Artificial retina cell, artificial retina and artificial visual apparatus

An artificial retina cell effectively used to recognize a plurality of objects from an image containing them with ease and at high speed. Also disclosed are an artificial retina and an artificial visual apparatus employing the same. The artificial visual apparatus includes an artificial eyeball (3) having a focusing means (2) and an artificial retina (1) including a first artificial retina cell disposed in a central visual field (1a) to detect a bright-dark boundary by optical filtering and a second artificial retina cell disposed in a peripheral visual field (1b) to detect an object position by optical filtering, and a neural network (4) for executing pattern recognition of an object on the basis of information detected by the first artificial retina cell. The apparatus further includes a means for determining an object to be recognized subsequently from information detected by the second artificial retina cell of the artificial retina (1), and a means (5) for moving the artificial eyeball (3) toward the object to be recognized. Thus, a specific object in an image containing a plurality of objects of recognition is selectively recognized with ease and at high speed.

BACKGROUND OF THE INVENTION 
The present invention relates to an artificial retina cell, artificial 
retina and artificial visual apparatus, which are effective for 
recognition of objects from an image containing them. 
Scenes which are seen in our daily life, that is, natural images, each 
contain a large number of objects to be recognized. We unconsciously 
recognize them before thinking, judging or acting. It is said that in the 
recognition process a position where the contrast suddenly changes in the 
image, that is, a boundary between bright and dark regions, is detected by 
the early visual mechanism, and the detected information is sent to the 
brain in the post-stage where the object concerned is recognized. As shown 
in FIG. 15, the early visual mechanism is composed of visual cells 111, 
horizontal cells 112, and bipolar cells 113. The mechanism will be briefly 
explained below. First, when an image enters the early visual mechanism, 
only the visual cells 111 that receive the light are excited. The 
excitation is transmitted to the horizontal cells 112, which constitute a 
layer underlying the visual cells 111. Each horizontal cell 112 are 
planarly connected to about 6 adjacent horizontal cells 112, and the 
excitation is transmitted through this connection. Therefore, the 
excitation of the surrounding horizontal cells 112 changes gently as if it 
were transmitted through a network. The bipolar cells 113 are each 
connected to a visual cell 111 and a horizontal cell 112 and are excited 
in accordance with the difference in excitation intensity between these 
two cells 111 and 112. The excitation is further transmitted to the 
underlying layer. Finally, the excitation reaches the brain where 
recognition of the object and feature extraction are executed. 
In actuality, when a boundary between bright and dark regions, such as the 
contour of an object, is considered as an image, the excitation intensity 
of the visual cells 111 in the early visual mechanism first changes 
rapidly, as shown by the curve A in FIG. 16(a). On the other hand, the 
excitation intensity of the horizontal cells 112 changes gently, as shown 
by the curve B in FIG. 16(a). Accordingly, the bipolar cells 113 are 
excited only at the boundary between bright and dark regions in accordance 
with the difference in excitation intensity between the cells 111 and 112, 
as shown by the curve C in FIG. 16(b), and the information on the boundary 
between bright and dark regions is transmitted to the brain where 
recognition processing is executed. 
C. A. Mead et al. with the University of California constructed an early 
visual mechanism having the bright-dark boundary detecting function in the 
form of an electric circuit and experimentally produced it as a chip (see 
C. A. Mead and M. A. Mahowald, "A Silicon Model of Early Visual 
Processing", Neural Networks, vol. 1, pp. 91-97 (1988)). As shown in the 
partly enlarged circuit diagram of FIG. 17, the device of C. A. Mead et 
al. is composed of photodiodes 201, resistance networks 202 each 
comprising 6 resistors which connect the center and vertexes of a hexagon, 
and amplifiers 203. The photodiodes 201 function as visual cells, the 
resistance networks 202 as horizontal cells, and the amplifiers 203 as 
bipolar cells. At a boundary between bright and dark regions of an image, 
the voltage of the photodiode 201 changes stepwisely. On the other hand, 
the node voltage of the resistance network 202 changes gently. In 
accordance with the voltage difference, the voltage of the amplifier 203 
changes only at the boundary between bright and dark regions. The changes 
in voltage of these elements are similar to the changes in excitation 
intensity of the cells shown in FIG. 16. Accordingly, the boundary between 
bright and dark regions, that is, the contour of the object, can be 
detected in the same way as in the case of the human early visual 
mechanism. 
K. G. Birch proposed a technique of optically detecting a boundary between 
bright and dark regions, although it is not directly conscious of the 
early visual mechanism (see K. G. Birch, "A Spatial Frequency Filter to 
Remove Zero Frequency", OPTICA ACTA, vol. 15, No. 2, pp. 113-127 (1968)). 
According to this method, the zero-order light component is cut off in the 
spatial frequency domain, thereby detecting a boundary between bright and 
dark regions in the image. If the proposed method is associated with the 
early visual mechanism, it may be interpreted as follows. For 
simplification, only the one-dimensional direction is considered with 
reference to FIG. 18. Information on light and dark in the image is 
represented by .phi.(x) (see FIG. 18(a)). If the light-dark information 
.phi.(x) is Fourier-transformed and passed through a filter 
{1-rect(.xi./b)} that cuts off the zero-order light component, 
EQU F{.phi.(x)}.multidot.{1-rect(.xi./b)} (1) 
(see FIG. 18(b)) In the above expression, F{ } represents a Fourier 
transform, and rect(x) is defined by 
##EQU1## 
Further, b in rect(.xi./b) is determined so that the zero-order peak of 
the diffraction pattern is substantially cut off by {1-rect(.xi./b)}. The 
inverse Fourier transform f(x) of the expression (1) is given by 
EQU f(x)=.phi.(x)-.phi.(x)*sin c(x/b) (2) 
where * represents convolution, and sinc(x) is given by 
EQU sin c(x)=sin (x/2)/(x/2) 
f(x) is obtained by subtracting .phi.(x)*sinc(x/b) blunted by the 
convolution from the light-dark information .phi.(x), as shown in FIG. 
18(c). It will be understood by comparison of the expression (2) with FIG. 
16 that the first term .phi.(x) of the expression (2) is similar to the 
response of the visual cells, while the second term .phi.(x)*sinc(x/b) of 
the expression (2) is similar to the response of the horizontal cells, and 
f(x) is similar to the response of the bipolar cells. Thus, their methods 
can be said to be one way of representing the human early visual 
mechanism. Further, since the optical processing handles the intensity in 
actual practice, the processed image is expressed as 
.vertline.f(x).vertline..sup.2, as shown in FIG. 18(d). Thus, the 
bright-dark boundary is obtained as a dark line sandwiched between a pair 
of light lines. 
The above-described prior art device and method for detecting a bright-dark 
boundary suffer, however, from the following problems. The device of Mead 
et al. is suitable for integration and miniaturization which may be 
achieved by the existing LSI manufacturing technology, but it involves an 
unavoidable electrical delay of the constituent elements. Therefore, the 
processing speed is relatively low. The method of Birch, which adopts an 
optical arrangement, is an excellent method that makes use of the inherent 
high-speed and parallel nature of light. In actual practice, however, this 
method cannot readily be realized because of the difficulty in attaining 
the required alignment between the constituent elements and low 
reliability with respect to temperature, vibration, etc. Accordingly, 
there is a demand for an inventive idea for enabling a bright-dark 
boundary to be optically detected with ease and at high speed. 
The prior art device and method for detecting a bright-dark boundary make 
good use of the principle of the human early visual mechanism, and it is 
certain that the prior art device and method can realize recognition of a 
boundary line between bright and dark portions of a single object in an 
image. However, it is difficult for them to recognize an image containing 
a plurality of objects of recognition. The reason for this is that when 
the input image contains bright-dark boundary information on a plurality 
of objects, it is necessary to recognize each bright-dark boundary after 
segmenting the information into pieces of information for the respective 
objects. Although image recognition in a case where the number of objects 
contained in the input image is limited to one can be realized, for 
example, by a simple associative memory on a neural network. However, 
considerably advanced and complicated processing is needed for the 
segmentation of information for each object. It is not easy even for a 
neural network to realize such processing. Thus, a novel idea is needed to 
realize recognition of an image containing a plurality of objects to be 
recognized. 
SUMMARY OF THE INVENTION 
In view of the above-described circumstances, it is a first object of the 
present invention to provide a first type artificial retina cell, a second 
type artificial retina and an artificial visual apparatus which can 
optically detect with ease and at high speed a bright-dark boundary in an 
image that is necessary for recognition of an object in the image and for 
feature extraction, and also provide a method of producing the same. 
It is a second object of the present invention to provide a visual 
artificial retina which has both the above-described first type artificial 
retina cell and a second type artificial retina cell different from the 
first type artificial retina cell, which are needed to recognize with ease 
and at high speed a plurality of objects from an image containing them, 
and also provide an artificial visual apparatus that employs the visual 
artificial retina. 
As has been described above, it will be apparent that it is appropriate for 
recognition of an object in an image to apply the information processing 
principle of the human early visual mechanism and to utilize the 
bright-dark boundary information. The present invention also utilizes the 
bright-dark boundary information for the recognition processing. More 
specifically, the present invention employs the following first type 
artificial retina cell. That is, as shown in FIG. 1, the first type 
artificial retina cell includes a Fourier transform lens 10 which forms a 
Fourier transform image of information, which is focused on an input 
surface 9 defined by one lens end surface, on an approximately planar end 
surface at the side reverse to the input surface 9, and a filter 11 that 
is formed in close contact with the approximately planar end surface of 
the Fourier transform lens 10, which is reverse to the end surface defined 
as the input surface 9. The first type artificial retina cell further 
includes an inverse Fourier transform lens 13 which has an approximately 
planar end surface brought into close contact with the filter 11 and which 
forms an inverse Fourier transform image of the filtered information as 
information of real domain on an output surface 12 defined by the other 
end surface thereof. As the filter 11, a spatial frequency filter that 
cuts off the zero-order light component of the Fourier transformed 
diffracted light is employed. As will be clear from the above explanation, 
the first type artificial retina cell of the present invention is composed 
of optical elements. Therefore, the detection of a bright-dark boundary 
necessary for recognition of an object in the image can be effected in 
parallel and at high speed. Further, in the first type artificial retina 
cell of the present invention, a lens having an approximately planar end 
surface, e.g., a gradient index lens, is employed as each of the Fourier 
and inverse Fourier transform lenses 10 and 13. Accordingly, it is 
possible to make alignment between the constituent elements on the basis 
of the lens end surfaces. In addition, it becomes unnecessary to effect 
swing & tilt and alignment in the direction of the optical axis. 
The method of producing the first type artificial retina cell according to 
the present invention will be explained below. The zero-order light 
cut-off portion 11a of the filter 11 in the first type artificial retina 
cell directly influences the detection of a bright-dark boundary and 
requires the highest degree of alignment accuracy. To provide the 
zero-order light cut-off portion 11a so as to extend in directions 
perpendicular to the optical axis (i.e., directions of axes .xi. and .eta. 
in FIG. 1) with a high degree of alignment accuracy, a method is adopted 
wherein an approximately planar exit end surface of the Fourier transform 
lens 10 which is reverse to the input surface 9 is defined as a filter 
surface 40, and the filter 11 is formed directly on the surface 40 with 
high accuracy, as shown in FIG. 6. The specific filter forming procedure 
will be explained below. First, a positive resist material, for example, 
is coated on the filter surface 40, and after prebaking, a parallel beam 
of light 41 is applied at right angles to the input surface 9. At this 
time, a diffraction pattern appears on the filter surface 40, resulting 
from the presence of the input surface 9 that acts as an aperture. 
However, most of the light converges on a light beam converging portion 
42, as shown in FIG. 6, where the intensity is extremely higher than that 
in the other portion. The light beam converging portion 42 exactly 
coincides with the zero-order light component, which is desired to cut off 
by the filter 11. The period of time for irradiation with the light beam 
41 is set so that only the light beam converging portion 42 is 
sufficiently exposed. Next, the resist is developed. Since it is a 
positive resist, only the portion corresponding to the zero-order light 
component, which has sufficiently been exposed, dissolves in the 
developer, while the other portion remains. Thus, the patterning process 
is completed. Further, a light-shielding material, e.g., a metal film, is 
attached to the zero-order light cut-off portion by vapor deposition or 
other similar method, and the resist portion is lifted off by an organic 
solvent. Thus, the zero-order light cut-off portion 11a of the filter 11 
can be formed as a light-shielding film. The zero-order light cut-off 
portion 11a of the filter 11 directly influences the detection of a 
bright-dark boundary. With this method, however, since the filter 11 is 
directly formed by using the actual light beam for each individual lens to 
be used, the alignment accuracy, including the influence of an error in 
production of the lens itself, is improved by a large margin. Accordingly, 
the filter 11 can readily be formed with sufficiently high alignment 
accuracy to serve as a bright-dark boundary detecting filter for an 
artificial retina cell. It should be noted that the filter 11 may be 
provided on the input surface of the inverse Fourier transform lens 13 
instead of being provided on the Fourier transform lens 10. It is also 
possible to use a silver salt photosensitive emulsion in place of the 
resist. 
Thus, it will be understood that the method of producing the first type 
artificial retina cell makes it possible to solve the problems associated 
with the prior art method of Birch, that is, difficulty in attaining the 
required alignment accuracy, and low reliability with respect to 
temperature, vibration, etc., and to obtain readily an artificial retina 
cell capable of detecting a bright-dark boundary with sufficiently high 
accuracy to carry out a pre-processing function for recognition of an 
object. 
Further, the first type artificial retina device according to the present 
invention has, as shown in FIG. 9, a focusing means 2 for transmitting 
information on an object O in an image, which is an object of recognition 
or feature extraction, to the above-described first type artificial retina 
cell. The artificial retina device has a plurality of first type 
artificial retina cells 6 arranged in parallel. The device further has a 
detecting means 8 for detecting information focused on the output surface 
12 (see FIG. 1) at the back of the artificial retina cell 6. 
With the above-described arrangement, the first type artificial retina 
device of the present invention can take information on an object at any 
position into the first type artificial retina cell with a desired size 
and detect a bright-dark boundary at high speed. Alternatively, the object 
information may be transmitted to a post-processing unit, for example, a 
neural network. In such a case, the system needs to be designed as 
follows: 
That is, a first type artificial retina cell 6 is disposed in a central 
visual field 1a defined in the central portion of the artificial retina, 
and a zero-order light cut-off spatial frequency filter is used as the 
filter of the artificial retina cell 6. With this arrangement, a 
bright-dark boundary in the input image is detected, and the detected 
information is sent to the neural network in the post-stage to recognize 
the object (see FIGS. 4 and 12). It should be noted that the range of the 
first type artificial retina cell 6, that is, the central visual field 1a, 
is limited to a relatively small region on the artificial retina so that 
the artificial retina cell 6 recognizes approximately one object in the 
corresponding region in the input image. Accordingly, the recognition 
function can be realized by a relatively simple neural network as 
described above. 
However, with the above-described arrangement, it is only possible to 
recognize one piece of object information that happens to be present in 
the central visual field 1a, but it is impossible to realize recognition 
of a plurality of objects in the input image containing them, which is the 
second object of the present invention. Therefore, it is desired to move 
the central visual field 1a to the position of information on another 
object of recognition in some way. For this purpose, it is necessary to 
determine the position of an object outside the central visual field 1a. 
Accordingly, the visual artificial retina according to the present 
invention has second type artificial retina cells 7 which are disposed in 
a peripheral visual field 1b defined outside the central visual field 1a. 
The second type artificial retina cells 7 are arranged in the same way as 
the first type artificial retina cell 6. That is, as shown in FIG. 3, each 
second type artificial retina cell 7 includes a Fourier transform lens 10 
which forms a Fourier transform image of information, which is focused on 
an input surface 9 defined by one lens end surface, on an approximately 
planar end surface at the side reverse to the input surface 9, and a 
filter 11 that is formed in close contact with the approximately planar 
end surface of the Fourier transform lens 10, which is reverse to the end 
surface defined as the input surface 9. The second type artificial retina 
cell further includes an inverse Fourier transform lens 13 which has an 
approximately planar end surface brought into close contact with the 
filter 11 and which forms an inverse Fourier transform image of the 
filtered information as information of real domain on an output surface 12 
defined by the other end surface thereof. As the filter 11, a higher-order 
light cut-off spatial frequency filter having a higher-order light cut-off 
portion 11c is employed. With this arrangement, only a low-frequency 
component in the input image, that is, an approximate shape of an object, 
is detected, and the position of the object in the peripheral visual field 
1b is detected by using the detected information on the shape of the 
object. 
Next, the central visual field 1a must be moved to a subsequent object of 
recognition by using the information from the second type artificial 
retina cells 7. Accordingly, an artificial eyeball 3 is composed of a 
visual artificial retina 1 such as that shown in FIG. 2, and a focusing 
means 2 for transmitting information on an object in an image, which is an 
object of recognition, to the visual artificial retina 1, as shown in FIG. 
4. With this arrangement, the position of an object to be recognized 
subsequently is determined from the information detected by the second 
type artificial retina cells 7, and the artificial eyeball 3 is moved by 
an artificial eyeball moving means 5 that moves the central visual field 
1a to the subsequent object of recognition. 
The above-described arrangement will be explained below more specifically 
with reference to FIG. 4. The artificial visual apparatus of the present 
invention transmits information on an image containing a plurality of 
objects of recognition to the visual artificial retina 1 through the 
focusing means 2, takes approximately one object in the image information 
into the central visual field 1a of the artificial retina 1 to detect 
information on a bright-dark boundary of the object, and sends the 
information to the neural network 4 in the post-stage where object 
recognition is executed (in the illustrated example the bright-dark 
boundary of a triangular portion in the image is detected). At the same 
time, an approximate shape of an object other than the object presently 
recognized is detected in the peripheral visual field 1b of the visual 
artificial retina 1. Further, the position of an object to be recognized 
subsequently is determined by the artificial eyeball moving means 5. Upon 
completion of the recognition of the object presently recognized, the 
central visual field 1a is moved to the determined position where 
recognition of the subsequent object is executed. In FIG. 4, a square 
portion, for example, is selected as an object to be recognized 
subsequently, and the central visual field 1a is moved toward the selected 
object in the image (see FIG. 5). The described operation is repeatedly 
carried out. Thus, the artificial visual apparatus behaves like a human 
being that looks around for an object of recognition by moving the 
eyeball. As will be clear from the foregoing description, the first 
artificial retina cell of the present invention includes a Fourier 
transform lens having an approximately planar exit surface and forming a 
Fourier transform image of information input through an entrance surface 
thereof on the exit surface, and a filter provided in close contact with 
the exit surface of the Fourier transform lens to cut off at least a 
zero-order light component in the Fourier transform image. The first 
artificial retina cell further includes an inverse Fourier transform lens 
that has an approximately planar entrance surface which is provided in 
close contact with the filter, and that forms an inverse Fourier transform 
image of information input through the entrance surface. 
The second artificial retina cell of the present invention includes a 
Fourier transform lens having an approximately planar exit surface and 
forming a Fourier transform image of information input through an entrance 
surface thereof on the exit surface, and a filter provided in close 
contact with the exit surface of the Fourier transform lens to cut off 
higher-order light components in the Fourier transform image. The second 
artificial retina cell further includes an inverse Fourier transform lens 
that has an approximately planar entrance surface which is provided in 
close contact with the filter, and that forms an inverse Fourier transform 
image of information input through the entrance surface. 
In these artificial retina cells, it is practical to use a gradient index 
lens as each of the Fourier and inverse Fourier transform lenses. 
The first artificial retina of the present invention includes an artificial 
retina cell, and an element for detecting output light from the artificial 
retina cell. The artificial retina cell includes a Fourier transform lens 
that forms a Fourier transform image of an input object image on a 
predetermined plane, and a filter disposed on the predetermined plane to 
cut off a zero-order light component in the Fourier transform image. The 
artificial retina cell further includes an inverse Fourier transform lens 
that returns the filtered Fourier transform image to the form of 
information of real domain by inverse Fourier transformation. 
Preferably, the Fourier transform lens of the artificial retina cell has 
approximately planar entrance and exit surfaces, and the Fourier transform 
image is formed on the exit surface. Further, the filter is disposed in 
close contact with the exit surface. In addition, the inverse Fourier 
transform lens of the artificial retina cell has approximately planar 
entrance and exit surfaces. The entrance surface is disposed in close 
contact with the filter. The inverse Fourier transform lens is disposed so 
that the inverse Fourier transform image is formed on the exit surface. 
The second artificial retina of the present invention includes a first type 
artificial retina cell, a second type artificial retina cell, and an 
element for detecting output light from the first and second type 
artificial retina cells. The first type artificial retina cell includes a 
Fourier transform lens that forms a Fourier transform image of an input 
object image on a predetermined plane, a filter disposed on the 
predetermined plane to cut off a zero-order light component in the Fourier 
transform image, and an inverse Fourier transform lens that returns the 
filtered Fourier transform image to the form of information of real domain 
by inverse Fourier transformation. The second type artificial retina cell 
includes a Fourier transform lens that forms a Fourier transform image of 
an input object image on a predetermined plane, a filter disposed on the 
predetermined plane to cut off higher-order light components in the 
Fourier transform image, and an inverse Fourier transform lens that 
returns the filtered Fourier transform image to the form of information of 
real domain by inverse Fourier transformation. 
Preferably, the Fourier transform lenses of the first and second artificial 
retina cells each have approximately planar entrance and exit surfaces, 
and the Fourier transform image is formed on the exit surface. Further, 
the filter is disposed in close contact with the exit surface. In 
addition, the inverse Fourier transform lenses of the first and second 
artificial retina cells each have approximately planar entrance and exit 
surfaces. The entrance surface is disposed in close contact with the 
filter. Each inverse Fourier transform lens is disposed so that the 
inverse Fourier transform image is formed on its exit surface. 
The artificial visual apparatus of the present invention includes an 
artificial eyeball having means for forming an object image and an 
artificial retina including the above-described first and second type 
artificial retina cells. The artificial visual apparatus further includes 
a neural network for executing pattern recognition of an object on the 
basis of information detected by the first type artificial retina cell of 
the artificial retina, means for determining an object to be recognized 
subsequently from information detected by the second type artificial 
retina cell of the artificial retina, and means for moving the artificial 
eyeball toward the object to be recognized. 
The present invention also includes a method of producing an artificial 
retina cell, wherein a photosensitive material is coated on an 
approximately planar exit surface of a Fourier transform lens that forms 
on the exit surface a Fourier transform image of information input through 
an entrance surface thereof, and a beam of plane light is made incident on 
the entrance surface of the Fourier transform lens for a desired period of 
time so as to expose only a portion corresponding to a zero-order light 
component in the Fourier transform image formed on the exit surface. Then, 
the exposed portion is provided with a light-shielding means, and an 
inverse Fourier transform lens, which has an approximately planar entrance 
surface and forms an inverse Fourier transform image of information input 
through the entrance surface, is brought into close contact at its 
entrance surface with the light-shielding means. 
According to the present invention, an artificial retina cell is provided, 
and an artificial retina is constructed by using the artificial retina 
cell. By using the artificial retina, it is possible to selectively 
recognize a specific object in an image containing a plurality of objects 
of recognition with ease and at high speed. 
Still other objects and advantages of the invention will in part be obvious 
and will in part be apparent from the specification. 
The invention accordingly comprises the features of construction, 
combinations of elements, and arrangement of parts which will be 
exemplified in the construction hereinafter set forth, and the scope of 
the invention will be indicated in the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the artificial retina cell, artificial retina and 
artificial visual apparatus according to the present invention will be 
described below. 
First embodiment: 
This embodiment relates to the artificial retina cell according to the 
present invention. As shown in FIG. 1, the Fourier transform lens 10 and 
the inverse Fourier transform lens 13 of the first type artificial retina 
cell for constituting an artificial retina are each formed by using a 
gradient index rod lens having a diameter of 1 mm, a 1-pitch length of 
12.8 mm, a numerical aperture of 0.38 and a center refractive index of 
1.557. The lens is used with a pitch length of 0.25. The term "1-pitch 
length" of the gradient index rod lens is the length required to form an 
image of the entrance end surface on the exit end surface as an erect 
image after forming it as an inverted image once halfway between the two 
end surfaces. The gradient index rod lens constituting the Fourier 
transform lens 10 has an approximately flat surface as a focal surface at 
the side reverse to the input surface 9. An aluminum film is formed on a 
portion of the approximately flat surface which has a diameter smaller 
than about 2 .mu.m as a zero-order light cut-off portion (11a in FIG. 1) 
for detecting a bright-dark boundary by the above-described method of 
producing a filter by passing the actual light beam. In addition, an 
aluminum film is formed on a portion of the approximately flat surface 
which has a diameter larger than about 50 .mu.m as a higher-order light 
cut-off portion (11b in FIG. 1; in this embodiment, it cuts off about 
30th- and higher-order light components) for eliminating noise by an 
ordinary mask patterning process, thereby forming a filter 11. Next, the 
gradient index rod lens as the Fourier transform lens 10 formed with the 
filter 11 and the gradient index rod lens as the inverse Fourier transform 
lens 13 are bonded together, thereby forming a first type artificial 
retina cell (central visual field cell) 6. 
For example, when a letter T as shown in FIG. 7(a) (the inside of the T, 
shown by black, is light) is input to the input surface 9 of the 
artificial retina cell, a T which is light only at the double-line 
portion, as shown in FIG. 7(b), appears on the output surface 12. The 
region between the pair of light lines represents the bright-dark 
boundary. 
Second embodiment: 
In the second embodiment, the Fourier transform lens 10 and the inverse 
Fourier transform lens 13 are each formed by using a lens block comprising 
25 unit lenses arranged in a square configuration at a pitch of 0.4 mm, as 
shown in FIG. 8 (the figure shows a sectional view taken along the plane 
including the optical axis for simplification). Each unit lens comprises a 
gradient index planar micro-lens having a diameter of 0.2 mm, a focal 
length of 1 mm and a numerical aperture of 0.1. Each gradient index planar 
micro-lens in the Fourier transform lens 10 has a flat filter surface 40 
defined by a focal plane thereof. An aluminum film is formed on a portion 
of the filter surface 40 which has a diameter smaller than about 8 .mu.m 
as a zero-order light cut-off portion 11a for detecting a bright-dark 
boundary by the same filter producing method as in the first embodiment. 
Further, an aluminum film is formed on a portion of the filter surface 40 
which has a diameter larger than about 65 .mu.as a higher-order light 
cut-off portion 11b (in this embodiment, it cuts off about 10th- and 
higher-order light components) for eliminating noise by an ordinary mask 
patterning process, thereby forming a filter 11. Next, the gradient index 
planar micro-lens as the Fourier transform lens 10 formed with the filter 
11 and the gradient index planar micro-lens as the inverse Fourier 
transform lens 13 are bonded together, thereby forming a first type 
artificial retina cell. In this embodiment also, a light double line such 
as that shown in FIG. 7(b) appears, and the region between the pair of 
light lines represents the bright-dark boundary. Although in this 
embodiment the double line is discontinuous because of the coarse lens 
pitch, it is not an essential problem because the influence of the 
discontinuous double line can be minimized by reducing the lens pitch 
and/or increasing the number of unit lenses used. 
Although in the first and second embodiment the filter 11 is formed with 
the higher-order light cut-off portion 11b, it should be noted that this 
portion 11b is provided for elimination of noise from the input image and 
hence not essential. Accordingly, the filter 11 may comprise the 
zero-order light cut-off portion 11a alone. Further, although in FIGS. 1 
and 8, which illustrate the first and second embodiments, respectively, 
both end surfaces of each lens used are shown to be planes, it should be 
noted that only the surfaces of the Fourier and inverse Fourier transform 
lenses 10 and 13 which are closer to the filter 11 need to be 
approximately planar and that the surfaces reverse to these surfaces need 
not be approximately planar. 
Third embodiment: 
Next, an artificial retina is formed by using the first type artificial 
retina cell as shown in FIG. 1 or 8. That is, as shown in FIG. 9, the 
artificial retina has a focusing means 2 for transmitting information on 
an object O in an image, which is an object of recognition or feature 
extraction, to the first type artificial retina cells 6. The first type 
artificial retina cells 6 process the transmitted information and extract 
bright-dark boundary information therefrom. The artificial retina further 
has a detecting means 8 for detecting the bright-dark boundary information 
extracted by the first type artificial retina cells 6. The detecting means 
8 may further transmit the detected information to a post-processing unit 
that executes recognition or other advanced processing. With this 
arrangement, it is possible to readily realize a system whereby 
information on an object at any position is taken into the artificial 
retina with a desired size, and a bright-dark boundary is detected by the 
above-described processing. The detected information may be further 
transmitted to a post-processing unit, e.g., a neural network. 
More specifically, as shown in FIG. 9, 63 artificial retina cells of the 
first embodiment are arranged on and bonded to a 2/3-inch CCD (about 6.6 
mm and about 8.8 mm in length and breadth) with 420,000 pixels, which is 
used as the detecting means 8 (in the figure the number of artificial 
retina cells is reduced for simplification). Further, a zoom lens for VTR 
is used as the focusing means 2, thereby forming an artificial retina. For 
example, when a triangle (the inside of the triangle, shown by black, is 
light) is input to the artificial retina as the object O, as shown in the 
figure, a double-line triangle as shown in FIG. 10(a) is obtained from the 
2/3-inch CCD with 420,000 pixels, serving as the detecting means 8. The 
region between the pair of lines represents the bright-dark boundary. If a 
linear sensor having 10.times.10 (total of 100) pixels is used in place of 
the CCD and a threshold of a certain level is set, a rough bright-dark 
boundary is obtained as a signal of bright dots (see FIG. 10(b)). 
If the bright-dark boundary information from the detecting means 8 of the 
artificial retina is input to a neural network, it is possible to effect 
further advanced recognition of an object in the input image or further 
advanced feature extraction, as a matter of course. 
Fourth embodiment: 
This embodiment relates to a visual artificial retina comprising the first 
and second type artificial retina cells 6 and 7. The first type artificial 
retina cell 6 employed in this embodiment is the same as that in the first 
embodiment. The second type artificial retina cell 7 is the same as the 
first type artificial retina cell 6 of the first embodiment except for the 
filter 11. The filter 11 used in this embodiment has an aluminum film 
formed on a portion thereof that has a diameter larger than about 17 .mu.m 
as a higher-order light cut-off portion (11c in FIG. 3; in this embodiment 
it cuts off about 10th- and higher-order light components) by an ordinary 
mask patterning process. As the detecting means 8 (see FIG. 2), a 2/3-inch 
CCD (6.6 mm and 8.8 mm in length and breadth) having 380,000 pixels is 
employed. One first type artificial retina cell 6 is disposed in an 
approximately central portion of the detecting means 8, and 62 second type 
artificial retina cells 7 are arranged in the other portion of the 
detecting means 8 in a matrix comprising 7 columns and 9 rows. 
For example, when an image such as that shown in FIG. 11(a) (in which 
portions shown by black are light, while portions shown by white are dark) 
is input to the visual artificial retina, a double-line triangle is 
obtained in the central portion of the CCD serving as the detecting means 
8, as shown in FIG. 11(b) (the region between the pair of lines is the 
bright-dark boundary), and image information representative of approximate 
information on other objects is obtained in the peripheral portion of the 
CCD. Although in this embodiment the filter 11 of the first type 
artificial retina cell 6 is formed with the higher-order light cut-off 
portion 11b, it should be noted that this portion 11b is provided for 
elimination of noise from the input image and hence not essential. 
Accordingly, the filter 11 may comprise the zero-order light cut-off 
portion 11a alone. Further, although in FIGS. 1 to 3 both end surfaces of 
each lens are planar, it should be noted that the reason for this is to 
simplify the alignment required to set up the system. Thus, the surfaces 
of the Fourier and inverse Fourier transform lenses 10 and 13 which are 
closer to the filter 11 need to be approximately planar, but the surfaces 
reverse to these surfaces need not always be approximately planar. 
Further, although the input and output surfaces 9 and 12 are set on the 
lens end surfaces for the same reason as the above, it is not always 
necessary to do so if it is allowed to slightly sacrifice the readiness of 
alignment. In addition, it will be apparent that an artificial retina 
having the same effectiveness as the above can be obtained by using 
gradient index planar micro-lenses as shown in FIG. 8 in place of the 
gradient index rod lenses. 
Fifth embodiment: 
This embodiment relates to an artificial visual apparatus that makes use of 
the visual artificial retina of the fourth embodiment. FIG. 12 shows the 
arrangement of the artificial visual apparatus. Referring to the figure, 
an artificial eyeball 24 is composed of a zoom lens 21, a visual 
artificial retina cell unit 22, and a detecting unit 23 comprising a CCD 
image sensor. These constituent elements are accommodated in a single 
housing. The artificial eyeball 24 is movably provided so that the visual 
field can be changed with respect to a desired object. An object image is 
formed on the entrance surface of the visual artificial retina cell unit 
22 by the zoom lens 21. The CCD image sensor 23 receives the object image 
through the artificial retina 22 and converts the image pattern into an 
electric signal. As shown in FIG. 13, the CCD image sensor 23 has about 
770.times.490 pixels in breadth and length, and the entire screen is 
divided into 63 regions in 9 columns and 7 rows. A first type artificial 
retina cell 6 as shown in FIG. 1 lies in a portion corresponding to the 
central region of the CCD image sensor 23, and second type artificial 
retina cells 7 as shown in FIG. 3 are disposed in a portion corresponding 
to the remaining peripheral region. The output signal from the CCD image 
sensor 23 is converted into a digital signal in an A/D converter 25 and 
then input to a computer 26. Among the input image information, 
information on the central portion is input to a neural network 27 for 
pattern recognition, and the other information is used for detection of 
peripheral information. 
As shown in FIG. 14, the neural network 27 has an input layer 80, a hidden 
layer 90, and an output layer 100. 85.times.70 pieces of image information 
in the central region of the CCD image sensor 23, which corresponds to the 
first type artificial retina cell 6, are supplied to respective input 
units 81, 82, . . . of the neural network 27. With these pieces of image 
information, signals representative of an object pattern are output to 
output units 101, 102, . . . through intermediate units 91, 92, . . . 
Since the neural network 27 has been previously allowed to learn objects 
of recognition according to the back propagation rule by presenting them 
in the central visual field 1a, the shape of the object can be 
discriminated by the output signal from the neural network 27. The signal 
representative of the object shape is supplied to a subsequent step 28 
where necessary information processing is further executed. 
When there is no object image in the central region, or when another object 
is to be discriminated after recognition of an object in the central 
region, the peripheral information is used. The peripheral information is 
supplied to an integrating-judging means 29 where brightness is integrated 
for each region and the integrated value is compared with a predetermined 
threshold. If the integrated value exceeds the threshold value, it is 
judged that an object is present in the region concerned. The judgment 
information is supplied to an object selecting means 30. The object 
selecting means 30 selects one region from among regions judged that an 
object is present therein at random on the basis of a random number 
generated from a random number generating means 31. A signal 
representative of the selected region is supplied to an artificial eyeball 
driving means 32 to change the direction of the eyeball 24 so that the 
selected object comes in the center of the visual field. 
Thus, it is possible to select objects to be recognized successively from 
an image containing a plurality of objects of recognition and discriminate 
them from each other for recognition. 
When an object cannot be recognized by the neural network 27, the size of 
the image taken in the visual field is changed by varying the 
magnification of the zoom lens 21, and recognition process is executed 
once more. By doing so, it is possible to cope with such a situation that 
the desired object cannot be contained within the central visual field or 
it is too small, or another object interferes with the recognition. 
It will be apparent that a two-dimensional map can be drawn on the image by 
combining together information obtained from the neural network 27 and 
information on the positions of objects obtained by the second type 
artificial retina cells 7. Further, a combination of two artificial visual 
apparatuses according to the present invention can be applied to 
recognition of a three-dimensional image. It is a matter of course that 
the neural network 27 is not necessarily limited to the neural network of 
the type having a layered configuration and employing the back propagation 
rule, which is used in the described embodiment, and that it is possible 
to employ any type of neural network which can be used in the manner of an 
associative memory model, e.g., Hopfield model, Associatron, etc. If 
information obtained from the neural network 27 is further transmitted to 
a post-processing unit, as shown in the figure, further advanced 
processing can be executed, as a matter of course. 
According to the present invention, the artificial retina cells are 
composed of optical elements. Therefore, it is possible to effect 
recognition of object information, segmentation thereof and position 
detecting processing in parallel and at high speed. Since lenses having 
approximately planar end surfaces are employed, the constituent elements 
can be aligned with each other on the basis of the lens end surfaces, and 
it is unnecessary to effect swing & tilt and alignment in the direction of 
the optical axis. Further, the zero-order light cut-off portion of the 
filter, which directly influences the bright-dark boundary detecting 
function and which requires the highest degree of alignment accuracy and 
hence bottlenecks facilitation of the construction of the system, is 
formed by using the actual light beam. Accordingly, the alignment accuracy 
of the zero-order cut-off portion can be improved by a large margin. Thus, 
the system can readily be realized. 
In the artificial visual apparatus of the present invention, the artificial 
retina is divided into two portions having different functions, that is, 
the central visual field and the peripheral visual field, so that the 
central visual field recognizes approximately one object at a time. 
Accordingly, a pattern recognizing means (neural network or the like) that 
executes recognition processing can be arranged in a considerably simple 
structure. In addition, a portion which is to be recognized subsequently 
is determined on the basis of information obtained from the peripheral 
visual field, and the central visual field is directed to the portion to 
be recognized by the operation of the artificial eyeball moving mechanism. 
Accordingly, a plurality of objects in the input image can be recognized 
by the neural network without changing the simple arrangement thereof. 
Although the artificial retina cell, artificial retina and artificial 
visual apparatus of the present invention have been described by way of 
the embodiments, it should be noted that the present invention is not 
necessarily limited to the described embodiment and that various changes 
and modifications may be imparted thereto.