AU595953B2

AU595953B2 - Video image analysis system

Info

Publication number: AU595953B2
Application number: AU81053/87A
Authority: AU
Inventors: Charles Thomas Austin
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-10-30
Filing date: 1987-10-28
Publication date: 1990-04-12
Anticipated expiration: 2007-10-28
Also published as: GB2197463A; AU4433089A; JPH01501114A; KR880702028A; WO1988003345A1; AU616573B2; AU8105387A; EP0292514A1; GB2197463B; GB8625957D0

Description

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PCT

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 88/ 03345 .H04N 5/235, G01B 11/28 Al (43) International Publication Date: 5 May 1988 (05.05.88) (21) International Application Number: PCT/GB87/00761 (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (Euro- (22) International Filing Date: 28 October 1987 (28.10.87) pean patent), FR (European patent), GB (European patent), IT (European patent), JP, KR, LU (European patent), NL (European patent), SE (European pa- (31) Priority Application Number: 8625957 tent), US.

(32) Priority Date: 30 October 1986 (30.10.86) Published (33) Priority Country: GB With international search report.

Before the expiration of the time limit for amending the claims and to be republished in the event of the receipt (71)(72) Applicant and Inventor: AUSTIN, Charles, Thomas of amendments.

[GB/GB]; The Old Rectory, West Lydford, Somerton, Somerset TA11 7DQ

AUSTRALIAN

(74) Agents: MUIR, Ian, Robertson et al.; Haseltine Lake Co., 28 Southampton Buildings, Chancery Lane, Lon- 2 5 MAY 1988 don WC2A IAT (GB).

PATENT

OFFICE

This document containg the amcndments made under Section 49 and is correct for plrinting. 19 ,O.JP. 2 3 Jt' 1988 (54)Title: -_MA IZrAtesS TTEST Ic- MACHtC E. i3C-OrL.poarttOG-- f k (MrC6-? fNArctL"fSS s-/s-T"r, n/ f 1 _r r^- (57) Abstract An image analysis system includes a means for forming an image of an object and an illumination apparatus, the illumination apparatus comprising: illumination means for illuminating the object; and processing means for comparing the brightness of the image with a predetermined brightness level or brightness levels, and capable of increasing or decreasing the light output of the illumination means on the basis of the result of said comparison. Also disclosed is a system including a measurement apparatus for comparing the size of an object with that of a reference object the apparatus comprising: a means for forming an image of the object whose size is to be determined, when the object is in a viewing position; and a reference object, mounted in the apparatus, which may be viewed, using the means for forming an image, instead of, or in addition to, the object whose size is to be measured. The invention is disclosed with particular reference to its incorporation in a static indentation hardness testing machine.

cables: Sandpat Melbourne This invention lelates to a hardness testing machine ifloorporating a system for analysis of an i-mage, suuh as one produced by a closed-circuit telpyision (OCTV) camern, Tn preferred embodiments, the invention iu applioable to a static indentation hardness testing machine, in which an image of an indentation is analysed using a COTV camera and a processor., In a static indentation hardnalss testing machine, the size of an indentation made in a metal object is used as a measure of the hardnoss or thftobjeot. It is important, therefore, that the size of the indentation~ be measured accurately.

1I .9 i well known that, in order to be able to analyso an image accurately, it is necessary for the object to have good illuminati~on, 1Yor many kinds of S object this Preponto no particular difficilty zind previously, in the field pf hurdness testing, It has been usual to measure the sizes of indentations using a microscope which uses a uingle level of illumination for different objects. In a prior proposal using a *CTV camera, described in EP-A-0048346, a constant illumination for different test objects of the same or 00 different type was uved. However, it has been determined that it ip difficult with constant illumination of metal objects, to analyse the image S with constant accuracy even when, in Bome cases, the 30 test objects aro different samples from the same, produtition run. It haa boon established that the variations of surface finish and refleativity can vary Signifonantly and produce Inaccuracies of analysis.

The present invention seeks to overcome these AU difficulties, by providing a machine in which the 1, amount of illumnination of an object may be varied, in -2order to achieve optimum illumination of the object.

An mentioned above, when using a static indentation hardness testing machine, there is a need to determine the size of an object (suoh ani an indentation in a Pample) Which. im viewed through a CC'2V camera, using an image processor. In such a machine, it has beea proposed to calibrate the processor by presenting to the COTY a referenoo object, which forms a calibration image, and which might take the form of a oalibrated 6coale, a representation of an object of the type under tnor an actual Pample of an object of the type under teat, the representation or the sample being of known size. If data concerning the tize of the reference object are input into the processor, which is 15 able to generate a measurement of the image size in units such as pixels or chord lengths, the sizes of objects subsequently placed inthe field of view of the .CCTV camera may be determined, These measurements may be made by comparloon between the size of the object in unitpsouch as pixelo or chord lengths compared with the known size of the calibration image in those unita.

Such a sYstem, however, has mnajor- practical disadvantages, In general, tho calibration image in placed by band, and needs to be positioned extremely accurately if subsequent measurements are to be made accurately, while the data ooncerning the size of tbo calibration image must be input manually into the processor, with the risk or error by the operator in addition, whenever re-calibration of the processor is carried Qut, the measurine operations of the machine must be Interrupted. As a result, there in a tendency to re-calibrate o~nlyinilfrequently. However, images produced by CCTV cameras may drift, or distort, with time or with variationa in temperature. 'Such changes may have a serious effect On the accuracy of a measurement system. This is particularly important _I-LLIIL- 3 2 3 4 6 7 8 9 i 0 12 13 14 16 17 S18 19 20 21 22 S* 0 0 23 24 26 27 y^N'28 because of the time taken to re-calibrate a processor, and hence the infrequency with which re-calibration is carried out.

The present invention seeks to overcome one or more of the disadvantages associated with known hardness testing machines.

According to the present invention, there is provided a static indentation hardness testing machine, for determining the hardness of a sample on the basis of the size of an indentation made in the sample, the machine including image analysis systeni which has a means for forming an image of an object, and an illumination apparatus comprising: illumination means, for illuminating the object; and processing means for comparing the brightness of the image with a predetermined brightness level or brightness levels, and capable of increasing or decreasing the light output of the illumination means on the basis of the result of said comparison.

Preferably, the means for forming an image of the object comprises a closed-circuit television system, although alternatively, an image array may be used. In a preferred embodiment, the illumination means is arranged to illuminate the surface of the sample surrounding the indentation, and the brightness of the image is determined from the brightness of the region outside the indentation.

Preferably also, the image analysis system comprises a processing means, for determining a grey level of the image at one or several locations in the image, and calculating a 891031,!psspe013,austin.res, 1. S4 mean grey level on the basis of said measured grey levels.

In the preferred embodiment, the calculated mean grey level is then compared with two predetermined grey levels forming the end points of a predetermined range. If the calculated mean grey level is outside the predetermined range, the light output of the illumination means is increased or decreased as appropriate.

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F1'7 891031,!psspeOl3,austin.res, _Vi9O thro'~ph he -amera,, a~ltl*' no a0 cbpo"4 4n' t am vjAw4na in44Thr For a better I understanding of the present invention, and to show how it may be carried into offoot, rerernce will now be made, by way of example, t~o tlhe accompanying drawingo in which:- F'iguare 1 is a block sohematic diagram showing an image illumination apparatus, forming part or an image analysis system in accordanoe wkth A fi-rot aspeot ot the present Invention; Figure 2 is a cross-section through a measurement apparatus, forming part of an imnage analysis system in accordance with eeeend 9cc~-f the invention; and Figure 3 is a view from below of the measurement 15 apparatus shown In Figure 2.

Figure 1 shows, schematically, an image illumination apparatus forming part of a hardness testing machine according to an embodiment If the firot ekspeat of the invention. A sample 1 is viewed through a television camera 2. In the preferrod embodiment of 0 9 5

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the invention, the sample bears an indentation, the size of whioh is tu be measured. The image from the camera 2 in transferred to a frame store 4 and then to a prooessor 3, in which the image is analysed. The processor ham access to the contents of an associated memory 20, and controls tho voltage supplied to a lamp 5 whIoh illuminates the object 1.

It has boon found that accurate analysis an image, and hence accurate measurement of the size of 30 the indentation in the sample, can bo consistently achieved if the mean grey level. at certain points In a fixed pattern which surrounds the atorod image of the hardness indentation lies within a particular range of grey levels. The fixed pattern is of importance because of the build up of material in the Immediate vicinity of a hardnemm Indentation, caused by tho .1 -6- *0 S 0

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If the level of illutmination is uncontrolled, the mean grey level found at the same points vill vary widely' depending upon the reflectivity of the sample in which the indentation io made. The reflectivity will depend upon the nature of the metal itself, and on the surface finish of the sample.

The Image viewed by the camera 2 is divided, by the frame store 4, into pixels, to each of whioh Is assigned grey level between 0 and 63. Appropriate programminig of the processor allows the size of the largest anticipated indentation to be identified, on the basis of known data about the hardness test. The processor then selects a number of pixels forming a 15 pattern approximately surrounding that notional indentation and calculates the mean grey level of these pixels. This ensures that the sampled pixels do not, in fact, form part of the Image of the actual indentation itself, but only of the surrounding material, As a result of a large number of such tests, it hau been possible to determine a range of such mean grey levels for which an accurate analysis of the image mny be achieved. Therefore, the calculated mean grey level in each case is compared with the end-points of 25 that range, which are stored in the memory 20. If the calculated mean grey level is below the desired range it is necessary to increase the illumination provided by the lamp 5, while if the calculated mean grey level In above the required range, it is neceoary to decrease :30 the level of illumination.

in an alternative embodiment, analysis of the imago may bo carried out in real time, if the processor 3 has sufficient memory 9apacity. In thin ease, it would not be necessary to provide the frame store as a separate device.

SThe lamp is of a conventional type, and is

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-7controlled by a lamp controller which is able to provide any one of 16 available discrete voltage outputs. Therefore, if it is required to increase the level of illumination, the voltage to the lamp is increased by one stop, while if it is required to decrease the level of illumination, the voltage to the lamp is decreased by one step. In order to obtain a mean groy level within the desired range, it may be necessary to repeat this operation, and to alter the voltage supplied to the lamp several times.

Figures 2 and 3 illustrate the apparatus used for mounting the sample and the reference object, in order to allow the reference object to be viewed without the *need for interrupting the measurement operations, and a 15 to substantially eliminate measurement errors caused by camera drift.

A camera extension tube 6 is mounted horizontally S" to the front of the camera 2 shown in Figure 1, and is mounted inside a support tube 7. At the end of the camera extension tube 6 is located a beam uplitting mirror 8, behind which is provided a front silvered mirror 9. Above the front silvered mirror is positioned a reference objooect 10, which is back-lit by a light uource mounted in a holder 11. The beam 25 splitting mirror is mounted in optical blocks 12, 13, which are connected to further optiaonl blocks 14, The optical blocks are provided with polarieers 16, 17, 1 and, adjacent the beam splitting mirror, there is provided an optical window 18, and, on the other side of the mirror, a diffuser 19.

Thin apparatus is intended to be used in connection with a hardness testing machine, and in particular a static indentation hardness testing maohlne for performing, for example, the Drinell hardnesa test. In this particular test, a measure of (l the hardnece of a material is formed by measuring the _J *i 4" 'A eizo of an indentation rormed in sample as a result of the applioation of' a known load. The mean diameter of the indentation formied by a spherical ball is iftvoraely proportional# for a given load, to the Brinell Hardness Number of the material. A sample, with ani indentation formed therein, in positioned below the optical wndow 18 along the axis B. An image of the indentaition is then reflected by the beam splitting mirror along axis A to the camera via the extension tube 61 which contains a lens to enlarge tho imago Pufficiently for measurement purposes.

The claims form part of the disclosure of this specification.

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a C jv\ANJ N 0 c~) *IYlilY~ LIr WO 88/03:345 PCT/GB87/0676 ,I The beam splitting mirror 8 is chosen such that approximately 50% of incident light is transmitted through the mirror and approximately 50% is reflected.

Thus, it is possible to illuminate the indentation from above the mirror, and this is done by positioning a light source, such as a fibre optic cable remotely supplied with light from the lamp 5, along the axis C.

As a result of the properties of the beam splitting mirror, it is also possible to view, through the camera, a second image. In this embodiment of the invention, an image of a back-lit reference object is reflected from the front silvered mirror 9, and partially transmitted through the beam splitting mirror 8 along the extension tube 6 to the camera 2. The reference object is an accurately made representation of a hardness indentation, surface etched onto polished opal glass. This object is mounted in the focal plane of the camera, and is visible to the camera only when it is back illuminated from a light source mounted in the holder 11 along the axis D.

As the reference object is fixed in position, it is illuminated only when it is required to re-calibrate the apparatus. Thus. the back illumination of the reference object is used only intermittently, while, for convenience, the lamp 5, illuminating the sample, is left on permanently. As it is required to view only one of the images at any time, it is necessary to prevent stray light from the light source along the axis C illuminating the reference object 10 via the ~mirrors 8,9. This is achieved by means of the cross polarised filters 16, 17.

When first used, it is necessary initially to calibrate the apparatus. The reference object is backlit, and no hardness indentation sample is present along axis B. Therefore, the only image visible is that of the reference object, which is of known size.

-9- Therefore, the image analysis system calibrates itself by means of the processor, by measuring the nuriber of pixels occupied by the calibration image, and determining a'relationship between the size of the object in millimetres and the measured number of pixels. Then, the light at D is switched off, and a metallic sample bearing a hardness indentation is moved into the focus of the camera along axis B. The camera now records the image of this hardness indentation, and, after making any necessary adjustments to the illumination of the sample, applies the relationship between pixels and millimetres derived from the calibration procedure to the size of the image, in pixels; thus, a measure of the size of the hardness indentation is achieved. Using this system, it is possible for the apparatus to be regularly recalibrated, since the time taken for the calibration is very short, and it may be carried out while one hardness indentation is being removed from the appratus and another is being introduced.

Thus, there is provided an image analysis system, which may be rapidly and accurately calibrated, in order to substantially eliminate the possibility of errors caused by camera drift or operator error. In addition, the invention provides a system which allows accurate analysis of the image to be made, by ensuring correct illumination of the object.

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Claims

2. A static indentation hardnass testing machine as claimed in claim 1, wherein the means for formi~ng an image of the object aomprises a closed-circuit *~.television system.
3. A static indentation hardness testing machine as claimod in claim 1, wherein the meana for forming an image of the object comprises an image array.
4. A static indentation hardness testing machine, as claimed in claim 11 2 or 3, wherein the processing means is adapted to determine the brightness of the 25 image from the brightness of the surface of the sample surrounding the indentation, A static indentation hardness testIng machine as claimed in any proceeding claim, wherein the proceasing meanm is adapted to determine a gro', lovel of the image at several locations in the image, and to calculate a mean grey level on the baoia of said measured grey levelo.
6. A static Indentation~ hardness testing machine as aimed in claim 5, wherein the caloulated maan grey level is compared with two predetermined grey levels forming the end-points or a predetermined range, and, 11 1 if the calculated mean grey level is outside the 2 predetermined range, the light output of the illumination 3 means is increased or decreased as appropriate. 4 7. A static indentation hardness testing machine according to any one of the preceding claims, the machine 6 further including a measurement apparatus for comparing the 7 size of the indentation with that of a reference object, the 8 apparatus comprising:- 9 a means for forming an image of the indentation whose size is to be determined, when the sample is in a viewing 11 position; and 12 a reference object, mounted in the apparatus, which may 13 be viewed, using the means for forming an image, instead of, 14 or in addition to, the sample. 13 8. A machine as claimed in claim 7, wherein the i6 indentation, the size of which is to be measured, and the 17 reference object may be viewed via a beam splitting mirror, 18 and are located such that an image of one is obtained by 19 transmission of light through the beam splitting mirror and 20 an image of the other is obtained by reflection of light 21 from the beam splitting mirror. 22 9. A machine as claimed in claim 7 or 8, wherein the 0* e• 23 object whose size is to be determined is located at the 24 viewing position, which is located in a focal plane of a camera lens, and illuminated, while the reference object is 26 also located in a focal plane of the camera lens, and is 27 illuminated, and hence viewed through the camera, only when 28 there is no object in the viewing position. 9 /w9 10. A static indentation hardness testing machine as 891031, psspe013,austin.res, LL 3 rr i r I c 12 claimed in one of claims 7 to 9, wherein the reference object comprises an image of a hardness test indentation, etched onto a transparent surface, and is mounted in the machine such that it is viewed from a first side thereof and is illuminated from the side thereof.
11. A static indentation hardness testing machine substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings. *r S DATED THIS 31st October, 1989 SMITH SHELSTON BEADLE Fellows Institute of Patent Attorneys of Australia. Patent Attorneys for the Applicant CHARLES THOMAS AUSTIN 8 91031,!psspeOl3,austin.res,