negative carrier and is
20 held securely in place while various colors of the light pass therethrough.
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In electronic im~ging, a negative is not produced. Instead, the image is captured
and stored as electronic image signals. The electronic image signals are then
transmitted to a spatial light modulator ("SLM") assembly 20 which is inserted into
the negative carrier 18 in place of the photographic negative.
The SLM assembly 20 has information that is sent from a computer 24 having a
driver card (not shown) inserted into the computer 24. Typically, the SLM assembly
20 accepts one of standard television or VGA signals. In the preferred embodiment,
the driver card is a VGA display card well known in the art tr~n~mitting a VGA
signal.
lo The computer 24 can receive the aforementioned electronic image signals from
any of various sources including, but not limited to, an electronic still camera, a
magnetic or optical storage device, or directly from an electronically transmitted
signal source. The computer 24 processes this information and transmits a processed
image signal through a cable 22 to the SLM assembly 20. Based upon the content of
the processed image signal, the SLM assembly 20 selectively alters a tr~ncmit~nce of
each pixel in a matrix of pixels and thus forms an image thereon to allow image-
bearing light to selectively pass through portions of the SLM assembly 20
representative of the image which is imprinted on the SLM assembly 20.
The image-bearing light having passed through the SLM assembly 20 then goes
into a lens system 26 which determines an amount of enlargement or reduction of the
~ ~ 7968 2~6~033
image based upon a lens or lenses contained in the lens system 26. The lens system
can contain a single lens or multiple lenses depending upon the implementation of the
photographic printer.
A shutter unit 28 above the lens system 26 controls an exposure time. The shutter
5 unit 28 selectively opens to allow image-bearing light to pass through a shutter
contained therein to expose photographic paper. A paper mask 30 is shown above the
shutter assembly which isolates individual frames of the photographic paper such that
exposure is restricted to a predetermined area of the photographic paper.
The individual components of the minilab io are shown in more detail in Figure 2,
o and will be referred to with continuing reference to Figure 1.
The light origin~ting device held within the lamphouse 12 is a lamp 32 which is
often a halogen-type high-intensity lamp. To reduce heat produced by the lamp 32
that reaches subsequent portions of the system, a piece of heat reflecting glass 34 is
located above the lamp 32.
Light from the lamp 32 then passes through a series of three dichroic filters 36.
The three dichroic filters representing yellow, magenta, and cyan are individually
adjustable by adjusting knobs 38 and are adjusted once for each time the lamp 32 is
changed. Such an adjustment is necessary to compensate for individual color
characteristics of the lamp 32.
~ 7968 ~1690~3
Another set of color filters, the cut filter 14, are located above the dichroic filters
36. A yellow filter 40is selectively movable into a path of light above the dichroic
filters 36. A magenta ~1lter 42 and a cyan filter 44 are also selectively movable into
the light path such that individual colors or a sum of 2 or 3 colors of light can be
s projected onto the photographic paper.
The colored light having passed through the filters is now conducted by the mirror
tunnel 16. The mirror tunnel 16 is essentially an elongated rectangular box lined with
light reflecting mirrors such that substantially all light passing into the mirror tunnel
16 is tr~n~mitted out a top portion of the mirror tunnel 16.
The colored light emitted from the mirror tunnel 16 then passes through a diffuser
46 which redistributes the light to form a uniform light distribution over an area of the
spatial light modulator or negative.
The colored light emitted from atop the diffuser 46 is then passed through a
negative carrier 18 which has an aperture in its center for allowing light to pass
15 therethrough and has opposed clamping portions for holding a photographic negative
in position above an aperture. Where the photographic negative has now been
replaced by the SLM assembly 20 of the invention, the colored light passes through
the aperture to illuminate an imaging area of the SLM assembly 20 which selectively
transmits portions of the colored light to create image-bearing light.
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'~ 7968 216903~
In an alternative embodiment of the invention, the negative carrier 18 is replaced
with a SLM carrier which performs a similar function to that of the negative carrier 18
and has an aperture size larger than the standard negative carrier 18 but still smaller
than an area of the diffuser 46. This allows more light to pass through into the SLM
s assembly 20 which can now have greater dimensions than that of a standard film
format, a 35 mm negative, for example.
The light passing through the SLM assembly 20 creates the image-bearing light
which then passes into the lens system 26 cont~ining an enlarging lens 48. One
skilled in the art will realize that the enlarging lens 48 can be replaced by multiple
lenses in the lens system 26 and can be used for reducing, transmitting, or enlarging
the image.
The enlarging lens 48 determines an amount of enlargement of the image onto
photographic paper. A standard set of lenses for the conventional photographic
printer includes lenses to enlarge a photographic negative to standard photograph sizes
of 3l/2"x 5 ", 4" x 6" 5 " x 7 " Along with an amount of enlargement, the lens itself is
chosen dependent upon a thickness and dimensions of a negative or, in this case, the
SLM assembly 20. If the SLM assembly 20 is thicker or has different dimensions
than the conventional photographic negative then the enlarging lens 48 must be
changed or an additional lens must be added to accommodate the dimensional
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`` 7968 ~16~033
difference. For thickness changes, the lens is changed to accommodate a
displacement of focal planes of the negative versus the SLM assembly 20.
In one embodiment of the invention, the thickness and dimensions of the SLM
assembly 20 are chosen to accommodate the standard lens sizes, in that the thickness
5 and dimensions are substantially identical to that of the photographic negative.
Alternatively, the thickness and dimensions are chosen to ensure that most of the
standard lenses are utilized. For example, a thicker or dimensionally larger SLM
assembly is chosen such that the use of the standard 4" x 6"1ens results in a print size
of 3l/2"x 5 "and the 5 " x 7 "lens results in a print size of 4" x 6 "
lo In a second embodiment of the invention, the enlarging lens 48 and the SLM
assembly 20 are manufactured into one optical system 26. Inserting this optical
system 26 automatically converts the minilab into an electronic image processing lab
without additional changes required. In a third embodiment of the invention, the color
filters 40, 42, 44 are also included into a single optical system as described above.
In either case, the image-bearing light having passed through the enlarging lens 48
is then presented upon a shutter 52. The shutter 52 is housed within the shutter unit
28 and is connected to a solenoid 50. The solenoid 50 is an assembly which is used as
a switch, consisting essentially of a coil and a metal core free to slide along a coil axis
under the influence of the magnetic field so as to selectively drive the shutter 52 to
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7968 2169033
open and close. Thus, the shutter controls an amount of the image-bearing light
passing therethrough. An amount of time that the shutter 52 is allowed to remain
open determines exposure time of the image-bearing light onto photographic paper 54.
The photographic paper 54 is held within the paper mask 30 such that the image-
5 bearing light is restricted to a selected area on the photographic paper producing apositive image thereon.
A fourth embodiment of the invention has the SLM assembly 20, the enlarging
lens 48, and the shutter unit 28 manufactured into one optical assembly. This allows
greater control over the im~ging process by the computer 24 as the computer 24 can
10 now control exposure time.
In practice, the computer 24 feeds the electronic image signal to the photographic
printer 10 in three distinct steps. The original electronic image signal is divided into
three color planes corresponding to red, green and blue. The red color plane is loaded
into the SLM assembly 20 and the photographic paper 54 is then exposed through the
s SLM assembly 20, the magenta filter 42, and the yellow filter 40 for a desired amount
of time. Only red sensitive layers of the photographic paper 54 are now exposed.
Next the green color plane is loaded into the SLM assembly 20 and the
photographic paper 54 is exposed through the SLM assembly 20, the yellow filter 40
` 7968 2169~33
and the cyan filter 44. Thus the photographic paper 54 is now exposed for both the
red and green sensitive layers.
Finally, the blue color plane is loaded into the SLM assembly 20. The
photographic paper 54 is exposed through the SLM assembly 20 and the cyan filter 44
s and the magenta filter 42.
All three layers of the photographic paper are now exposed in red, green and blue
and the paper is then ready for chemical processing.
Referring now to Figure 3, the negative carrier 18 and the SLM assembly 20 are
shown in detail. The SLM assembly 20 includes as major components an adapter 58
10 and an SLM 60. The adapter 58 is designed to mechanically interconnect with the
negative carrier 18 such that the adapter 58 is held firmly in position during
photographic imaging. The adapter 58 has opposed grooves 64 that adapt a thickness
of the SLM assembly 20 down to an approximate thickness of a photographic
negative. This allows the adapter 58 to pass freely through the negative carrier 18 so
15 that the SLM assembly 20 can be removably and replaceably inserted into the
photographic printer 10. One skilled in the art will realize that various other
mechanical interconnections can be utilized for differing models of the photographic
printer.
7968 2169~33
In the preferred embodiment, the SLM 60 is an active matrix spatial light
modulator that is a liquid crystal matrix of individual pixels which are each selectively
changeable between light tran~mis~ive and light blocking states in gradll~tçd steps
called gray levels. The SLM 60 has a matrix of 1024 by 1440 pixels each
5 incorporating 256 gray levels to provide a resolution similar to that of high definition
television. Those skilled in the art appreciate that an exposure can be achieved with
an SLM matrix which has more or less pixels than that described and with more or
less gray levels impacting only a look of the final printed image and not the invention
itself.
While the number of pixels in the matrix is determined by the properties of
available SLM's, the gray levels are dependent also upon a driver from the computer
24. In the preferred embodiment, a commercially available 8-bit VGA driver board is
used to generate 256 shades of gray at the output of the SLM 60. These shades of
gray are nonlinearly spaced with respect to numerical representations of digital inputs
15 to the VGA driver board. This nonlinear relationship is designed for direct display to
the human eye, and therefore, is appropriate for viewing but not for printing since eye
characteristics are different than characteristics of photographic paper. Specifically,
the 256 evenly spaced levels generated by the VGA driver board to drive the SLM
translate to 256 non-evenly spaced optical densities on the photographic paper with a
20 poor quality of print as a result.
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To transform this system to a high quality print, at least 8 bits, i.e. 28 = 256, evenly
spaced optical densities must be produced onto the photographic paper. Mapping an
8-bit output through a non-linear function presents multiple maps to input points
between integer input values. Rounding the input value reduces print quality and,
s therefore, is avoided. Tn~te~tl, 10 to 12 bit linearly spaced exposure values are used to
compensate for the nonlinear characteristic of the paper. To achieve the 10 to 12 bit
linearly spaced exposure values with 8-bit VGA board driving the SLM 60, multiple
exposure lS used.
The simplest form of a multiple exposure is a binary exposure. For example, 10-
0 bits per color requires exposing the film 10 times per color plane. Each exposure insequence would have to be two times longer than the previous exposure. Only a one-
bit (i.e. two gray levels) SLM system would be necessary, but print speed would be
slower unless the shutter speed is very fast to accommodate the shortest exposure
time. This can require changing a shutter in the photographic printer.
To increase print speed without changing the shutter, a number of bits exposed at
a given time could be increased. But, multiple exposures other than binary require a
linear exposure system. The nonlinear characteristics of the SLM 60 can be linearized
by applying a look-up table ("LUT") to the digital image signal to yield a linear
exposure system.
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In the preferred embodiment in which the print speed is important and the shutter
speed cannot be increased beyond a fixed maximum speed without replacing the
shutter, only two exposures per color, 5 bits each, is utilized to achieve 10 equally
spaced exposure levels. The linearizing LUT in front of the 8-bit VGA board is
s programmed such that the 5 bits (25 = 32 equally spaced numbers) at the input of the
composite exposure system correspond to 32 linearly spaced tr:~n~mitt~nces of the
SLM. This creates a linear exposure system.
During the printing, first, the 5 least significant bits are used to make a first
exposure. Subsequently, the next 5 bits, or most significant bits, are applied to the
exposure system. The second exposure lasts 25 = 32 times longer. That way a 10-bit
resolution linear exposure system is achieved with 8-bit nonlinear SLM system and a
double exposure per color.
One skilled in the art will realize from the above description that other
combinations of number of exposures and bits in the exposures can be used as long as
5 their sum adds to 10. For example, a 5-bit exposure followed by five binary
exposures could be used.
Surrounding the SL~I active area is a rim 62 of matrix electronics which govern
individual addressing of the pixels within the matrix. The matrix electronics are in
turn controlled by the computer 24. The cable 22 is held in position in the adapter by
20 a conduit 66.
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The SLM assembly 20 slides into the negative carrier 18 such that the grooves 64
pass under clamping portions 70 of the negative carrier 18 and into alignment with an
aperture 68 such that light passing through the aperture 68 is allowed to pass through
the active area of the spatial light modulator 60 to create image-bearing light.
The invention may be embodied in other specific forms without departing from
the spirit or essential characteristics thereof. The present embodiments are, therefore,
to be considered in all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the foregoing
description, and all changes which come within the m(~ning and range of equivalency
of the claims are therefore intended to be embraced therein.
