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Claims  |
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What is claimed is: PG,51
1. An apparatus for forming a hologram for reproduction, comprising:
first computation means for receiving an input image signal representing an
object and for computing corresponding diffraction pattern data with a
first sampling density;
second computation means coupled to said first computation means, for
interpolating the diffraction pattern data to generate interpolated
diffraction pattern data with an increased second sampling density;
third computation means coupled to said second computation means, for
computing interference pattern data between the interpolated diffraction
pattern data and reference wave data; and
holographic image forming means coupled to said third computation means,
for outputting the interference pattern data to a preselected type of
output device, and for allowing reproduction of a holographic image to be
formed by controlling a generation of coherent light using the
interference pattern data.
2. The apparatus according to claim 1, wherein said holographic image
forming means comprises printer means for recording the interference
pattern data on a recording medium.
3. The apparatus according to claim 1, further comprising:
storage means connected to the first and second computation means, for
storing therein the diffraction pattern data with the diffraction pattern
data being divided into a plurality of areas.
4. The apparatus according to claim 3, wherein said storage means includes
a semiconductor page memory device.
5. The apparatus according to claim 4, wherein said semiconductor page
memory device has a memory space which permits adjacent ones of said
plurality of areas having the diffraction pattern data stored therein to
be overlapped at end 10 portions thereof.
6. The apparatus according to claim 5, wherein said second computation
means comprises:
interpolation processing means having a plurality of channels, for
effecting a predetermined type of interpolation process with respect to
said plurality of areas in said semiconductor page memory device in a
parallel manner.
7. The apparatus according to claim 6, wherein said first computation means
comprises:
programmable memory means for modifiably storing an algorithm defining a
method of computing said diffraction pattern data; and
micro-processing unit means associated with said programmable memory means,
for operating according to said algorithm.
8. The apparatus according to claim 6, wherein said third computation means
comprises:
reference light wave generator means for generating reference light data
representing a wavefront of a selected type of reference light; and
means connected to said second computation means, for computing a
fringe-shaped interference pattern data between the interpolated
diffraction pattern data and the reference light data.
9. The apparatus according to claim 8, wherein said reference light wave
generator means comprises:
programmable memory means for modifiably storing an algorithm defining a
method of computing said interference pattern data; and
micro-processing unit means associated with said programmable memory means,
for operating according to said algorithm.
10. A method for forming a hologram for reproduction, comprising the steps
of:
receiving an input image signal indicative of an object;
computing diffraction pattern data which corresponds to the input image
signal with a first sampling density;
interpolating the diffraction pattern data to generate interpolated
diffraction pattern data with an increased second sampling density;
computing interference pattern data between the interpolated diffraction
pattern and reference wave data; and
forming a holographic image by outputting the interference pattern data to
a preselected type of output device, and allowing reproduction of a
holographic image by controlling a generation of coherent light using the
interference pattern data.
11. The method according to claim 10, wherein the step of forming a
holographic image records the interference pattern data on a recording
medium by use of light beams emitted from a plurality of recording light
emitting sections.
12. The method according to claim 11, wherein the diffraction pattern data
is temporarily stored in a page memory section which is divided into a
plurality of areas.
13. The method according to claim 12, wherein adjacent ones of said
plurality of areas of the stored diffraction pattern data are overlapped
at the end portions thereof.
14. The method according to claim 13, wherein the interpolating process is
carried out for said plurality of areas in a parallel manner.
15. The method according to claim 14, wherein the steps of computing the
interference pattern data and recording the interference pattern data are
sequentially carried out in a pipeline-processing manner.
16. A hologram printing system for recording a hologram on a photographic
recording medium which produces a reproduced three-dimensional image in
space upon illumination of white light, said system comprising:
image acquisition means for receiving an object light of a
three-dimensional object and for generating a corresponding image
information signal;
first computation means connected to said image acquisition means, for
computing interference image pattern data between the object light and a
first coherent reference light of predetermined type;
real image reproduction means connected to said first computation means,
for reproducing a real image of the object by use of the computed
interference image pattern data;
second computation means for computing fringe-form interference pattern
data between the reproduced real image and a second coherent reference
light of predetermined type; and
printer means connected to said second computation means, for recording the
fringe-form interference pattern data on said recording medium.
17. The system according to claim 16, wherein said first computation means
comprises:
means connected to said image acquisition means, for computing diffraction
image pattern data with a first sampling density in response to the image
information signal;
means for interpolating the diffraction image pattern data to produce
interpolated diffraction image pattern data with an increased second
sampling density; and
means for computing pattern data and the first reference light as said
interference image pattern data.
18. The system according to claim 17, wherein said first computation means
includes:
page memory means for temporarily storing the diffraction image pattern
data having the first sampling density so that the diffraction image
pattern data is divided into a plurality of areas.
19. The system according to claim 16, wherein said printer means includes:
a multi-beam scan printer having a plurality of laser oscillators for
emitting recording light beams.
20. The system according to claim 19, wherein said multi-beam scan printer
includes:
driver means for driving said laser oscillators to cause the recording
light beams to vary in intensity according to the fringe-form interference
pattern data; and
beam-scan control means for permitting the recording light beams to move on
said recording medium in a first direction while causing said laser
oscillators to move on said recording medium in a second direction
transverse to the first direction.
21. An apparatus for forming a hologram for later reproduction using white
light, comprising:
first computation means for computing real image data indicative of an
object to generate computed real image data;
second computation means for suing the real image data as object light
data, and for computing interference pattern data between the object light
data and reference light data to generate computed interference pattern
data; and
scan-recorder means for receiving the interference pattern data, and for
recording said interference pattern data on a recording medium.
22. The apparatus according to claim 21, wherein said first computation
means comprises:
first sub-computation means for receiving an input image signal indicative
of the object, and for computing corresponding diffraction pattern data
with a first sampling density;
second sub-computation means coupled to said first sub-computation means,
for performing an interpolation for the diffraction pattern data, and for
generating interpolated diffraction pattern data having a second sampling
density being greater than the first sampling density; and
third sub-computation means coupled to said second sub-computation means,
for computing interference pattern data between said interpolated
diffraction pattern data and reference light data.
23. The apparatus according to claim 22, wherein said second
sub-computation means comprises:
fourth sub-computation means for interpolating said computed real image
data to generate an interpolated real image data having an increased
sampling density; and
fifth sub-computation means coupled to said fourth sub-computation means,
for computing interference pattern data between the interpolated real
image data and reference light data.
24. The apparatus according to claim 21, wherein said first computation
means computes the real image data using one of the group consisting of a
diffraction pattern data, an interference pattern data between a
diffraction pattern and a reference light, and a real-image reproducing
portion of the interference pattern data between the diffraction pattern
and the reference light.
25. The apparatus according to claim 22, wherein said first computation
means computes the real image data using one of the group consisting of a
diffraction pattern data, an interference pattern data between a
diffraction pattern and a reference light, and a real-image reproducing
portion of the interference pattern data between the diffraction pattern
and the reference light.
26. The apparatus according to claim 21, wherein said first computation
means includes:
one-line processing means for receiving an input image signal indicative of
the object, for applying a parallax restriction to the input image signal,
and for computing a pattern generated at a predetermined slit position of
a one line component of an object plane.
27. The apparatus according to claim 26, wherein said one-line processing
means computes the real image data using one of the group consisting of
diffraction pattern data, interference pattern data between a diffraction
pattern and a reference light, and a real-image reproducing portion of the
interference pattern data between the diffraction pattern and the
reference light.
28. The apparatus according to claim 2, wherein said printer means includes
a multi-beam scan printer having a plurality of light emitting elements
for emitting recording light beams.
29. An apparatus for forming a holographic image, comprising:
first computation means for receiving an input image signal representing an
object and for computing corresponding diffraction pattern data with a
first sampling density;
second computation means coupled to said first computation means, for
interpolating the diffraction pattern data to generate interpolated
diffraction pattern data with an increased second sampling density;
third computation means coupled to said second computation means, for
computing interference pattern data between the interpolated diffraction
pattern data and reference wave data; and
holographic image forming means coupled to said third computation means,
for forming a holographic image by controlling a generation of coherent
light using the interference pattern data.
30. The apparatus according to claim 29, wherein said holographic image
forming means comprises printer means for recording the interference
pattern data on a recording medium.
31. A method for forming a holographic image, comprising the steps of:
receiving an input image signal indicative of an object;
computing diffraction pattern data which corresponds to the input image
signal with a first sampling density;
interpolating the diffraction pattern data to generate interpolated
diffraction pattern data with an increased second sampling density;
computing interference pattern data between the interpolated diffraction
pattern and reference wave data; and
forming a holographic image by controlling a generation of coherent light
using the interference pattern data.
32. The method according to claim 31, wherein the step of forming a
holographic image records the interference pattern data on a recording
medium using the coherent light. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to holographic imaging techniques
and, more particularly, to an apparatus for forming holographic images
corresponding to input object image information for later reproduction or
reconstruction of three-dimensional (3-D) optical images. This invention
also relates to a computer-assisted hologram recording system for
computing a wave disturbance (diffraction image pattern) obtained on the
hologram recording surface based on a sampled data of a 3-D object of
interest and for recording or printing on a recording medium the pattern
of interference between the resultant diffraction pattern and reference
light.
2. Description of the Related Art
Computer holography is generally known as a technique for forming a
hologram by computing and recording the holographic image pattern of a 3-D
object on a recording medium, such as a planar holographic plate or sheet,
under the assistance of digital computer equipment. With the recent
development of digital equipment, the computer hologram recording
technique is becoming important more and more in the application field of
3-D image information processing, 3-D object measurement, 3-D display and
so forth. Particularly, the technique of forming and reproducing holograms
viewable in white light is important as stereoscopic image memory devices
in the art of computer image processing.
Unlike the existing purely optical hologram devices, the computer-hologram
apparatus produces by computation a holographic image pattern to record a
resultant computer-generated holographic image on a recording medium of
selected type. Since the computer can create any desired 3-D object images
including imaginary graphic images, the computer hologram is excellent in
flexibility and wide in applicability for industrial use. The presently
available computer hologram apparatus, however, suffers from the fact that
the efficiency of computation remains low. An increased amount of
repetitive computations should be required to produce a computer hologram.
The necessity of such repetitive computations forces the total processing
time to increase, which necessitates the use of a large-scale computer
system. This reduces the production efficiency of 3-D object hologram
which is required to be recorded to maintain the high quality of a
reproduced image.
Until today, several techniques have been proposed for reducing in amount
the image information to be processed, thereby to attain an increased
computation efficiency in the art of computer holography. One of the
techniques may be found in what is called the "Lohmann type" computer
hologram apparatus as is well known among those skilled in the art. This
computer hologram apparatus generates a hologram by computing the
diffraction pattern of an object. The computation algorithm is described,
for example, in "Precision Machine", Vol. 47, No. 12, Supplement, (Dec. 6,
1981) at pp. 101-105, wherein a computer-generated hologram is formed by
(1) inputting an object information to the computer, (2) deriving the wave
of an object on the hologram plane by computation of the diffraction image
to produce a binary-coded recording pattern, (3) creating an original
picture drawing, and (4) reducing the original picture by photographing
(completion of the hologram).
To reduce the amount of information to be computed, a hologram is created
by dividing the hologram plane into a large number of small picture points
(called "cells"), computing a diffraction pattern at the representative
point of each cell to derive the complex amplitude and phase of each
point, and giving an opening to each cell according to the computation
results. The opening given to each cell is determined as follows: the
height of opening is determined in accordance with the computed value of
the complex amplitude of a corresponding cell, whereas the positional
relation (distance) between the center of the opening and the cell center
is determined in accordance with the value of the phase. The method of
determining the size and position of the opening for each cell is
described in detail in A. W. Lohmann & D. P. Paris "Binary Fraunhofer
Holograms generated by Computer" Appl. Oct., Vol. 6, No. 10 (October 1967)
at pp. 1739-1748. An original object image can be optically reconstructed
or reproduced by applying a coherent reproducing light such as laser light
to the recorded hologram. A resultant reproduced image obtained from the
computer hologram, however, is not satisfactory in the image quality. This
is because the center of the cell opening is positionally deviated from
the representative point used as the basis for computations of phase.
Another method of creating a computer hologram is also known which is based
on the computation of a fringe-shaped interference pattern. The
interference computation type computer-generated holography is
conceptually similar to a conventional optical hologram forming scheme in
that a reference light emitted from a laser source is superposed on the
diffraction image of an object of interest to derive an interference
pattern therebetween. The recording of a hologram is performed so that the
transmissivity or the density may vary on a photographic plate in
accordance with the intensity of a resulting fringe-like interference
pattern.
According to the interference computation type computer-generated
holography, unlike the aforementioned diffraction computation type (i.e.,
Lohmann type) computer-generated holography, the phase information of a
holographic image is recorded in the interference fringe form. The phase
error can thus be minimized, which leads to enhancement of the image
quality. However, the interference computation type holography suffers
from the decreased computation efficiency due to the fact that the
decisive means for reducing the amount of information used to compute the
interference pattern has not been accomplished yet. Extra large-capacity
semiconductor memories are necessary to execute the computation for an
enormous amount of information. This results in that the scale of the
hologram recording system is increased unwantedly, which makes almost
impossible the accomplishment of a high-speed computation process with the
use of a smaller computer system. This is a serious bar to the industrial
spread of the computer hologram recording system.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a new and
improved computer hologram recording technique.
It is another object of the invention to provide a new and improved
computer hologram recording apparatus capable of enhancing the computation
efficiency while maintaining high quality of a reproduced image.
It is a further object of the invention to provide a new and improved
computer hologram recording apparatus capable of enhancing the computation
efficiency to attain a high-speed process while maintaining the high
quality of an image reproduced by use of white light.
In accordance with the above objects, the present invention is drawn to a
specific computer-assisted hologram recording apparatus which comprises a
first computation section for receiving an input image signal representing
an object and computing a corresponding diffraction pattern with a first
sampling density. A second computation section is connected to the first
computation section to subject the diffraction pattern to the
interpolation process so as to create an interpolated diffraction pattern
with a second sampling density which is thus increased. A third
computation section is connected to the second computation section to
compute an interference pattern between the interpolated diffraction
pattern and the reference wave. An output section, such as a printer or a
display device, is connected to the third computation section to either
record the interference pattern on a previously selected recording medium,
or cause the interference pattern to be displayed on the display screen of
the display device.
The foregoing and other objects, features, and advantages of the invention
will become apparent from the following more particular description of
preferred embodiments of the invention, as illustrated in the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram schematically showing the whole construction of a
computer hologram recording apparatus in accordance with one preferred
embodiment of this invention;
FIG. 2 is a diagram showing the internal construction of a
diffraction-image computation section contained in the hologram recording
apparatus of FIG. 1;
FIG. 3 is a diagram showing the internal construction of a main computation
unit contained in the diffraction image computation section of FIG. 2;
FIG. 4 is a diagram showing the internal construction of an intermediate
page memory unit contained in the diffraction image computation section of
FIG. 2;
FIG. 5 is an illustration modeling a method of performing the internal
division for a memory space of the intermediate page memory of FIG. 4;
FIG. 6 is an illustration partially indicating the diffraction pattern
which is interpolated in the main scanning direction X and the
sub-scanning direction Y;
FIG. 7 is a block diagram showing the internal construction of an
interpolation processor of FIG. 1;
FIG. 8 is a block diagram showing the internal construction of an
interference fringe pattern generator of FIG. 1;
FIG. 9 is a block diagram showing the internal circuit construction of a
reference light wave generator of FIG. 8;
FIG. 10 is a block diagram showing the internal circuit configuration of a
gradient corrector of FIG. 1;
FIG. 11 is a block diagram showing the internal construction of a
multi-beam scan recording section of FIG. 1;
FIG. 12 is a block diagram schematically showing the whole construction of
a computer hologram recording apparatus in accordance with another
embodiment of this invention; and
FIGS. 13 and 14 are block diagrams schematically showing the whole
construction of two possible modifications of the apparatus of FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, a computer hologram recording apparatus in
accordance with one preferred embodiment of this invention is generally
designated by the numeral 10. The hologram recording apparatus 10 includes
a diffraction image computation section 12, an interference image
computation section 14 and an image recording section 16. The diffraction
image computation section 12 has a function of computing a diffraction
image (diffraction pattern) information data based on a sampled input
image data representing an object of interest (20) in the hologram forming
process. The interference image computation section 14 and image recording
section 16 compute interference image information data indicative of an
interference pattern between the resultant diffraction pattern data and a
reference light data, and record the same on a preselected hologram
recording medium.
The diffraction image computation section 12 includes an input image
acquisition section 18 for receiving a sampling image data being
externally supplied thereto. The input image acquisition section 18
receives a sampling object signal Sob, which is produced by the
photoelectric conversion to represent an object of interest 20 by means of
an external photoelectric converting image photographing unit (not shown).
Alternatively, the input image acquisition section 18 may be connected to
an external computer graphics creation equipment (not shown); in such a
case, the equipment internally produces a graphic image signal Sob that
represents the object 20 without requiring any optical photographing
process of the object 20. In either case, the input image acquisition
section 18 contains a semiconductor page memory for temporarily storing
the input image signal Sob therein. The page memory will be designated by
the numeral 52 in FIG. 2.
The diffraction image computation section 12 also includes a diffraction
image processing section 22 for computing a diffraction image or pattern
and an intermediate page memory 24 which is bi-directionally communicative
with the diffraction image processor 22. The intermediate memory 24
temporarily stores therein a computed diffraction pattern information that
is output by the diffraction image processor 22 therein. The above
constituents 18, 22 and 24 are connected to an input/diffraction image
control section 26.
As shown in FIG. 1, the interference image computation section 14 includes
(1) an interpolation processing section 28 coupled to an output of the
intermediate page memory 24, (2) a processing section 30 connected to the
interpolation processor 28 to produce an interference image or pattern,
and (3) a gradient correcting section 32 connected to the interference
image generator 30. The constituents 28, 30, 32 are connected to an
interference image/recording control section 34 and operate under the
control of the controller 34. The intermediate memory 24 of the
diffraction image computation section 12 is also connected to the
controller 34. The controllers 26, 34 are associated with a main
controller 36. An input/output console section 38 is connected to the main
controller 36. The I/O console 38 includes a known keyboard unit and
display terminal such as cathode-ray tube (CRT) display terminal or a
thin-type display device, as a man-machine interface.
As shown in FIG. 1, the image recording section 16 includes a scan
recording section 40 and a hologram developing section 42 and may be a
multi-beam scanning recorder device which records or prints a finally
obtained interface pattern on the recording surface of a recording medium
44 such as a photographic plate or sheet. The plate 44 is subjected to the
developing treatment by the developer 42 to complete the printing of a
hologram. The holographic plate 44 reproduces a 3-D object image 46 upon
illumination of a reproducing reference light (not shown).
As shown in FIG. 2, the input image acquisition section 18 includes an
image data input unit 50 and a page memory unit 52 connected to the output
of it. The page memory 52 includes a memory area 54 and a memory
controller 55 associated therewith. The diffraction image processor 22
includes a diffraction pattern computation unit 56, coordinate control
unit 58 and adder 60. The computation unit 56 computes a two-dimensional
(2-D) diffraction pattern which is obtained on the hologram recording
surface with respect to each cell of the sampling input image data stored
in the page memory 52. The diffraction pattern thus computed is
sequentially supplied to a first input of the adder 60 under the control
of the coordinate controller 58. The adder 60 has an output connected to a
memory area 62 of the intermediate page memory 24. The page memory area 62
is provided in the intermediate page memory 24 together with a memory
controller 63. The intermediate page memory area 62 has a plurality of
outputs (for example, four outputs), one of which is fed back to a second
input of the adder 60.
The diffraction pattern computation unit 56 fetches data of one input cell
read out from the input page memory 52 and computes the two-dimensional
(2-D) diffraction pattern thereof. The result of that computation is
supplied to the first input of the adder 60. At this time, the second
input of the adder 60 is supplied with data read out from the intermediate
page memory 24. Data items supplied to the first and second inputs of the
adder 60 are added together and the updated result of computation appears
on the output of the adder 60. The updated result of computation is
written into the intermediate page memory 24 again. Thus, diffraction
patterns derived by the adder 60 for respective picture elements (PEL) or
cells of the input image are added together to create a diffraction
pattern which is obtained as the result of addition at every picture
element and which is kept stored in the intermediate page memory 24 for
later use.
Each picture element (cell) of diffraction image data essentially consists
of two multivalued gradient data segments which are the real part and
imaginary part of a complex number. The operations of writing the
diffraction pattern data into the intermediate page memory 24 and of
reading the data from the memory 24 are carried out sequentially and
alternately. The 2-D coordinate position control in the image space for a
series of memory access operations is effected in accordance with
coordinate data generated by the coordinate controller 58. A cell position
whereat the input image is read and a cell position of the diffraction
pattern are determined under the control of the controller 58; then, the
positional superposition of each of the diffraction patterns in the
intermediate page memory 52 is effected. As a result, final diffraction
pattern data is written into the memory area 62 of the intermediate page
memory 24.
The computation algorithm for deriving diffraction patterns of the hologram
may be determined differently depending on the type of the hologram to be
formed. For example, in a Fresnel's hologram used when the distance
between an object and the hologram plane is relatively short, the
approximate computation for a Fresnel diffraction image can be made by use
of Fresnel integrals. Alternatively, in a Fourier transform hologram used
when the distance between the object and the hologram plane is relatively
long, the approximate computation of Fraunhofer diffraction image can be
applied by use of the Fourier transform. To flexibly cope with such
different types of holograms, the diffraction pattern computation unit 56
of this embodiment is constructed by use of a micro-processing unit (MPU)
64 as shown in FIG. 3.
More specifically, the MPU 64 is connected to an internal system bus 66 of
the diffraction pattern computation unit 56 together with an input-stage
data input/output port (IOP) 68, an output-stage data IOP 70, a
control-signal IOP 72, a random access memory (RAM) 74 and a programmable
read-only memory (PROM) 76. The input IOP 68 receives an input image data
and supplies the same to the system bus 66. The output IOP 70 receives the
result of computation by the diffraction pattern computation unit 56
appearing on the system bus 66 and sends forth the same to the adder 60 of
FIG. 2. The control IOP 72 is used to receive various kinds of control
information signals that are supplied from a host control machine such as
a host computer (not shown). The PROM 76 stores therein one or a plurality
of computation algorithm software programs externally supplied via the
system bus 66. In the case of the plurality of different kinds of
algorithm software programs being stored in the ROM 76, one of the
algorithms which is optimum for the type of a presently selected hologram
can be made active in reply to an instruction from the control IOP 72.
Further, various parameters of hologram models including the positional
relation between the hologram and the object, wavelength and the like can
be externally set in the control IOP 72. The MPU 64 performs processing
operations according to the current parameter setting state in the control
IOP 72.
By way of an example, assume that the Fresnel's hologram of a
two-dimensional (2-D) object image is computed. The following algorithm is
used to derive Fresnel diffraction image data. Firstly, the 2-D image is
sampled and a set of sampled values is derived. The sampling density at
this time may be determined depending on the performance of a system
hardware actually used and/or the required quality of an image reproduced
from the hologram; in practice, the sampling density may be so selected as
to offer the resolution of approximately eight to ten dots per one
millimeter. In the above sampling process, the operation of enlarging or
reducing the 2-D image may be additionally effected; in this case, the
hologram recording apparatus 10 is so designed to have the hologram
enlarging/reducing function.
A 2-D Fresnel diffraction pattern is then computed which is formed on the
hologram plane by a light component emitted from one of a large number of
resultant sampling points is computed. A similar diffraction pattern
computation is repeatedly executed with respect to each of the remaining
sampling points. The diffraction pattern computation may be made under an
assumption that the wavefront of light emitted from a point light source
is computed. The diffraction pattern computation may alternatively be made
under an assumption that a small opening is formed in each of the sampling
points and the wavefront of light is computed which light is transmitted
through the small opening when a plane wave of an intensity corresponding
to the sampling value of the sampling point is applied to the opening from
the rear side thereof. In either of the above cases, Fresnel integrals are
used for the computation of diffraction image pattern as is well known to
the experts in the art of the computer hologram. A Fresnel diffraction
image pattern obtained from each sampling point is added to those of the
remaining sampling points to finally derive Fresnel diffraction pattern
information of the 2-D object.
The Fresnel diffraction pattern computation for a 3-D object may be
attained by expanding the above-described 2-D object processing technique
in such a manner that (1) the technique is modified to assign a sampling
value to each point of a 3-D grating so as to represent sampling values in
a 3-D space or (2) the technique is modified to represent surfaces of a
3-D object by use of a set of sampling points having respective sampling
values and add together Fresnel diffraction patterns derived from the
sampling points. If desired, removal of hidden surfaces (hidden-surface
removal) may be performed.
The diffraction pattern computation with the lower sampling density as
described above is effected automatically according to the algorithm
software program being currently selected in the PROM 76 by the MPU 64 of
FIG. 3. The computed diffraction pattern data is supplied to the
intermediate page memory 24 of FIG. 2 and stored in the memory area 62
thereof. The internal construction of the intermediate page memory 24 is
shown in detail in FIG. 4.
As shown in FIG. 4, the memory area 62 of the intermediate page memory 24
is divided into a plurality of memory blocks, for example, three memory
blocks 80a, 80b, 80c. The memory blocks 80 are associated with exclusive
address controllers 82a, 82b, 82c, respectively. The number of memory
blocks 80 is determined according to the number of pipe lines used in the
interference fringe computation and hologram recording process effected by
the interference image computation section 14 of FIG. 1. In this
embodiment, the number is set to correspond to the number of divisions of
the recording beam of the multi-beam scanning printer 40.
The three memory blocks 80a, 80b, 80c are connected to the diffraction
image processor 22 via a branched data bus 84. The memory blocks 80 are
connected to a common clock control unit 86. The control unit 86 is
supplied with a write clock signal .phi.w and a read clock signal .phi.r.
The data blocks 80 are respectively connected to three inputs of a
selector 90, which performs the data selecting operation under the control
of an output control unit 63 via data buses 88a, 88b, 88c. The selector 90
has four outputs, one of which is connected to the adder 60 of FIG. 2
through a feedback data bus 92. The remaining three outputs of the
selector 90 are connected to the interference image computation section 14
of FIG. 1 by way of respective data buses 96a, 96b, 96c.
The intermediate page memory 24 has two different operation modes. The
first operation mode is a "read modify write" mode in which diffraction
pattern addition data is read out and diffraction pattern data is written
into the same memory address. In this mode, the whole memory space of the
three memory blocks 80 is regarded as a sheet of page memory and the
entire memory address control is effected by the address memory control
units 82. The second operation mode is a "separate read/write" mode,
wherein the three memory banks 80 are independently accessed by the
respective address control units 82 and diffraction pattern data items
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