Parallel analog device for the local processing of a bidimensional signal

An analog parallel device for the local processing of a bidimensional signal comprises an input means, a processing means and an output means, the input means receiving the bidimensional signal and supplying, on a group of elementary input points organized in matrix-like manner, a group of parallel electrical input signals, the processing means receiving said input signals and supplying, on a group of elementary output points organized in matrix-like manner, a group of parallel electric output signals, each of which is obtained by a linear or non-linear combination of a plurality of input signals, the output means receiving said output signals, said means being realized in the form of thin films on a substrate. This device may be particularly applied to local image processing.

BACKGROUND OF THE INVENTION 
The present invention relates to a parallel analog device for the local 
processing of a bidimensional signal. This processed signal can be 
optical, electrical, acoustic or of some other nature. 
In the case where the signal received is a bidimensional optical signal, 
i.e. an image, the device according to the invention can be advantageously 
used in numerous fields including medical imaging, robotics (recognition 
of shapes), videocommunications (compression of information), meteorology, 
etc. In the case of an acoustic bidimensional signal, the device according 
to the invention can be used for carrying out processing, such as of an 
acoustic histogram. 
The local processing of a bidimensional signal is carried out by a means 
receiving, in parallel, a group of component signals organized in 
accordance with a matrix of p rows and n columns (in which p&gt;1 and n&gt;1) 
and supplying, in parallel, a group of component signals organized in the 
same way, where each output component signal is a function of the input 
component signal of the same rank in the matrix and input component 
signals in the vicinity of said input component signal. 
The function connecting an output component signal to a group of input 
component signals is called the processing operator which can be linear or 
non-linear. A window defines the number of input component signals 
contributing to an output component signal. 
In the case where the bidimensional signal is an optical signal, the device 
makes it possible to carry out processing operations such as smoothing, 
noise elimination, contrast increase, a detection of contours, patterns or 
textures, etc. 
Throughout the remainder of the text, attention will essentially be 
directed at devices for the local processing of an image (in the 
conventional sense it is therefore a bidimensional optical signal). It is 
obvious that this example is taken for illustration purposes, whereas the 
invention applies to all such signals, no matter what their nature. 
A description will now be given of the main local image processing means 
according to the prior art. These devices can be classified in two 
categories, namely digital devices and analog devices. 
Local image processing is mainly performed by digital devices. This 
processing, performed on a conventional computer, is slow because the 
number of elementary operations is high and approximately 10.sup.6 for a 
320.times.320 point image with a 3.times.3 point window. Thus, for 
example, the local processing of a 512.times.512 point image on a Digital 
Equipment PDP 11 mini-computer takes approximately 30 seconds calculation. 
In order to reach processing speeds compatible with the speed of a video 
signal supplying 25 images per second in accordance with European 
standards or 30 images per second in accordance with U.S. and Japanese 
standards, it is necessary to either use a very powerful computer, or 
special systems of the parallel processor or systolic machine type. These 
different systems suffer from the disadvantage of being very complex to 
realize and program, whilst also being very onerous. 
In addition, devices for the analog local processing of an image are know. 
In principle, these devices require a very high parallelism, because there 
is a simultaneous processing of all the points of the image. These devices 
are produced either with the aid of discrete components, or by assembling 
integrated circuits each processing about 100 image points. Thus, these 
devices cannot be used for processing normal sized images, i.e. having at 
least 10.sup.5 image points, due to the number of discrete components or 
the number of integrated circuits which would be necessary, the complexity 
of their assembly and their cost. 
SUMMARY OF THE INVENTION 
The object of the present invention is to obviate the disadvantages of the 
known type. This object is achieved by a parallel analog local processing 
device in thin film form. This technology offers a very high processing 
speed making it possible to process in real time video signals, such as 
television signals. Moreover, this thin film technology is used in known 
manner for realizing matrixes of transistors for addressing flat-faced 
screens. Thus, this technology is suitable for the processing of images 
having 10.sup.5 or more elementary points. In addition, this technology 
offers the advantage of lending itself to mass production and therefore to 
the production of a processing device at low cost. Finally, the 
realization of the processing device in the form of thin films permits its 
integration into image recording or plotting means, such as solid cameras 
or flat-faced screens. 
More specifically, the present invention relates to a device for the 
parallel analog local processing of a bidimensional signal comprising an 
input means, a processing means and an output means, the input means 
receiving the said bidimensional signal and supply on a group of 
elementary input points organized in matrix-like form, a group of parallel 
electric input signals, the processing means receiving said input signals 
and supplying on a group of elementary output points organized in 
matrix-like manner, a group of parallel electric output signals, each 
electric output signal being obtained by the linear or non-linear 
combination of a plurality of input signals, the output means receiving 
said output signals, said means being reali edzin the form of thin films 
on a substrate. 
The number of elementary output points is generally equal to the number of 
elementary input points. However, in certain special cases, these numbers 
can differ. 
According to a preferred embodiment, the processing of each input signal is 
limited to one spatial window of a given size. 
In preferred manner, for the processing of a bi-dimensional optical signal, 
the input means has a photo-conductive layer. 
In preferred manner, for the processing of a bi-dimensional electrical 
signal, the input means has an addressing matrix. 
According to a preferred embodiment, the output means has a display means, 
which can e.g. be a liquid crystal display. This permits a direct display 
of the processed bidimensional signal. 
According to another preferred embodiment, the output means comprises an 
addressing matrix. In a preferred manner, the processing means comprises 
at least one resistive layer and a group of layers alternatively having 
insulating layers and groups of etched conductive lines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates the structure of the processing device according to the 
invention. This device is constituted by an input means, a processing 
means and an output means in the form of thin films on a substrate. 
Thus, on substrate 2 are successively arranged a group of layers forming 
the input means 4, a group of layers forming the processing means 6 and a 
group of layers forming the output means 8. 
Input means 4 receives the bidimensional signal to be processed. This 
signal can be of a random nature, e.g. optical, electrical, acoustic or of 
some other type. It can be in the form of a series signal, e.g. a video 
signal received in the form of an electrical signal, or in parallel form, 
e.g. an optical image. The function of the input means 4 is to convert 
this bidimensional signal received into a group of parallel electrical 
signals organized in matrix-like manner. These parallel signals are 
supplied to a group of elementary conductive points 10 organized in 
matrix-like manner and constituting the intermediate layer between the 
input means 4 and the processing means 6. 
Thus, the processing means 6 receives an electrical image formed from a 
group of points representing the bi-dimensional signal received by the 
input means 4. On a group of elementary conductive points 12 organized in 
matrix-like manner, it supplies another electrical image, which is deduced 
from the electrical image received by applying a mathematical operator to 
each point of said image received. This processing is of a local nature, 
i.e. the electrical signal received by an elementary output point 12 is a 
function of the signal supplied by the elementary input point 10 of the 
same rank and same column in the matrix and by the signals supplied by the 
elementary points 10 close to the latter. 
In the known local processing devices, the size of the processing window is 
often 3.times.3 (the signal supplied by an elementary output point 12 is 
then a function of signals supplied by an elementary input point 10 and 
its eight neighbours). The size of the window is limited in the known 
devices, because the time necessary for calculating an image varies in 
accordance with the square of the window. 
Conversely, the device according to the invention has the remarkable 
feature that the time for calculating an image is independent of the size 
of the window. This constitutes a supplementary advantage of the 
invention, because the use of a window of a larger size generally permits 
a finer processing of the image. 
It is important to point out that although in general the number of 
elementary output points 12 is equal to the number of elementary input 
points 10, as shown in FIG. 1, there is no reason why a processing means 
should not be produced in which the number of elementary output points is 
larger or smaller than the number of elementary input points. The number 
of elementary output points can e.g. be smaller than the number of 
elementary input points in applications such as information compression. 
The electrical image processed by the processing means 6 is received by the 
output means 8. The latter has the function of converting the electrical 
image received into a bidimensional signal of a type and form adapted to 
the envisaged processing. Output means 8 can in particular carry out a 
conversion which is the reverse of that carried out by input means 4. 
According to a first preferred embodiment, output means 8 performs an 
electrooptical conversion of the electrical image supplied by processing 
means 8. This conversion can e.g. be performed by a display incorporating 
a liquid crystal film. 
It is known that liquid crystals are rapidly degraded, because they are 
subject to a d.c. voltage. It is therefore obvious that in an embodiment 
of the device according to the invention in which the processing means has 
a liquid crystal film, the input means 4 must supply at each elementary 
input point 10 an electrical signal of zero mean value, e.g. an a.c. 
voltage signal. 
According to another preferred embodiment of the device according to FIG. 
1, the output means 8 has an addressing matrix making it possible to 
multiplex the electrical signals supplied by each of the elementary output 
points 12, in order to transmit the processed image in the form of a frame 
of a video signal. 
A description will now be given in exemplified manner of a first embodiment 
of the processing device according to the invention, in which the 
mathematical processing operator is a linear operator and a second 
embodiment of the processing device according to the invention in which 
the mathematical operator is non-linear, but can be expressed with the aid 
of two linear operators. As will be shown hereinafter, these linear 
functions can easily be represented in the processing means 6 by a 
resistive layer. 
Thus, the processing device according to the invention is not limited to 
linear operators and can in fact realize very varied operators. For 
example, it is possible to realize an operator having a threshold effect 
by placing a group of thin films forming a diode in processing means 6. 
These non-linear operators are in practice used less than the linear 
operators. 
The realisation of a processing means including a non-linear operator is 
from the formal standpoint identical to realizing a processing means 
including a linear operator. The difference is based on the fact that the 
resistive layer is replaced or completed by one or more layers of 
different types. These modifications fall within the routine activity of 
the expert. Therefore, a description will only be provided of two 
embodiments of the device according to the invention in which the 
processing means includes a linear operator or a non-linear operator, 
which can be expressed with the aid of two linear operators. 
In general terms, and this is the case of the operators used in the devices 
described hereinafter, the operator simultaneously has positives 
coefficients and negatives coefficients. However, the resistive layer of 
the processing means 6 only makes it possible to express the absolute 
value of these coefficients. In order to be able to realize the operator, 
it is therefore necessary for the input means 4 to supply at each 
elementary input point 10, the voltage signal associated with said 
elementary input point and the opposite voltage signal. In practice, each 
elementary input point 10 can be constituted by a plurality of separated 
conductive elements. 
A description will now be given of a local image processing device 
according to the invention leading to an increase in the contrast of the 
image received, so as to permit a better detection of contours. This 
Laplacian-type operator is shown in the following table 1 with a 3.times.3 
processing window. 
TABLE 1 
______________________________________ 
-1 -1 -1 
-1 8 -1 
-1 -1 -1 
______________________________________ 
This operator makes it possible to supply at each elementary output point 
of the processing means a voltage signal equal to eight times the voltage 
signal of the corresponding elementary input point reduced by the sum of 
the voltage signals of the elementary points adjacent to said elementary 
input point. 
FIG. 2 is an exploded view of the input means and the processing means of a 
processing device according to the invention implementing said operator. 
It will be described in conjunction with FIG. 3 showing a section along A 
of plane P of FIG. 2. The input means shown therein is of the solid camera 
type and permits the conversion of a light image into a group of parallel 
electrical signals arranged in matrix-like manner. 
This input means comprise a group of thin films deposited and etched on a 
transparent substrate 14. Each of these films has a thickness of 
approximately 100 nanometers. The input means comprises three films or 
layers: 
a transparent conductive film 16 in which are etched two interdigitated 
transducers 16A, 16B providing two opposite voltages at each elementary 
input point, 
a conductive film 18 for converting the light intensity received by an 
elementary input point into an electrical signal, 
an electrically insulating film 20 in which are made two holes 22A, 22B for 
each elementary point and respectively positioned facing conductor 16A and 
conductor 16B. 
The light image processed by the processing device is received through the 
transparent substrate 14. It passes through the conductive film 16 made 
e.g. from indium oxide or tin oxide, which is transparent to light rays if 
the thickness of the film is not excessive. This light signal received by 
an elementary point is converted into two electrical signals of opposite 
signs by the photoconductive film 18, e.g. made from amorphous 
hydrogenated silicon. The amplitude of these electrical signals is a 
function of the light intensity received by the elementary point. 
The photoconductive film 18 is covered with an insulating film, e.g. of 
SiO.sub.2 in which are formed two holes 22A, 22B for each elementary 
point. The bases of these holes constitute the conductive elements of the 
elementary input point and ensure the connection between the input means 
and the processing means. 
In the embodiment of FIG. 2, this processing means comprises: 
a first conductive film in which is etched a group of parallel conductive 
lines 24, 
a resistive film 26, 
an insulating film 28, 
a second conductive film in which is etched a second group of parallel 
conductive lines 32, each of said lines being, connected to the resistive 
film by a plurality of contact holes made in the insulating film 28, 
an insulating film 34. 
a third conductive film in which are etched the elementary output points, 
38, each connected to a conductive line 32 by a hole 36 in insulating film 
34. 
These different films can be produced in accordance with any known process 
and from any known material. The conductive films can in particular be of 
A1, the insulating films of SiO.sub.2 and the resistive film doped Si-H. 
The first conductive film is etched so as to produce a group of parallel 
conductive lines 24, each line having a length which is substantially 
equal to the size of the processing window and is centred on a contact 
hole 22A, 22B of insulating film 20. 
Film 22 is successively covered with a resistive film 26 and an insulating 
film 28 in which are made holes 30A, 30B. These holes are positioned in 
reletion with the conductive lines of film 24. 
The electrical voltage taken in each hole 30A, 30B is consequently a 
function of three factors, namely the resistivity of film 26, the voltage 
present on the conductive line of film 24 facing said hole and finally the 
surface of the hole. As film 26 has a homogeneous resistivity, the 
resistivity differences to the right of each hole 30A, 30B are essentially 
a function of the surface of said hole. 
This makes it possible to obtain the different coefficients of the 
processing operator. Thus, in the case of a conductive line 32 etched in 
the second conductive film deposited on the insulating film 28, said line 
32 is positioned so that it is connected, via holes 30A, 30B, to the 
conductive lines etched in film 24. More specifically, said conductive 
line 32 is connected to nine conductive lines of film 24 (for a 3.times.3 
window), said conductive lines supplying voltage signals, whose sign 
corresponds to the sign of the processing operator coefficient. 
In the particular case of the Laplacien operator considered, the central 
coefficient of the operator is eight times greater than the other 
coefficients. In order that this coefficient difference appears during 
summation on conductive line 32 of the signals supplied by conductive 
lines 24, it is necessary for the contact hole 30B connecting the 
conductive line 32 associated with an elementary point and the conductive 
line etched in film 24 associated with the same elementary point to have a 
larger surface than the other contact holes 30A connecting said conductive 
line 32 to the conductive lines 24 corresponding to the neighbours to said 
elementary point. 
For each elementary point, the signal resulting from the application of the 
processing operator to said elementary point and to its neighbours is 
consequently obtained by conductive line 32. These conductive lines 32 
form a group of parallel lines substantially perpendicular to the group of 
parallel conductive lines etched in film 24. 
Finally the processing means is provided with an insulating film 34 in 
which there is a contact hole 36 for each elementary point. This 
insulating film is covered by a conductive film in which are etched 
elementary output points 38, which are in contact with a conductive line 
32 via contact holes 36. 
With reference to FIGS. 2 and 3 a processing device according to the 
invention has been described which uses a conventional mathematical 
operator. It has been shown that the realization of the device according 
to the invention leads to no particular difficulties, the technology of 
thin films having been mastered in numerous technologies and only a small 
number of films is required for producing the processing means. 
It should be noted that the output means of the processing device has not 
been shown in FIGS. 2 and 3. Preferred embodiments of the output means 
have been referred to hereinbefore, namely an addressing matrix making it 
possible to supply a multiplex electrical signal and a liquid crystal 
display permitting a direct display of the bidimensional signal after 
treatment. 
As the practical realization of the different output means is well known in 
fields close to those of the invention, there is no need to go into 
further detail regarding the different embodiments of the output means 
which fall within the routine scope of the expert. However, it has been 
considered worthwhile to describe the input means because, although solid 
cameras are known and are based on an identical principle to that of the 
input means described, said input means has arrangements for the purpose 
of supplying two opposite voltage signals at each elementary point. 
The processing device described hereinbefore essentially has four films, 
two conductive line films 24, 32, a resistive film 26 and a 
photoconductive film 18. It is possible to simplify the device by 
realizing the input means and the processing means with the aid of only 
two main films, namely a photoconductive and resistive film and a 
conductive line film. A processing device according to the invention based 
on this simplified embodiment will now be described relative to FIGS. 4A, 
4B and 4C. 
This simplified embodiment can be used for representing numerous 
mathematical operators and particularly the Laplacien operator described 
relative to FIGS. 2 and 3. To illustrate this second embodiment, a 
description will be given of a processing device implementing a non-linear 
operator, namely the SOBEL operator. It can be looked upon as a vector 
operator having two components, each formed from a linear operator. 
This operator has 18 coefficients (for a 3.times.3 window) among which 6 
coefficients are zero. The number of non-zero coefficients to be replaced 
by connections in the processing means remains high. Therefore the 
realization of the processing means is far from easy, particularly in the 
embodiment only having one photoconductive and resistive film and one 
conductive line film. 
This operator can be simplified to retain a smaller number of coefficients. 
A description will be given of an embodiment of the device according to 
the invention using a truncated SOBEL operator with only 8 non-zero 
coefficients. It has been experimentally found that for any applications, 
this operator supplies results very close to those of the SOBEL operator. 
The components of the truncated SOBEL operator are shown in the following 
table 2. 
TABLE 2 
______________________________________ 
1 2 0 0 0 -1 
G.sub.x = 
0 0 0 G.sub.y = 
2 0 -2 
0 -2 -1 1 0 0 
______________________________________ 
The truncated SOBEL operator consists of applying the component operator 
G.sub.x to each group of 9 elementary input points (for a 3.times.3 
window) for supplying a first component of an output signal and then the 
component operator G.sub.y for supplying a second component of an output 
signal, the signal supplied by the elementary output point being equal to 
the modulus of said output signs). This modulus can be particularly easily 
obtained in the case where the signals received by the processing means 
are a.c. signals. Thus, in this case, the modulus of the output signal is 
simply equal to the sum of its components if the latter are in quadrature. 
As the truncated SOBEL operator is formed from two linear operators, each 
elementary input point has four conductive elements, two conductive 
elements being associated with the operator G.sub.x and supplying signals 
of opposite voltage whose intensity is a function of the bidimensional 
signal received and two other conductive elements associated with the 
operator G.sub.y and supplying signals of opposite voltage which are also 
a function of the bidimensional signal received. 
In the special case which is of interest in practice, where these voltage 
signals are a.c. signals, the two conductive elements associated with the 
operator G.sub.x receive two opposite a.c. signals and the two conductive 
elements associated with the operator G.sub.y receive two other opposite 
a.c. signals, said signals associated with the operator G.sub.x and said 
other signals associated with the operator G.sub.y being in quadrature. 
FIG. 4A shows in exemplified manner an input means for carrying out an 
optoelectrical conversion of a bidimensional optical signal supplying, for 
each elementary point, 4 a.c. voltages in the manner indicated 
hereinbefore. 
This input means comprises a group of 4 electrical conductors 44A, 44B, 
44C, 44D etched in a conductive film deposited on a transparent substrate 
42. These conductors have a geometry and are interleaved in such a way 
that a fraction of each of them is located above each elementary point 40. 
These fractions constitute the conductive elements 46A, 46B, 46C and 46D 
associated with the elementary point 40. 
The conductive elements defined here are not identical to the conductive 
elements 24 defined with reference to FIGS. 1 to 3, because they carry a 
fixed modulus supply voltage and not a voltage which is a function of the 
bidimensional signal received. It is not possible here to define an 
elementary input point in the sense of FIGS. 1 to 3, i.e. a group of 
conductive elements electrically connecting the input means to the 
processing means. 
The conductive elements 46A and 46D receive opposite a.c. voltage signals. 
In the same way, the conductive elements 46B and 46C receive opposite a.c. 
voltage signals, said signals being in quadrature with the signals 
received by the conductive elements 46A and 46D. 
A photoconductive, resistive film 48 is deposited on the electrical 
conductors. This film can be of an appropriately doped 31-H and is itself 
covered with an electrically insulating film 50 having a plurality of 
holes 52, 54, as shown in FIG. 4B. As stated hereinbefore, the voltage at 
the base of each hole reflects the light intensity of the optical signal 
received by the elementary input point having a coefficient linked with 
the size of said hole and having a sign (a phase for an a.c. signal) 
linked with the input conductor SCOVO which said hole is located. 
For the truncated SOBEL operator, the non-zero coefficients are in absolute 
values equal to 1 or 2. In the processing means, said coefficients are 
respectively translated by holes 52 and 54, holes 52 being smaller than 
holes 54. 
These holes make it possible to bring about an electrical contact between 
on the one hand the photoconductive, resistive film 48 and on the other 
the conductive elements 56 etched in a conductive film 58 deposited on the 
insulating film 50. Each conductive element 56 simultaneously receives the 
four signals corresponding to the four coefficients of component G.sub.x 
of the truncated SOBEL operator and the 4 signals corresponding to the 4 
coefficients of component G.sub.y of the truncated SOBEL operator. 
The voltage present on each conductive element 56 is consequently equal to 
the modulus of the signal, whose components are output signals 
respectively corresponding to operators G.sub.x and G.sub.y. Thus, this 
voltage is the output voltage of the elementary point. 
As shown in FIG. 4C, this conductive film 58 is covered with an insulating 
film 60 in which are made contact holes 62, each corresponding to an 
elementary point. This insulating film 60 is itself covered with a 
conductive film 64 in which are etched the elementary output points 66. 
The electrical image formed by the group of voltage signals supplied by the 
elementary output points can be exploited in any known manner. 
Advantageously it is possible to cover the conductive film 62 with a 
liquid crystal film and then by a transparent electrode connected to 
ground. The output means constituted by these two latter films then forms 
a liquid crystal display making it possible to directly display the 
processed image. According to another advantageous embodiment, the output 
means can be constituted by an addressing matrix for transmitting the 
processed image in the form of a frame of a video signal.