GB2038063A - Bank note identification - Google Patents

Abstract

Apparatus for identifying the denomination of a bank note comprises a sensor 14 which senses light reflected from an incremental area 16 of a bank note 10 to produce an output which is passed to a storage 24 at intervals. When sufficient sample outputs have been stored in the storage 24 a control 28 causes each sample to be compared in a comparator 30 with a number of previous samples taken in a pre-selected sequence so as to produce a multi-bit correlation number. Each correlation number thus formed is then compared with reference multi-bit numbers derived from scanning a corresponding section of a number of notes of the different denominations to be identified. If the multi-bit number derived from the scanning is the same as any of the reference multi-bit numbers, a correlation count for that particular denomination is incremented. This process is repeated for the whole area of the note and, on completion, the correlation counts for the different denominations are compared. Provided the ratio of the largest correlation count to the next highest correlation count is 1.28 or greater and the largest correlation count is at least 28, the note is identified, as shown by an indicator 36. <IMAGE>

Description

SPECIFICATION Bank note identification The invention relates generally to automated banking equipment and particularly to an automatic currency discriminator for currency counting machines and the like.

In the field of automated banking, many sophisticated machines have been developed in recent years which are useful in automating many of the heretofore manual operations performed in the banking industry. Of particular concern has been automated equipment for identifying the denomination of currency.

Many of the existing techniques are either excessively complicated, making high speed verification difficult, or they lack the required accuracy for application in the banking industry.

Furthermore, those approaches which are complicated also suffer from being rather costly to implement, regardless of operation speed.

It is, therefore, a principal objective of the present invention to provide a currency discriminator particularly useful in high speed automated banking devices such as currency counters.

According to the present invention, the denomination of a bank note or the like is identified by a method in which a source of light is directed onto one surface of the bank note whose denomination is to be determined, the reflectance of light from a number of incremental areas disposed along the length of the bank note is measured, the reflectance of light from each incremental area is compared with the reflectance of light from each of a preselected number of other incremental areas taken in a pre-selected sequence so as to produce a first correlation signal responsive to the comparison for each incremental area and the first correlation signals are compared with respective second reference correlation signals corresponding to each denomination required to be identified so as to determine the denomination of the bank note.

Apparatus for this purpose, in accordance with the invention, comprises means to produce a signal p, whose magnitude is proportioned to the reflectance of light from an area of a bank note, means to store a representation for the reflectance of light from each of a plurality of different areas on the bank note, means to form a plurality of multi-bit correlation numbers N, where the first bit of each number is a one if Pn > Pn-2 but otherwise it is a zero, the second bit of each number is a one if Pn > Pn-4 but otherwise the second bit is zero, the third bit of each number is a one if Pn > Pn-6 but otherwise the third bit is zero and the fourth bit of each number is a one if Pn > Pn-8 but otherwise the fourth bit is zero, where p, is the stored representation for the reflectance of light from a given area, Pn-2 is the stored representation for the reflectance of light from the second previous given area, Pn-4 is the stored representation for the reflectance from the fourth previous given area, Pn-6 is the stored representation for the reflectance from the sixth previous given area and Pn-8 is the stored representation for the reflectance from the eighth previous given area, means for comparing each said multi-bit correlation number n with a multi-bit number which corresponds to the same four bit number derived from a sample note of each denomination of bank note detected by the apparatus and, on a favourable comparison, for incrementing a denomination count for the corresponding denomination, and means for producing an identity signal correlated to the identified denomination if the denomination count for such denomination is at least equal to 28 and is at least 1.28 times any other denomination count.

The invention will now be described in more detail, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of electronic circuitry for a currency discriminator according to the present invention; Figure la shows a sensor of Fig. 1 in diagrammatic form; Figure 2 shows the manner in which the control circuit of Fig. 1 is operable to cause the remaining circuitry to form a multi-bit correlation number N; Figure 3 shows the manner in which the control operates the remainder of the equipment so as to determine the largest correlation number N; Figures 4a, 4b and 4c show how the controls determine whether the largest correlation count is equal to or greater than 1.28 times the next largest correlation count; Figure 5 is a system block diagram for the preferred form of discriminator;; Figure 6a is a front view of a sensor used in the preferred form of discriminator; Figure 6b is a plan view corresponding to Fig. 6a; Figures 7A and 7B are wiring diagrams; Figure 7 shows how the wiring diagrams of Figs. 7A and 7B fit together; Figure 8 shows a voltage regulator for the system; Figures 9A and 9B show an analogue signal processor; Figure 9 shows how the analogue signal processor of Figs. 9A and 9B fit together; Figures 1 0A and 10B show a main processor; Figure 10 shows how the main processor of Figs. 1 0A and 1 OB fit together; Figures 1 1A and 118 show a digital signal processor; and Figure 11 shows how the digital signal processor of Figs. 1 1A and 11 B fit together.

In the diagram of Fig. 1, a bank note 10 is shown as being transported in the direction of the arrow 1 2 past a bank note sensor 14 which is arranged so that an area on the bank note, indicated at 16, is illuminated and the light reflected therefrom is sensed by the sensor 1 4. The sensor 14 is a light intensity sensor which outputs a digital representation for light which strikes it.

One form of sensor is shown in greater detail in Fig. 1A wherein the bank note 10 again travels in the direction of the arrow 1 2. A light source 1 8 illuminates the surface of the bank note 10 so that light is reflected therefrom through a shield assembly 20 to a light sensor 22.

The shield assembly 20 is physically arranged with respect to the light sensor 22, the light source 1 8 and the bank note 10 in such a manner that light reflected from a rectangular area approximately 2 mm X 80 mm on one side of the bank note 10 is detected by the light sensor 22. The analogue output of the light sensor 22 is placed on the line labelled video which, as is described in greater detail below, is stored in a storage device 24, as shown in Fig. 1.

In addition to providing an analogue output correlated to the reflected light from a rectangular area on the bank note 10, the sensor 1 4 includes a bank note distance-travelled sensor which will produce a pulse each time the bank note 10 travels a known distance such as 1 mm in the direction of arrow 1 2. One means for implementing such a sensor is to provide two rollers 26 of known dimensions which are urged toward each other to form a nip for the passage of the bank note 10, as illustrated. One of the rollers 26 is coupled to a rotation sensor including a disc with holes or slots in it through which light may pass. A photo sensor co-operates with the disc to produce an electric pulse each time the roller 26 turns through a predetermined angle.By properly selecting the dimensions of the rollers 26 as well as the slotted wheel, such an arrangement can produce a pulse every time the bank 10 travels a distance of 1 mm.

The distance-travelled pulses from the circuitry shown in Fig. 2 are utilised by the control 28 of Fig. 1 to determine when the video should be sampled to make certain that a different area is sampled than was previously sampled. For the arrangement where it is desired to determine the reflectance of light from an area 2 mm X 80 mm and the distance-travelled pulses occur once for every 1 mm of note travel, every other pulse from the rotation sensor of Fig. 1 a is utilised to cause the video output to be stored in the storage 24.

The circuit of Fig. 1 additionally includes a comparator 30 for producing a signal on its output line 32 whenever the input to terminal A is greater than that at terminal B. Such comparators are well known and need not be described further.

The circuit of Fig. 1 also includes an incrementor 34 whose operation is directed by the control circuit 28 to increment a number received from the storage 24 and add one to that number and return it to storage 24. The system of Fig. 1 further includes a multiplication unit which is operative to multiply data received from the storage 24 under the direction of the control circuit 28 to produce a number which is 1.28 times greater than that input to the multiplier 32. Incrementor and multiplication units are also well known and, therefore, need not be described.

The circuit of Fig. 1 also includes an indicator 36 which is coupled to the control 28 and responds thereto to indicate the identity of the denomination of the bank note 10.

In operation, the circuitry of Fig. 1 is first operative to store a decimal representation of the output from the sensor 14 into the storage 24. This is accomplished by means of the fact that every other pulse received from the rotation sensor in Fig. 1 a causes a digital representation to be stored in the storage 24. For present day United States Federal Reserve Notes, once seventy two such samples have been taken across the reverse side of the bank note 10, sufficient data is available in the storage 24 to determine the denomination of the note itself. It should be noted that the reverse side of the note, i.e. the side of a note not containing a portrait, is utilised for denomination discrimination because it contains more information relevant to the denomination of the note than does the front side.

When at least nine samples p, (where n is an integer between 1 and 72) have been stored in the storage unit 24, the control 28 is operative in a manner shown in Fig. 2 to operate the systems to generate a plurality of multi-bit correlation numbers N. As shown in Fig. 2, n is first set to 8 and then incremented to 9. Then the digital representation for the sample pg is compared with the second previous sample, i.e. sample p7. If p9 is greater than or equal to p7, a 1 is set in the first bit position for correlation number one. On the other hand, if p9 is less than p7, a zero is placed into bit position one of correlation number one. Thereafter pg is compared with the fourth previous sample p5 and if the former is greater than or equal the latter, a 1 is set into the second bit position of correlation number one. On the other hand, should p9 be less than p5, a zero is placed into the second bit position of correlation number one.

Next the control 28 determines whether p9 is greater than or equal to the sixth previous sample p3. If it is, a 1 is placed into the third bit position of correlation number one and if it is not, a zero is placed into the third bit position of correlation number one. Thereafter the control 28 determines whether p9 is greater than or equal to the eighth previous sample p1. If it is, a 1 is set into the fourth bit position of correlation number one and if it is not, a zero is placed into the fourth bit position of correlation number one.

Thereafter the control 28 determines whether n is equal to 72 which would be the case if all the available data had been utilised to form correlation numbers. It will be observed, however, that only sixty four correlation numbers are formed because at the outset of the sequence shown in Fig. 2, n is set to 8 so that only sixty four such correlation numbers can be generated for each bank note tested. If it is determined that n is not equal to 72, then n is incremented and a further correlation number is formed in accordance with the sequence as shown in Fig. 2. On the other hand, if n is equal to 72, all sixty four correlation numbers have been formed and the control 28 can move on to determining whether the correlation numbers are equal to previously stored correlation numbers for known denominations.The control sequence for determining the equality of correlation numbers is shown in Fig. 3.

Referring now to Fig. 3, the control 28 first causes a number N to be set to zero and subsequently incremented by one. Thereafter, the correlation number N is fetched from memory. Subsequently, the correlation numbers N1, N5, N10, N20, N50 and N100, which correspond to the expected correlation numbers for respectively $ 1.00, $5.00, $ 10.00, $20.00, $50.00 and $100.00 notes are fetched from memory as weil. Then the current correlation number N is compared with the corresponding correlation number N, for a $ 1.00 bill. If the two are equal, a $ 1.00 count is incremented. In either case, however, the control then jumps to a comparison of the current correlation number N with the corresponding correlation number N5 for a $5.00 note. If correlation number N equals correlation number N5, the $5.00 count is incremented.If not, the control jumps to a further comparison of the current correlation number N with the correlation number N,O. The process continues in the manner shown in Fig. 3 whereby the current correlation number N is compared with a corresponding correlation number for each particular denomination which the apparatus is capable of identifying. If the current correlation number N is equal to a corresponding correlation number Nx, the corresponding determination count is incremented.

Once the current correlation number N has been compared with all corresponding correlation numbers Nx, the control checks to determine whether N is equal to 64. If not, the process is repeated for a subsequent value of N.

On completing the sequence of events shown in the flow chart of Fig. 3, the system according to Fig. 1 has a $1.00, $5.00, $10.00, $20.00, $50.00 and $100.00 count where the count indicates the number of times that one correlation number N corresponded to a corresponding correlation number Nx for that particular denomination of bank note.

It should be noted that the above analysis assumes each note is either right side up or upside down as it passes the sensor. The system can be expanded easily to check for notes which are not always arranged the same way, i.e. the notes may be either upside down or right side up.

This added feature is accomplished by comparing the current correlation number N with all corresponding correlation numbers Nx for notes right side up and with a further set of corresponding correlation numbers Nx for notes upside down. It will be recognised that this modification may also be adapted to permit the system to identify other denomination notes such as the $2.00 note.

Statistical analysis had demonstrated that when the largest count, as determined by the sequence shown in Fig. 3, is at least 1.28 times larger than the next largest count and is at least equal to 28, then the bank note corresponds to that identified by the particular denomination count which is largest. For sample, if the $5.00 count is at least 28 and at least 1.28 times greater than the $1.00, $10.00, $20.00, $50.00 and $100.00 count, then the denomination of the note under test is a $5.00 note.

One sequence for determining whether a given count is at least 28 and at least 1.28 times greater than any other count for a particular bill is shown in Figs. 4a, 4b and 4c. A sequence like that shown in Fig. 4a determines which of the counts is the largest. By tracing through the decisipn blocks of Fig. 4a, it will become apparent that if the control exits at point A, the $ 1.00 count is the largest. On the other hand, exiting at points B, C, D, E and F respectively corresponds to the $5.00, $10.00, $20.00, $50.00 and $100.00 counts being the largest. A similar decision sequence is required if notes are both right side up and upside down.

Referring now to Fig. 4b, when the control determines that the $ 1.00 count is the largest, then a determination must be made as to whether the $ 1.00 count is larger than or equal to 1.28 times the next largest count. The sequence shown in Fig. 4b checks whether the $ 1.00 count is greater than 1.28 times all the other counts. In this manner, if the answer is yes to each check, and if the count is at least 28, it is certain that the note is a $ 1.00 note. The indicator is then actuated to indicate the note identity as a $ 1.00 note. If the $ 1.00 count is not at least 1.28 times all other counts, then the bill cannot be identified with sufficient accuracy and the indicator 34 is actuated to indicate that the note cannot be identified.

In a similar manner, the control as depicted in Fig. 4b is operative when the $5.00 denomination count is the largest to compare the $5.00 count with the $1.00, $10.00, $20.00, $50.00 and $100.00 count. If the $5.00 count is at least 1.28 times the $1.00, $10.00, $20.00, $50.00 and $100.00 count and is at least 28, then the note is a $5.00 note and the indicator 34 is actuated to indicate this.

The control 28 operates in a manner depicted in Fig. 4c to produce an indication that the note is a $10.00, $20.00, $50.00 or $100.00 note where the corresponding count is at least 28 and at least 1.28 times all the other denomination counts for the particular note being tested. If the largest count identified by the sequence shown in Fig. 4a is not at least 1.28 times the next largest count, or not at least 28, the note cannot be identified and the indicator 34 is actuated to indicate the same.

It will be recognised that the sequence for the control 28 as shown in Figs. 2, 3, 4a, 4b and 4c can be modified somewhat from that shown to achieve the same result with the circuitry shown in Fig. 1. In addition, it will be recognised that the discrimination of denomination in accordance with the present invention may readily be implemented by a circuit configuration different from that shown in Fig. 1 but which will achieve the same objective. For example, a system as depicted generally in Fig. 5 will operate in the manner described above to produce the same tests as that described above, although the specific details of the circuit operation are quite different. The circuit according to Fig. 5 includes at least two lamps 50 disposed in a position to illuminate a note 52 as it moves past the lamps 50 in a direction indicated by the arrow 54.The light reflected from the note 52 is sensed by a detector 56 which may comprise a type 52C solar cell manufactured by Optical Coating Laboratory Inc. of City of Industry, California, United States of America. Disposed between the lamps 50 and the detector 56 is a shield 58 with a centrally disposed opening 60 through which some light reflected from the note 52 can pass. By correct location of the detector 56, the shield 58, the note 52, and by correct selection of the size of the opening 60, the detector 56 can be made to respond only to light reflected from a given area on the note 52. As indicated earlier, the dimensions are preferably such that an area of 2 mm wide and 80 mm high is "seen" by the detector 56.

A signal conditioning circuit 62 is coupled to the detector 56 and is for amplifying the analogue signal received therefrom. After amplification, the video received from the detector 56 is transmitted by the signal conditioning circuit 62 to the edge of an engraving detector circuit 64 and to a simple and hold circuit 66. The edge of engraving detector circuit 64 produces a signal at its output 68 once it has determined that engraving on the bank note is in view of the detector 56.

The sample and hold circuit 66 is conditioned by a timing and control logic circuit 70 by way of a control signal which is transmitted to the sample and hold circuit 66 on line 72. When the signal appears at the sample and hold circuit 66 on line 72, the analogue input to the sample and hold circuit 66 becomes stored therein. The analogue signal stored in the sample and hold circuit 66 is converted by an A/D converter 76, which is coupled thereto, into digitised video data which is transmitted by way of line 78 to a peripheral interlace circuit 80. When the micro-processor 82 is interrupted by the timing and control logic circuit 70 by an interrupt signal, the digital data in the peripheral interface circuit is transmitted to the micro-processor 82 which stores it in the random access memory (RAM) 84.

The micro-processor 82 is contrn-ed by the control information found within the read only memory (ROM) 86. The sequence of events performed by the micro-processor 82 is generally the same as described above. On completing the scan of the note, the micro-processor 82 indicates to the peripheral interface circuit 80 the identity of the bank note in the form of a denomination indication code.

The details of the content of the read only memory 86 is shown below in Table 1 which operates in connection with the detailed circuit diagram shown in Figs. 7 to 11.

Referring briefly to Figs. 6a and 6b, the detector arrangement is shown in more detail. The detector includes a pair of parallel spaced bracket members 100 which are joined by a substantially planar member 102. Centrally located in the member 102 is a slot 104 which, as viewed in Fig. 6a, is a narrow rectangular area disposed between the plurality of lamps 106 which, in operation, are turned on in order to illuminate the note 108 as it moves by the detector.

Table 1 STMT ADDR CONTENT STMT ADDR CONTENT STMT ADDR CONTENT STMT ADDR CONTENT 1 0000 OF 46 005D 59 91 00B3 27 06 136 00FF 97 1D 2 0001 B6 07 47 005E A6 08 92 00B5 A1 00 137 0101 D7 1E 3 0003 B7 4001 48 0060 A0 04 93 00B7 2E F6 138 0103 DB 1C 4 0006 86 OF 49 0062 26 01 94 00B9 20 F0 139 0105 99 1B 5 0008 B7 4002 50 0064 0D 95 00BB CE 0001 140 0107 97 1B 6 000B 86 04 51 0065 59 96 00BE 96 18 141 0109 D7 1C 7 000D B7 4003 52 0066 A6 08 97 00C0 44 142 010B 96 1D 8 0010 8E 007F 53 0068 A0 02 98 00C1 25 01 143 010D D6 1E 9 0013 4F 54 006A 26 01 99 00C3 08 144 010F 0C 10 0014 CE 0001 55 006C 0D 100 00C4 9C 17 145 0110 59 11 0017 A7 00 56 006D 59 101 00C6 26 02 146 0111 49 12 0019 08 57 006E A6 08 102 00C8 08 147 0112 0C 13 001A 8C 000F 58 0070 A0 00 103 00C9 08 148 0113 59 14 001D 26 F8 59 0072 2601 104 00CA DF 19 149 0114 49 15 001F CE 83FF 60 0074 0D 105 00CC A6 00 150 0115 97 1D 16 0022 DF 13 61 0075 59 106 00CE 08 151 0117 D7 1E 17 0024 00 1E 62 0076 53 107 00CF 08 152 0119 DB 1C 18 0027 DF 15 63 0077 DE 13 108 00D0 8C 000F 153 011B 99 1B 19 0029 DF 0F 64 0079 7F 001A 109 00D3 27 0F 154 011D 97 1B 20 002B CE 0026 65 007C 7F 0019 110 00D5 8C 0010 155 011F D7 1C 21 002E DF 11 66 007F 7C 001A 111 00D8 27 0A 156 0121 96 1D 22 0030 0E 67 0082 96 1A 112 00DA 9C 17 157 0123 D6 1E 23 0031 96 16 68 0084 81 0F 113 00DC 27 F0 158 0125 CC 24 0033 2B 04 69 0086 27 0F 114 00DE A1 00 159 0126 59 25 0035 81 1F 70 0088 08 115 00E0 2E EC 160 0127 49 26 0037 2D F8 71 0089 E1 00 116 00E2 20 E6 161 0128 DB 1C 27 0039 86 08 72 008B 26 0A 117 00E4 DE 17 162 012A 99 1B 28 003B B7 4002 73 008D DF 17 118 00E6 A6 00 163 012C 97 1B 29 003E 96 16 74 008F DE 19 119 00E8 81 14 164 012E D7 1C 30 0040 2B 04 75 0091 6C 00 120 00EA 2D 52 165 0130 DE 17 31 0042 81 27 76 0093 DE 17 121 00EC DE 19 166 0132 A6 00 32 0044 2D F8 77 0095 20 E8 122 00EE A6 00 167 0134 91 1B 33 0046 DE 11 78 0097 DF 13 123 00F0 5F 168 0136 2E 09 34 0048 9C 15 79 0099 DE 11 124 00F1 97 1B 169 0138 26 04 35 004A 27 FC 80 009B 8C 0066 125 00F3 D7 1C 170 013A D6 1C 36 004C 08 81 009E 27 03 126 00F5 44 171 013C 27 03 37 004D DF 11 82 00A0 7E 0048 127 00F6 56 172 013E 4F 38 004F DE 0F 83 00A3 0F 128 00F7 44 173 013F 20 02 39 0051 08 84 00A4 4F 129 00F8 56 174 0141 96 18 40 0052 DF 0F 85 00A5 B7 4002 130 00F9 44 175 0143 4C 41 0054 C6 0F 86 00A8 CE 0001 131 00FA 56 176 0144 44 42 0056 A6 08 87 00AB DF 17 132 00FB 44 177 0145 B7 4002 43 0058 A0 06 88 00AD A6 00 133 00FC 56 178 0148 20 FE 44 005A 26 01 89 00AF 08 134 00FD 44 45 005C 0D 90 00B0 8C 000F 135 00FE 56 As seen in Fig. 6a, the detector 110 is disposed on a bracket 11 2 which is fixed to the rear surface of the member 1 02. The detector 110 is positioned as viewed in Fig. 6a so as to permit light reflected from a bank note 108 to pass through the slot 104 and strike the detector 110 but light cannot hit the detector directly from the lamps 106.

As a result of the operation described above, the micro-processor 82 of Fig. 5 inputs 72 samples of digitised video data for each bank note that is scanned. Once this data is in the random access memory 84, the micro-processor 102 generates sixty four four-bit correlation numbers. The four-bit correlation number is created by taking four one-bit differences of the present sample p, as compared with the second previous, the fourth previous, the sixth previous and the eighth previous sample.In other words, the sample p, is compared with the second previous sample Pn-2, the fourth previous sample p-, the sixth previous sample Pn-6 and the eighth previous sample Pn-8 If the sample p, is greater than or equal to the sample Pn-2, a binary 1 is placed into the first bit of the four bit correlation number. If p, is greater than or equal to Pn-4, then a 1 is placed in a second bit of the correlation number. Where p, is greater than or equal to Pn-6, a 1 is placed in the third bit position of the correlation number.Further, if p, is greater than or equal to Pn-B, a binary 1 is placed into the fourth bit position of the correlation number.

Once all the four-bit correlation numbers have been generated, they are then compared with permanently stored four-bit reference correlation numbers representing the corresponding element of each denomination. If a match exists between the test correlation number and the reference correlation number, a correlation of that sample with the reference is said to exist and a correlation count for that denomination of bank note is incremented. There are a plurality of such tests performed for each sample and they correspond to one test for each denomination which can be discriminated by the apparatus when the note is right side up and a corresponding number when the note is upside down.

Once the last sample correlation number has been generated and compared with the corresponding reference correlation numbers, the micro-processor determines the denomination based on the following two criteria. If the ratio of the highest denomination count to the next highest denomination count equals or exceeds 1.28, then the denomination can only be that corresponding to the highest count. If this ratio is less than 1.28, the note is classified as being unknown. The second acceptance criterion is that the largest denomination count for the test note must equal or exceed 28. If both criteria are met, the micro-processor 82 actuates the peripheral interface 80 to produce a denomination identification code on the line so indicated.

Figs. 7 to 11 show in complete detail an implementation of a currency discriminator according to the present invention wherein all circuit types are given their parameter value or commercial designation for reader convenience and is not intended as a limitation on component value or type nor as a restriction on the scope of the invention.

Claims (9)

1. A method of identifying the denomination of a bank note or the like in which a source of light is directed onto one surface of the bank note whose denomination is to be determined, the reflectance of light from a number of incremental areas disposed along the length of the bank note is measured, the reflectance of light from each incremental area is compared with the reflectance of light from each of a pre-selected number of other incremental areas taken in a preselected sequence so as to produce a first correlation signal responsive to the comparison for each incremental area, and the first correlation signals are compared with respective second reference correlation signals corresponding to each denomination required to be identified so as to determine the denomination of the bank note.

2. A method of identifying the denomination of a bank note or the like, according to claim 1 in which a third signal is generated in response to the degree of correlation between the first correlation signals and the second reference correlation signals and the third signal is compared with a pre-selected standard to determine the reliability of the denomination determination of the bank note.

3. A method of identifying the denomination of a bank note or the like according to claim 2, wherein the third signal is generated in response to the degree of correlation by incrementing a denomination count when the first correlation signals correspond to the second reference correlation signals and determining and outputting, after all denomination counts have been incremented to their highest possible values for the bank note to be identified, the denomination count which is at least 28 and is at least 1.28 times larger than the next largest denomination count.

4. A method of identifying the denomination of a bank note or the like according to any one of the preceding claims wherein the comparison of the reflectance of light from each incremental area with that from each of a pre-selected number of other incremental areas taken in a preselected sequence and the production of the first correlation signal is carried out by producing a binary first correlation signal with a binary 1 for each comparison where the light reflected from the incremental area is larger than or equal that reflected from a previous incremental area and with a binary 0 for each comparison where the light reflected from the incremental area is less than the light reflected from a previous incremental area.

5. A method of identifying the denomination of a bank note or the like according to claim 4, wherein the said previous incremental areas are the second, fourth, sixth and eighth previous incremental areas.

6. Apparatus for identifying the denomination of a bank note comprising means to produce a signal p, whose magnitude is proportioned to the reflectance of light from an area of a bank note, means to store a representation for the reflectance of light from each of a plurality of different areas on the bank note, means to form a plurality of multi-bit correlation numbers N, where the first bit of each number is a one if Pn > Pn-2 but otherwise it is a zero, the second bit of each number is a one if Pn > PN-4 but otherwise the second bit is zero, the third bit of each number is a one if Pn > Pn-6 but otherwise the third bit is zero and the fourth bit of each number is a one if Pn > Pn-8 but otherwise the fourth bit is zero, where p, is the stored representation for the reflectance of light from a given area, Pn-2 is the stored representation for the reflectance of light from the second previous given area, Pn-4 is the stored representation for the reflectance from the fourth previous given area, Pn-6 is the stored representation for the reflectance from the sixth previous given area and Pn-8 is the stored representation for the reflectance from the eighth previous given area, means for comparing each said multi-bit correlation number n with a multi-bit number which corresponds to the same four-bit number derived from a sample note of each denomination of bank note detected by the apparatus and, on a favourable comparison, for incrementing a denomination count for the corresponding denomination, and means for producing an identity signal correlated to the identified denomination if the denomination count for such denomination is at least equal to 28 and is at least 1.28 times any other denomination count.

7. Apparatus according to claim 6 and also including means to direct light onto one side of the bank note to be identified and means to measure in sequence the reflected light from a plurality of incremental areas disposed across the side of the bank note.

8. Apparatus for identifying the denomination of a bank note or the like comprising means to direct light onto one side of the bank note to be identified, means to measure in sequence the reflected light from a plurality of incremental areas disposed across the side of the bank note, means for comparing the light reflected from each of the incremental areas with that from the second, fourth, sixth and eighth previous incremental area and producing a correlation number with a binary 1 for each comparison where the light reflected from the incremental area is larger than or equal to that reflected from a previous incremental area and with a binary 0 for each comparison where the light reflected from the incremental area is less than the light reflected from a previous incremental area, means for comparing each correlation number with a corresponding correlation number for each denomination identifiable by the apparatus, means for incrementing a denomination count when the produced correlation number corresponds to a corresponding correlation number and means for determining, after all denomination counts have been incremented to their highest possible value for the bank note to be identified, the denomination count which is at least 28 or at least 1.28 times larger than the next largest denomination count.

9. Apparatus according to claim 8 and also including means to output an indication of the denomination correlated to the denomination count that is at least 28 and at least 1.28 times larger than the next smallest denomination count.