GB2149257A

GB2149257A - Optical pattern recognition apparatus

Info

Publication number: GB2149257A
Application number: GB08425374A
Authority: GB
Inventors: Leslie Charles Laycock
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1983-10-17
Filing date: 1984-10-08
Publication date: 1985-06-05
Also published as: GB2149257B; GB8425374D0

Abstract

In an optical pattern recognition apparatus, an image representing a scan (which may be optical, IR or radar) of a scene is projected B1 onto a bismuth silicon oxide crystal 5. A second image representing a reference image 9 is projected B2 onto the crystal as well, and a hologram-type interference pattern, in the form of a third image representative of the correlation product of the first (input) image and the second (reference) image. A light sensitive detector array 21 is provided, together with means 3, 19 for projecting the third image onto the array 21, which provides an output signal representative of the position of a correlation peak in the correlation product image, and hence representative of the position in the reference image of the part of the reference image which correlates with the input image to give rise to the correlation peak. <IMAGE>

Description

SPECIFICATION Optical pattern recognition apparatus This invention relates to optical pattern recognition apparatus.

More particularly the invention relates to optical pattern recognition apparatus of the kind in which an image representative of the correlation product of an input image and a reference image is generated.

According to the present invention in an apparatus of the kind specified there is provided a light sensitive position detector array and means for directing said image representative of said correlation product onto said array, thereby to provide an output signal representative of the position of a correlation peak in said correlation product image, and hence representative of the position in said reference image of the part of said reference image which correlates with the input image to give rise to said correlation peak.

Said output signal may simply be used to provide an indication of the position of the said part of the reference image in the reference image. However in a preferred embodiment of the invention means are provided to use said output signal to vary the reference image so that said part of the reference image is at a predetermined position on the reference image.

In one such preferred embodiment the input image is a portion of a scene, said reference image is representative of a portion of a map of said scene, and means are provided for using said output signal to vary the portion of the map which the reference image represents as the input scene changes so that the reference image tracks the input image.

An apparatus in accordance with the invention, will now be described by way of example only with reference to the accompanying drawing which is a schematic diagram of the apparatus.

Referring to the figure, the apparatus is located in a moving vehicle (not shown) and includes a spatial light modulator 1 arranged to produce a coherent light beam B1 from a coherent light source (not shown) within the vehicle, spatially modulated with an image derived from input data fed into the modulator in the form of an incoherent optical, radar, or thermal image of the current scene outside the vehicle. The beam B1 is arranged to pass through a Fourier transform lens 3 positioned to produce the Fourier transform of the beam B1 in a single crystal of bismuth silicon oxide 5. The apparatus also includes a map scanning/beam deflector system indicated as 7 including a reference map 9 in the form of a slide containing data relating to a large area of the outside world over which the vehicle is moving.The coherent light source is arranged to produce a second beam of light B2 which passes through a portion of the map 7 such that the beam is spatially modulated with the pattern on that portion of the map. The system 7 includes a beam deflector 8 arranged to deflect the beam B2 so that it passes through a scale and orientation dither system 11, and then through a Fourier transform lens 1 3 positioned to produce the Fourier transform of the pattern in the beam B2 in the crystal 5. A display 1 5 connected to the system 7 is arranged to display the X and Y co-ordinates of the portion of the map through which the beam B2 passes. The coherent light source is arranged to produce a third beam B3 propagating in the opposite direction to the beam B2, such that the beams BI, B2 and B3 converge in the crystal 5.A beam splitter 1 9 is placed in the beam path between the spatial light modulator 1 and the lens 3 as shown, with an array 21 of photoelectric detector elements positioned at the side of the beam path. X and Y co-ordinate outputs of the array 21 are connected to the system 7.

As the counter propagating beams B2 and B3, and the beam B1 interact in the optically non-linear bismuth silicon oxide crystal 5 an effective grating structure is formed within the crystal by the beams B1 and B2. A further beam B4 is then produced with can be considered as the diffraction of the beam B3 from the induced grating, the beam B4 propagating in the opposite direction to the beam B1, this being the phenomenon known as degenerate four wave mixing. With the particular configuration of beams B1, B2, B3 in which the beam B1 contains the Fourier transformed inpur scene image, and B2 the Fourier transformed pattern on the illuminated portion of the map 7, the beam B4 will contain the product of the two Fourier transforms.As the beam B4 emerges from the crystal 5 it will pass through the lens 3, which will perform an inverse Fourier transform of the beam, such that the beam B4 is spatially modulated with the correlation product of the image in the beam B1 and the pattern on the portion of the map. The beam B4 will then be deflected by the beam splitter 19, such that it is incident on the array 21.

In use of the apparatus the beam B2 is scanned across the map 7 until a correlation peak is detected on the array 21, the scale and orientation dither system 11 altering the scale and orientation of the pattern in the beam to aid this process. When such a peak is detected electrical signals representative of the X and Y co-ordinates of the peak are fed from the array to the scanning/deflector system 7. The map 9 is then moved in response to these signals relative to the beam B2 such that a slightly different portion of the map is illuminated and the correlation peak appears in the centre of the array 21. The illuminated portion of the map 9 is thus centred on the instantaneous input scene represented by the data fed into the spatial light modulator 1.As the input scene changes as the vehicle moves over the area represented on the map, the apparatus will then automatically track the input scene on the map as it varies, the current location of the illuminated portion of the map being displayed on the display 1 5. A system for producing a dither on the position of the correlation peak, for example by dithering the position of the reference map 9 relative to the beam B2, may be incorporated in the system 7, this increasing the accuracy of the centring mechanism by the possibility of using phase sensitive detection to determine the offset of the correlation peak on the array.

It will be appreciated that as the correlation peak is arranged by the feed-back mechanism to be at the centre of the beam B4, and the map is centred on the inut scene, off-axis aberrations of the lenses 3, 13, are avoided.

The apparatus also has particular application in a vehicle guidance system for use in guiding the vehicle to a desired location. The reference image will then be representative of the desired location, whilst the input image is representative of the actual location of the vehicle. The output signal from the light sensitive position detector array may then be used by the guidance system to modify the actual location of the vehicle, to guide it towards the desired location.

It will also be appreciated that the apparatus has a wide range of other applications such as the monitoring of production processes.

Claims

1. An optical pattern recognition apparatus of the kind in which an image representative of the correlation product of an in-put image and a reference image is generated wherein there is provided a light sensitive position detector array and means for directing said image representative of said correlation product onto said array, thereby to provide an output signal representative of the position of a correlation peak in said correlation product image and hence representative of the position in said reference image of the part of said reference image which correlates with the input image to give rise to said correlation peak.

2. An optical pattern recognition apparatus according to either one of the preceding claims including control means for using said output signal to vary the reference image so that said part of the reference image is at a predetermined position on the reference image.

3. An optical pattern recognition apparatus according to Claim 2 in which said predetermined position is at a central position on the reference image.

4. An optical pattern recognition apparatus according to either Claim 2 or Claim 3 in which said input image is a portion of a scene, said reference image is representative of a portion of a map of said scene, and said control means use said output signal to vary the portion of the map which the reference image represents as the input scene changes so that the reference image tracts the input image.

5. An optical pattern recognition apparatus according to Claim 1 for use in the guidance system of a vehicle, said guidance system including means for using said output signal to modify the location of the vehicle.

6. An optical pattern recognition apparatus according to any one of the preceding claims including means for altering the relative scales of said reference image and said input image.

7. An optical pattern recognition apparatus according to any one of the preceding claims including means for altering the relative orientation of said reference image and said input image.

8. An optical pattern recognition apparatus according to any one of the preceding claims including means for dithering the position of said correlation peak within said correlation product image.

9. An optical pattern recognition apparatus according to any one of the preceding claims in which the means for generating said correlation product image comprises means for directing two coherent light beams onto an optically non-linear material, each of said two beams being spatially modulated with a respective one of said input image and said reference image; and means for directing a third coherent light beam onto said material so as to use the phenomenon of degenerate four wave mixing in said material to produce a fourth beam spatially modulated with said correlation product image.

10. An optical pattern recognition apparatus substantially as hereinbefore described, with reference to the accompanying drawing.