BRIGHTNESS ANALYSER

Abstract: Apparatus for determining a number of aggregates each of which is representative of the sum of areas of regions of a corresponding particular brightness in an image scanned by a scanning electron microscope. The apparatus includes a chopper (24) which from each line signal generated by the scanning electron microscope generates a train of pulses the amplitudes of which pulses are representative of respective instantaneous signal strengths in the line signal at time spaced intervals. Accumulations of pulses are made in a pulse height analyser having a number of counters (C<u0>u, C<u1>u, C<u2>u...C<un>u), the accumulation of pulses of a particular pulse height appearing in a particular one of said counters and thereby representing a particular one of the area aggregates. The chopper (24) is controlled by an oscillator (30) operation of which is itself controlled by a logic circuitry including a comparator (38) and a gate (31) to be responsive to a signal indicative of whether the scanning electron microscope is operating and to an externally applicable control signal. The line signals are separately routed via a summing amplifier (45) to the visual display device (10a) of the scanning electron microscope in a manner permitting superimposition of selected ones of the aforementioned pulses onto the line signals, for delineating in the visual display device image of regions of a selected brightness.

Description: "BRIGHTNESS ANALYSER" This invention relates to apparatus for use in image analysis. Techniques involving analysis of images for the purpose of determining the -total area of regions of a particular brightness within the image are well-known. These techniques may be used, for example, in analysis of images derived from a scanning electron microscope-or other.apparatus generating an image signal made up of line signals derived by scanning an object. More particularly, a known technique for analysis of the relative proportions of particular chemical or other components in a sample makes use of an image derived by a scanning electron microscope • An assessment of the total area represented by all parts of the image having a particular brightness may be made with a view to determining the percentage in the sample of a particular chemical component or physical phase represented by that brightness. Clearly, to perform this manually, by visual inspection and measurement of individual regions of the image, is time consuming. Data processing techniques are also known for making this assess¬ ment. For example analogue signals from success- ive scans by the scanning electron microscope may be recorded and subsequently analysed to detect and integrate specific signal strength or brightness values. Generally, these processes require dedicated computer facilities of some sophistication, and even though the amount of data 5 storage space required to store the image data can be minimised by the relatively sophisticated data selection and storage techniques, relatively expensive storage and processing apparatus is nevertheless required. One object of the inventio 10 is therefore to provide apparatus, usable with a "' - *"■• : scanning electron microscope or other apparatus producing image information in the form of line signals, to facilitate assessment of the total area of a particular brightness in the scanned 15 image and which does not require sophisticated computerised data processing and recording apparatus. In accordance with one aspect of the invention there is provided apparatus- for 20 receiving line signals representing the variation in brightness along respective successively displaced scans across an image and for use in determining from said line signals the total area of regions of a selected brightness in said image; 25 said apparatus comprising pulse generator means in use receiving said line signals and producing from each line signal a respective train of pulses, the amplitudes of which pulses are representative of respective instantaneous signal 30 strengths i n the line signal at time-spaced intervals. The pulse generator means may comprise a chopper in use receiving the line signals, said chopper being controlled via an oscillator so that the said pulses are generated from each line signal via respective gatings of the line signal through the chopper for fixed periods at successive time-spaced intervals under control of the oscillator. Means may be provided for adding a pulse signal to a said line signal pursuant to receipt of a first signal indicative of existence of a particular brightness- at a location i said image, as represented by a particular instantaneous signal level in the lastmentioned line signal, as scanning across the location occurs; said means operating to produce from the last mentioned line signal a modified line signal which when applied to generate a corresponding visual line display will cause appearance in that line display of a point region of substantially varied brightness ' as compared with immediately surrounding regions in the display, said point region being located in correspondence with said particular location. The apparatus may further include control means for receiving an indication signal which, in a first condition,is indicative of operation of a line signal generator to scan said image and generate said line signals and, in a second conditio is indicative that the line signal generator is not in operation; said control means operating when sai indication' signal is in said first condition- to enab output from said oscillator and, when the indication signal is in said second condition, to inhibit outpu from said oscillator. The apparatus may in this cas further include means such as an AND gate arranged t receive said indication signal and a further control signal so that output from the said oscillator is in hibited or enabled under selected condition ' s of both indication signal and control signal. Pulses derive from said pulse generatormeans may be applied to a pu height analyser of the kind providing at least one output indicative of the number of pulses applied thereto which are of a particular pulse height. Normally, the said pulse height analyser will have a plurality of outputs to indicate the numbers of pulses of various particular amplitudes applied to the analyser, and the invention contemplates the combination of said apparatus, together with said pulse analyser connected thereto to receive said pulses. In such a case, where the pulse analyser, is of kind which produces an output pulse whenever a pulse height of particular selected height is received, that output pulse from the said pulse analyser may comprise the said first signal. The invention further contemplates the combination of the said apparatus for receiving line signals and said pulse analyser, together with a scanning electron microscope or other apparatus for producing said line signals connected to supply said line signals to said apparatus for receiving line signals, and a visual display device connected to receive the said line signals- or said modified line signal. In such a case, the apparatus for producing said line signals may produce the said indication signal. The invention is further described by way of example with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of an apparatus constructed in accordance with the invention; Figures 2A, 2B, 2C, 2D and 2E show various wave forms referred to in the following description of the apparatus of Figure 1; Figures 3A and 3B show, respectively, an image as viewed by a scanning electron microscope, and a graph of pulse'counts against grey level intensity as derivable from " information stored in a pulse height counter forming part of the apparatus of Figure 1 pursuant to analysis of the image of Figure 3A; and Figure 4 shows a scanning electron microscope image like that in Figure 3A, but illustrating marking of areas of selected image greyness, as effected by the apparatus of Figure 1. In Figure 1 there is shown diagrammatically a scanning electron microscope 10, an interfacing apparatus 12 constructed in accordance with the invention and a pulse height analyser 14. The scanning electron microscope 10 is of conventional form producing, on an output line 16, a series of line signals corresponding to respective scanned lines of the image received by the microscope. A typical line signal 40 is shown in Figure 2A, this varying in amplitude in accordance with the variation in instantaneous image brightness as O PI &?N AT l - sensed by the microscope during a corresponding image scan. As previously described the scanning electron microscope 10 operates to scan the sensed image along successively displaced paths so that the corresponding scan lines appear successively on line 16. The microscope includes a visual display device 10a such as a cathode ray tube together with associated circuitry which, on receipt of line signals on an input line 18, causes display of successive lines of the scanned image to build up a corresponding image on the display device. Normally, the lines 16 and 18 would be interconnected to provide a direct display of the image received by the scanning electron microscope. However, as described later, the additional apparatus 12 and pulse height analyser 14 are in this instance separately connected between lines 16 and 18. The scanning electron microscope 10 -also has a further output line 20, referred to later, which has zero signal thereon when the microscope is not in use for scanning an image f but which has a positive supply applied thereto during scanning. The apparatus 12 of the " invention includes a chopper 24 which is coupled, as- shown, to the output line 16 via a buffer amplifier 26 and a non-inverting amplifier 28. The amplifier 28 operates to effect smoothing of the line signals 40 as. well as amplifying them to produce from each scan line signal a signal of the form shown at 42 in Figure 2B. The chopper 24 is controlled by a pulse generator 30 which in use applies repetitive pulses 43, of the form shown in Figure 2C through an AND gate 32 to the chopper 24. Chopper 24 is of a . kind which., on receiving pulses from generator 30 through gate 32 operates to generate at the chopper output a train of pulses 44 (Figure 2D) of heights representative of the instantaneous 5 magnitude of the signal 42 applied to the chopper from amplifier 28 at the respective times of the pulses from the generator 30 through gate 32.The trains of pulses from chopper 24, generated from successive line signals, appear successively 10 on a line 34 from the chopper. Oscillator 30 is a TTL pulse generator, the generated pulses 43 being of one microsecond width as shown. In Figure 2D pulses 44 -labelled ' (i) , (ii) , (iii) , (.iv) , are of height 15 -equal to the.-instantaneous amplitude, of the signal 43 at the times I, II, III etc. in Figure 2B. The pulse height analyser 14 is a commercially available type having a number of 20 channels and associated counters C Q , C, , C-.-.C , and the analyser including switching means oper¬ ative, on receipt of a pulse 44 from chopper 24 to increment a particular counter. Thus,there may be several hundreds of channels, the counter 25 of each channel being arranged to be incremented when pulse heights in a particular limited range unique to that channel are received. It will be seen therefore that the count in a particular channel counter at the end of'a scanning (i.e. 30 at the termination of a set of line signals from the microscope) will be representative of the total number of pulses received during the scan period which are within that channel counter's unique range of pulse heights. Since the height of a pulse 44 is proportional, by virtue of the analogue nature of the line signals, to an instantaneous brightness level in the image scanned by the micro¬ scope, the end count represented by such a channel counter will be proportional to the total area in the image of all regions of a particular brightness. In order to illustrate the operation of the apparatus 12 reference is now made to Figures 3A and 3B, Figure 3A shows a typical image as built up from line signals from scanning electron microscope 10. The image comprises a number of distinct areas distinguished from each other by variations in brightness. The regions designated region 2 are each of a similar grey level. The regions designated region 3 are of equal grey level greater than that of regions 2 and region 1 is of lower greyness level than regions 2. For each of the grey levels corres- ponding to regions 1,2 and 3 there will be generated, by the apparatus 12 a number of pulses 44 of height unique to the particular grey level of each region. In the present instance, since there are but three distinct grey levels, a plot of the count for each possible pulse level resolvable by the pulse height analyser 14 against grey level intensity will appear as shown in Figure 3B. That is to say, there will be distinct peaks in the count at the three distinct grey levels of the various regions in the image and the heights of these peaks will be proportional to the respective total areas in the image of the regions 1, 2 and 3 respectively. As shown, the region 1 is clearly of the greatest area and thus its corresponding peak in the graph of Figure 3B is highest. The combined regions 3 are of lowest total area and the corresponding peak in the graph is lowest. By suitable interrogation of the out¬ puts from pulse height analyser 14, it is, of course, possible to provide a visual display, on a visual display device,of the graph shown in Figure 3B. In order to ensure that pulses 44 from the chopper as counted by the analyser 14 are truly representative of brightness levels sensed only during scanning, means is provided for inhibiting the chopper 24 during periods where scanning does not take place. Thus, by resetting pulse height analyser so that each channel has zero count therein and then ' -beginning operation of the scanning electron micro- scope at any designed time thereafter the chopper is brought into operation only when scanning actually commences, and will be inhibited again when scanning is complete. This is effected by controlling gate 32 in accordance with- the voltage on the line 20. More particularly, the line 20 has a resistor connected thereto, the end of the resistor remote from the line 20 being connected through an AND gate 31 to the non-inverting input of an amplifier 38. A zener diode 49 is connected in parallel with a capacitor 46 between ground and the non-inverting terminal of amplifier 38 and this diode, in combination with the resistor 36, serves to drop voltage from a 24 volt normal supply on line 20 to a 5 volt signal suitable for use with the amplifier 38. When signal appears on line 20, and gate 31 is enabled as described later, amplifier 38 is switched on and the output of amplifier 38 is connected to gate 32 so as to turn the gate 32 on for passage of pulses from the generator 30 to chopper 24. When signal is. not present on line 20, amplifier 38 is correspondingly turned off and gate 32 is inhibited. As mentioned, the line 20 has a voltage thereon only during scanning so that the described inhibiting of pulse counting outside scanning periods is effected. Gate 31 has two inputs, one of which receives the aforedescribed signal from line 20, via resistor 36. The other input is connected, on the one hand, to positive supply via a resistor 37 and, on the other hand, to an "auxiliary" terminal 33. If nothing is connected to terminal 33, the corres¬ ponding input of gate 31 is maintained in an ON condition by virtue of the connection thereof to positive supply via resistor 37. However, it is possible to connect suitable additional control apparatus to terminal 33 so as to short this terminal to ground under selected control conditions to disenable gate 31 so that gate 32 is disenabled to correspondingly inhibit application of pulses from generator 30 to chopper 24. Terminal 33 may be connected to any desired control apparatus. It has been found advantangeous to arrange for the terminal 33 to be connected to an X-ray detector forming part of the scanning electron microscope 10. This detector is arranged to ground terminal 33 and disable gate 31 when a sample being examined by the microscope causes the detector to detect one or more particular elements in the sample. Thus, inhibition of pulse counting can be arranged to occur when the scanning electron microscope is scanning areas of a sample image which are judged to be of no interest on the basis of indications of the elemental composition over those areas. The aforementioned visual display device of the scanning electron microscope is- arranged to receive line signals from line.16 via the afore¬ mentioned buffer amplifier 26, an inverting buffer amplifier 39, having its input connected to the output of that amplifier 26, and a summing amplifie 45. The summing amplifier 45 has one input connected to the output from amplifier 39 and the output connected to line. L8 to the visual display device ' and the scanning electron. mi.croscope. The other input to summing amplifier 45 i:s- connected vi a switch SI to the. output of a. pulse stretcher 47, the pulse stretcher in turn having its input connected to a "single channel" .output terminal 51 of analyser 14. Terminal 51 is a terminal of analyser 14 at which a pulse appears whenever a pulse is delivered to the analyser on line 34 which is of a pre-selected pulse height. When this occurs, the pulse is stretched from its relatively short duration to a rather longer duration of some 20 microseconds in length, by the pulse- stretcher 47 and, assuming switch SI between the pulse stretcher and summing amplifier 45 is closed, such stretched pulse is then passed to the summing amplifier together with the line input from amplifier 39. The effect of this is to superimpose upon the. instantaneous analogue line voltage present on line J.6 at " the time a further pulse from the pulse stretcher. Several further pulses, designated by reference numerals 53 ,are shown in Figure 2E. Thus, the arrangement is such that whenever a pulse of the desired pre-selected height is detected, on line 34, a corresponding further pulse is generated which is applied to raise the instantaneous signal level of the line signal as passed through the summing amplifier 45. The raised signal level causes appearance of a spot in the visual display of the particular line in question so brightening the display at this point. Since there is negligible time delay through the pulse height analyser, the spot appears at a point in the displayed image which corres¬ ponds to the point at which the brightness of the image as seen by the electron microscope was at a predetermined level corresponding to the predetermined pulse height level for operation of the pulse height analyser to cause output of a pulse on line 51. This has been found to facilitate visual inspection of the image from the scanning electron microscope in that areas of preselected brightness aredelineated by 'a matrix of dots of higher brightness caused by the super¬ imposed further pulses 53 on the line signal. Figure 4 illustrates in a schematic way the use of the ' apparatus 12 for delineation by a dot matrix 6 of the areas comprising the regions 2 in the image shown in Figure 3A. This is effected by simply arranging for pulses to appear on line 51 when¬ ever they are of height corresponding to the grey level intensity of region 2 (i.e. at the grey level corresponding to the peak marked "2" in Figure 3B) . The single channel analyser output 51 can be arranged, by suitable control circuitry included in the analyser, to permit a pulse to appear at terminal 51 whenever a pulse ' in any desired range of pulse heights arrivesat analyser 14. Thus, the controls of the analyser may be set so that all pulses passing to the analyser on line 34 cause generation of pulses 53, whereupon the whole of the image seen by the visual display- device will be covered by dot matrix. On the other hand, the range of input pulse heights which will cause generation of pulses at 5 terminal 51 may be adjusted so as to occur over any lesser range of the pulse heights received by the analyser, such those close to one particular pulse, height/ as mentioned, or those close to any number of adjacent height ' s. The ability to 10 vary this acceptance range of input pulse heights to analyser 14 for which pulses will appear at terminal 51 permits a check to be made by an operator seeking to adjust the apparatus 12 to provide the described dot matrix shading of the 15 image over regions where the brightness falls within fine limits. This is particularly valuable where grey tones apparent in the visual display are close in brightness to each other and it is desired to adjust the apparatus for 20 very accurate outlining of the boundaries of a region in the image possessing a desired bright¬ ness. The described invention has been found to be particularly satisfactory in use, being simple 25 in construction and relatively inexpensive. In this regard, although a pulse height analyser could be built into the apparatus, it is normal in laboratories concerned with electron micro¬ scope to utilize pulse height analysers for other 30 purposes and thus the pulse height analyser may already be present and require only connection via the apparatus 12. In this regard, commercially available types of pulse height analysers are quit suitable for use with apparatus 12 without 35 modification. The described apparatus 12 enables > rapid on-line measurement of areas of an image selected according to grey tone or brightness without in any way modifying the scanning system of the scanning electron microscope and without requiring recourse to processing photographic or other stored records of the image. It will be observed in this respect that the operation of the apparatus can be so arranged as to avoid modification of the image from the scanning electron microscope in any way. Furthermore, no modification of the electronics of the scanning electron microscope other than the provision of an output parallel to the normal detector output and if necessary the separate provision of a voltage level of greater than five volts from the " photo- - graphic "record" output of the. scanning electron microscope is required. The described arrangement has been advanced merely by way of explanation. For example, whilst the pulse generator 30 is in the described embodiment a TTL pulse generator, it is of course possible to use CMOS or other integrated circuits for the pulse generator and also for the pulse stretcher 47. The described apparatus 12 may also use a microprocessor interface. Such an interface could be arranged to control both the microscope 10 and the pulse height analyser, and in any event could replace all of the digital circuits of apparatus 12 including at least the TTL pulse generator 30 and pulse stretcher 47.

Claims: - 16 - CLAIMS : 1. Apparatus for receiving line signals representing the variation in brightness along respective successively displaced scans across an image and for use in determining from said line signals the total area of regions of a selected brightness in said image; said apparatus comprising pulse generator means (24, 30) in use receiving said line signals and producing from each line signal a respective train of pulses, the amplitudes of which pulses are representative of respective instantaneous signal strengths in the line signal at time-spaced intervals. 2. Apparatus as claimed in claim 1, wherein the pulse generator means comprises a chopper (24) in use receiving the line signals, said chopper being controlled via an oscillator (30) so that the said pulses are generated from each line signal via respective gatxngs of the line signal through the chopper (24) for fixed periods at successive time-spaced intervals under control of the oscillator. 3. Apparatus as claimed in claim 2, wherein adding means (45) is provided for adding a pulse signal to a said line signal pursuant to receipt of a first signal indicative of existence of a particular brightness at a location in said image, as represented by a particular instantaneous signal level in the last mentioned line signal, as scanning across the location occurs; adding means ( . 451 operating to produce from the last mentioned line signal a modified line signal which when applied to generate a corresponding visual line display will cause appearance in that line display of a point region of substantially varied brightness as compared with immediately surrounding regions in the display, said point region being located in correspondence with said particular location. 4. Apparatus as claimed in claim 2 or claim 3 , including control means (31, 38) for receiving an indication signal which, in a first condition, is indicative of operation of a line signal generator to scan said image and generate said line signals, and, in a second condition, is indicative that the line signal generator- is not in operation; said control means (31, 38) operating when said indication signal is in said first condition to enable output from said oscillator (30) and, when the indication signal is in said second condition, to inhibit output from said oscillator (30) . 5. Apparatus as claimed in claim 4, including means (31) arranged to receive said indication signal and a further control signal so that output from the said oscillator (30). is inhibited or enabled under selected conditions of both the indication signal and control signal. 6. In combination, apparatus as claimed in any preceding claim together with a pulse height analyser (14), said pulse height analyser (14) being connected to receive said pulses from said pulse generator means (24, 30), said pulse height analyser (14) being of the kind providing at least one count indicative of the number of pulses applied thereto which are of a particular pulse height. 7. The combination claimed in claim 6 as appended directly or indirectly to claim 3, wherein said pulse height analyser (14) is of a kind which produces an output pulse whenever a pulse height of particular selected height is received, said puls height analyser being connected whereby the last mentioned output pulse from the said pulse analyser comprises the said first signal. 8. The combination claimed in claim 8, togethe with a scanning electron microscope (10) or other apparatus for producing said line signals connected to supply said line signals to said apparatus for receiving line signals, and a visual display device connected to receive the said line signals or said modified line signal. 9. The combination claimed in claim 8 as append indirectly to claim 4. wherein said apparatus for producing line signals operates to produce said indication signal.

Inventors: HARROWFIELD I
Applicants: COMMW SCIENT IND RES ORG, HARROWFIELD I
Application year: 1981
Main classification: H04N7
IPC codes: G01D1, G01N15, H01J37