GB2224351A - Camera for optically processing 2-D image information by means of optical characteristics that involve image analysis - Google Patents

Description

1

DESCRIPTION A CAMERA FOR OPTICALLY PROCESSING TWO-DIMENSIONAL IMAGE INFORMATION BY MEANS OF OPTICAL CHARACTERISTICS THAT INVOLVE IMAGE ANALYSIS

The present invention relates to a camera for optically processing twodimensional image information by means of optical characteristics that involve image analysis. It has applications in the fields of biology, medicine, environmental protection and related fields in the evaluation of biological and medical preparations, embodied as a microscope camera attachment, for example. Furthermore, it has uses in industrial robot technology in the form of an optical sensor which can differentiate between components and other elements, and also in the building and construction industry for the rapid optical surveying of buildings. Another field of application may be found in safety control systems.

Electromagnetic radiation is known to include characteristic information concerning factors such as the quantity, the phase, wavelength and the direction of polarisation, all of which can be used to distinguish different object images. With these characteristics, various methods of optical image processing are possible, the methods being specified according to that feature of the electromagnetic waves which is utilised as an information carrier:

optical Fourier analysis multispectral analysis polarisation-dependent analysis.

The optical Fourier analysis of images can be performed in both a coherent manner (relevant examples are cited by PERNICK et al in Applied Optics 17(l) 1978,21 and KRUGER et al in Applied Optics 16(10) 1977, 2637) and, as well, in an incoherent manner (relevant examples are published by CARTWRIGHT et al in Proceedings of SPIE, Vol. 422, N. Y. 1982 and in the DD-patent specification 246 466).

In contrast to optical Fourier analysis, multispectral technology does not use the local distribution of the value and phase of the electromagnetic wave as an information carrier, but the spectral composition of the latter.

After light is dispersed into various spectral ranges by means of a multispectral camera (for example an MKF 6 - or MSK 4 - camera of the Kombinat VEB Carl Zeiss JENA) evaluation of the image content is carried out on the basis of the spectral components included in the individual image parts, by means of a multispectral projector (e.g. the MSP 4C projector of the same manufacturer), or with a special electronic data processing system. The disadvantage of this method consists mainly in the fact that the -3image recording and evaluation processes do not coincide and the evaluation process requires a relatively considerable effort. In addition, image information may be included exclusively or additionally in the local distribution of the direction of polarisation of the electromagnetic wave. One typical example of this does exist in polarised microscopy where the sample to be examined is illuminated with linearly polarised light, the direction of polarisation being changed locally according to the matter distribution of the sample to be examined. The electromagnetic wave is then investigated and evaluated at the image-side by an analyser (polarising filter) - (see for example BEYER: Handbuch der Mikroskopie, Verlag Technik, Berlin). With methods used in prior art, is is usual to process image information being used for object classification exclusively either by analysis of local spectrum regions, multispectral analysis, or by polarisation-dependent image analysis. A first attempt at coupling the processing methods of optical Fourier analysis and multispectral analysis is described by ZIMAN ("0 strukturzonalnej Metodike" in "Isledowanie Zemlie iz Kosmosa" (1980)4). In this particular case, the zone-sampled parameters of the Fourier analysis being utilized for the -4classification, are supplemented by a number of multispectral parameters which are each a representation of one averaged intensity value of the image segment sampled entirely in one spectral region sampling location. This means, therefore, that inclusion of additional parameters and an increase in the number of measured values to be electronically evaluated, the latter of which are independent of one another, consequently increases the material and temporal evaluation effort.

It is an object of the present invention to provide a camera for optically processing two-dimensional image information by means of optical characteristics in conjunction with image analysis which does not require any additional effort for electronically processing the measured values in order to increase the classification probability. Thus, it is a feasible method for rapid optical image processing with which reliable statements about the objects, investigated with simple means, can be obtained and in real-time.

In accordance with the present invention a camera for processing twodimensional image information by means of optical characteristics that involve image analysis comprises an imaging optical train, further comprising a camera lens and an image recording medium positioned in the image plane of the camera lens, an evaluating optical train further comprising in successive arrangement, a radiating source, a diaphragm arrangement that is switchable into any mask form and position, an optically refractive system including the image recording medium of the imaging optical train and an opto-electronic receiver; said evaluating optical train being redirected away from the imaging optical train by means of a semitransmitting mirror (beam -splitter), and the diaphragm arrangement, being imaged, sharply defined, into a receiver plane via the optically refractive system and an evaluation unit for zone- sampled values which is coupled to a receiver; wherein the switchable diaphragm arrangement is a liquid crystal display, the image recording medium is an optical image converter, an optical filter arrangement is positioned in front of the image converter within the imaging optical train and whereby a driving unit is arranged for arbitrary driving of the diaphragm arrangement and of the filter arrangement as well as for transmitting the information of the chosen diaphragm-filter combination to the evaluation unit for zone-sampled values.

i Preferably, a liquid crystal (LC) display including a polariser in front of it and an analyser following it, is applied as a diaphragm arrangement to implement any suitable mask form and mask position. The image converter is preferably an LC-image converter readable by means of reflection.

Preferably, the switchable filter arrangement may consist of a colour filter unit and/or a linear rotatable polariser. Hence, the colour filter unit can be realised in different ways.

Preferably, the colour filter unit consists of nematic liquid crystals that generate interference patterns, said colour filter unit being positioned between crossed polarisers so that different interference colours arise due to variations in the driving voltage.

In one embodiment, the colour filter unit comprises two twist-cells and two phase-retarding plates followed by a polariser. Thus, the combination of a number of single switching states will provide four fundamental wavelengths.

In a preferred embodiment, the colour filter unit comprises nematic LClayers having inserted between them different dyes which are switchable regarding their transmission, by means of the "guest-hostef fect".

Preferably, the linear rotatable polariser can comprise a linear polariser and a 90'-twist-cell.

The operational mode of such a camera according to the invention is one wherein the cycle of the driving means of the unstructured switchable colour unit and/or the rotatable polarisers is altered, and during image capture/recording, driving means of the optical filter unit is by means of the known method of incoherent zone-structure analysis, and zone integral measurement values can then be determined from corresponding variations in the diaphragm arrangemen which produces mask forms and mask positions.

With 'k' different positions of the colour filters, 't' different positions of the polarising filters and 'm' various mask forms and/or mask positions of the diaphargm position, and by means of a control unit, successively different combinations of these factors will result in N - k. e.m. (a maximum number) different multi-character measured values, if all possibilites of this arrangement are exhausted.

In this case the diaphragm arrangement is used to generate different mask forms and mask positions, radiating surfaces then representing integral zones as they do in incoherent zone-structural-analysis. It has to be guaranteed, however, that the radiating zones will emit polychromatic and/or radiating zones and linearly-polarised polychromatic light, respectively. To achieve sufficient incoherence of the radiation., a diffusing screen may i -8be disposed between the usual thermal radiating source and the diaphragm arrangement.

The image recording medium applied which is suitable as a rapid LC-image converter in a simultaneously performed evaluation process, is important for fulfilling all the tasks of.a real-time image processing camera.

As is usual essential factor consists in the learning process comparison values process does not efforts despite in zone-sampling analysis, an of the functional mode of the camera so- called programming process or for generating the required within the evaluating unit, which demand any additional programming adding several other characteristic features of the radiation. Accordingly, the wavelength and/or the polarisation state of the examined objects are directly integrated into the zone-sampling evaluation process and will increase the reliability of the information on the objects.

In addition., it should be mentioned that the basic principle of the invention can also be implemented by applying image recording media which do require an intermediate processing procedure when the imaging optical train is separated from the evaluating optical train, provided real-time image processing is not -9required. For multiple characteristics that involve image analysis it is also feasible to evaluate such object images which have not been dispersed multispectrally, or, by means of polarisationdependent image analysis in the evaluating optical train according to the invention, by inserting in addition, coloured and/or polarised filters advantageously near to the receiver.

Employing simple means only, with the camera according to the invention, an arrangement operating in real-time has been developed, which permits multiple characteristics involving image processing on the basis of zonesampling, multispectral and polarisation-dependent optical analysis without increasing the effort of electronically evaluating measured values. The attainable classification probabilities can be increased, or the evaluation time can be decreased with fewer measured values.

The present invention is further described hereinafter. by way of example only, with reference to the accompanying drawings, in which:

Fig.1 illustrates a camera for optically processing two-dimensional information by means of multiple characteristics that involve image analysis according to the present invention, in its basic set-up; Fig.2 shows the construction of the colour filter unit, and Fig.3 is an embodiment of the image processing.

The arrangement shown in Fig.1 comprises an imaging optical train with a camera lens 1, an optical filter arrangement 2 and an image converter 3; further comprising an evaluating optical train that includes a thermal radiation source 4, a diaphragm arrangement 5, an optically refractive system 6, an image converter 3 and an opto-electronic receiver 7.

The imaging and evaluating optical trains are arranged on a common optical axis 9. The receiver 7 is coupled to a common optical axis 9 via a semi-transmitting mirror (beam-splitter) 8. The diaphragm arrangement 5 comprises a liquid crystal cell 51 and crossed polarisers 52 and 53, the liquid crystal cell 51 being disposed between the crossed polarisers.

In this arrangement, the image converter 3 is readable by means of reflection, based on the LC-principle, for example. In carrying out zonesampling analysis, image converters 3 will usually generate only images for evaluation on the read-out side which only include information concerning the local intensity distribution being exposed at the write-in side by the camera lens 1 onto the image converter 3. But this way, the image information contained in the local spectral and polarisation distribution of the object scene can not 1 1 -11be detected. Therefore, the filter arrangement 2 is positioned in front of the image converter 3 and used to convert the spectral and polarisation features of the radiation into intensity distributions.

The filter arrangement 2 may comprise a colour filter unit 21 and/or a rotatable polariser. This particular embodiment has both combined. The colour filter unit can be put into operation in various ways. One feasible means enlists the use of a magazine-shaped and mechanically switchable arrangement of different fixed filters. Considering only the mass, it is more favourable for portable cameras to utilise media that operate with electro-optical effects. The colour-selecting filters may be nematic, interference-pattern-generating LC-layers which are positioned between crossed polarisers, different interference colours being generated by a variation in the driving voltage.

A second way of implementing the colour filter unit is with an arrangement of two twist-cells and two phase-retarding plates which are each disposed between the twist-cells and with the polarisers following. By combining the individual switching states-, four fundamental wavelengths having a width of approximately 100 nm can be set.

The most advantageous variant of switchable colour filters is based on the guest-host-effect where the application of nematic, liquid crystals and dyes inserted, causes a change in the absorption of light when the voltage is changed.

Fig.2 shows the arrangement of the entire colour filter unit 2. As in known methods of orientation, a planar orienation of the nematic. dyedoped LC-layer 123 is achieved with its disposition between glass substrates 122.. and with further coatings of transparent electrodes 121 to form an LC cell. An arrangement consisting of three such cells each containing a different dye, upon irradiation with linearly polarised light passing through the polariser 124, enables different colours to be selected in different driving states. This form of colour selection can for example, be performed for the colours blue, yellow and red.

For analysis of polarisation state using the rotatable linear polariser 22, it is advantageous to use a 90'-twist-cell in co-operation with a linear polariser.

In the twist-cell a rotation of the direction of polarisation by 90' occurs, provided the direction of polarisation coincides with one of the axes of the LC-director. When a voltage is applied to the liquid k -13crystal, the twisting states of the LC-molecules and therefore the torsion of the direction of polarisation, are cancelled. The x-component can then be evaluated in the electrically "dead" state and the ycomponent in the driven state.

Additional elements shown in Fig.1 that improve the evaluation process, are the diffusing screen 41 which has to be assigned to the radiating source 4 to ensure sufficient incoherence of the light emitted by the latter. and a diaphragm 7 which is arranged as a pinhole-diaphragm on the angled optical axis, directly in front of the receiver 7.

The colour filter unit 21 and the rotatable linear polariser 22 receive their driving signals from a driving unit 11 which is connected to the evaluation unit 12 via synchronous and revertive signals. Additionally, the diaphragm arrangement 5 is driven by the driving unit 11 so that with each fixed filter combination of the colour filter unit 21 and the rotatable linear polariser 22, different mask forms and mask positions can be achieved, and result in one multiple characteristic involving the measured value at the output of the opto-electronic receiver 7 in each case. With this series of measured values the evaluation unit 12 will carry out exactly the same mathematical operations as they are required for the -14zone-sampling analysis. Accordingly, the programming and evaluating effort, in principle, remains the same as it would be in exclusive zone- sampling analysis. For clarification purpose, Fig.3 represents a less sophisticated variant of the image processing according to the basic principle of the invention. In this case it is assumed that an object scene 10 (Fig.1) was recorded on an image recording medium 33 during an imaging process which is now complete, the colour and the polarisation distribution of the object scene 10 being included. In this case, the arrangement can be simplified and the filter arrangement 2 comprising a colour filter unit 21 and a rotatable linear polariser 22 has to be inserted into the evaluating optical train, the necessity to angle the adjoining optical axis according to Fig.1 no longer existing (or only in the exceptional case of a non-transparent image recording medium 33). Advantageously, the filter arrangement 2, which is set up and driven in the same way as described in the first example, is positioned near the receiver 7. The driving, synchronisation and evaluation of the multiple characterstics involving measured values, is carried out in a manner similar to that described in the first embodiment.

i k J 1

Claims (11)

_15CLAIMS

1. A camera for processing two-dimensional image information by means of optical characteristics, comprising an imaging optical train, which includes a camera lens and an image recording medium positioned in the image plane of the camera lens, an evaluating optical train which includes in successive arrangement, a radiating source, a diaphragm arrangement that is switchable into any mask form and position, an optically refractive system including the image recording medium of the imaging optical train and an opto-electronic receiver; said evaluating optical train being redirected away from the imaging optical train by means of a semi-transmitting mirror (beam-splitter), and the diaphragm arrangement being imaged, sharply defined, into the receiver plane via the optically refractive system and an evaluation unit for zone-sampled values which is coupled to the receiver; wherein the switchable diaphragm arrangement is a liquid crystal display, the image recording medium is an optical image converter, an optical filter arrangement is positioned in front of the image converter within the imaging optical train and wherein a driving unit is arranged for arbitrary driving of the diaphragm arrangement and of the filter arrangement as well as for transmitting the -16information of the chosen diaphragm-filter combination to the evaluation unit for zone-sampled values.

2. An arrangement as claimed in claim 1, wherein the diaphragm arrangement is a liquid crystal display (LCD) having a polariser in front of it and an analyser following it.

3. An arrangement as claimed in claim 1, wherein the image converter is an LC-image converter that is readable by means of reflection.

4. An arrangement as claimed in claim 1, wherein the switchable optical filter arrangement is a colour filter unit having different, arbitrarily switchable colour filters.

5. An arrangement as claimed in claim 4, wherein the colour filter unit consists of nematic liquid crystal layers having different dyes inserted and being switchable regarding its transmission by means of a guest-hosteffect.

6. An arrangement as claimed in claim 4, wherein the colour filter unit comprises nematic liquid crystals that generate interference patterns, and being disposed between crossed polarisers.

7. An arrangement as claimed in claim 4, wherein the colour filter unit consists of two twist-cells and two phase-retarding plates located between said twist-cells with a polariser adjacently disposed.

-1 9 I 1

8. An arrangement as claimed in claim 1, wherein the switchable optical filter arrangement is a rotatable linear polariser.

9. An arrangement as claimed in claim 8, wherein the rotatable linear polariser comprises a 90'-twist cell and a fixed linear polariser.

10. An arrangement as claimed in claim 1, wherein the switchable optical filter arrangement comprises a colour filter unit and a rotatable linear polariser.

11. A camera for optically processing twodimensional information by means of various optical characteristics substantially as hereinbefore described with referece to and as illustrated in the accompanying drawings.

Published 1990atThePatentOffice, State HouBe,68/71 High Holborn, London WCIR4TP.Purther copies maybe obtained from The P&tent0frlce. Sales Branch. St Mary Cray, Orpington, Kent BR5 3RD. Printed bY Multiplex techniques ltd, at Mary Cray, Kent. Con 1/87

11. A camera for optically processing twodimensional information by means of optical characteristics that involve image analysis, substantially as hereinbefore described with referece to and as illustrated in the accompanying drawings.

0 Amendments to the claims have been filed as follows 1. A camera for processing two-dimensional image information by means of various optical characteristics, comprising an imaging optical train, which includes a camera lens and an image recording medium positioned in the image plane of the camera lens, an evaluating optical train which includes in successive arrangement, a radiating source, a diaphragm arrangement that is switchable into any mask form and position, an optically refractive system including the image recording medium of the imaging optical train and an opto-electronic receiver; said evaluating optical train being redirected away from the waging optical train by means of a semitransmUting mirror (beam-splitter), and the diaphragm arrangement being imaged, sharply defined, into the receiver plane via the optically refractive system and an evaluation unit for zone-sampled values which is coupled to the receiver; wherein the switchable diaphragm arrangement is a liquid crystal display, the image recording medium is an optical image converter, an optical filter arrangement is positioned in front of the image converter within the imaging optical train and wherein a driving unit is arranged for arbitrary driving of the diaphragm arrangement and of the filter arrangement as well as for transmitting the i 7 lq 8. An arrangement as claimed in claim 1, wherein the switchable optical filter arrangement is a rotatable linear polariser.

9. An arrangement as claimed in claim 8, wherein the rotatable linear polariser comprises a 90'-twist cell and a fixed linear polariser.

10. An arrangement as claimed in claim 1, wherein the switchable optical filter arrangement comprises a colour filter unit and a rotatable linear polariser.