Classification method and apparatus

1. A method of processing data derived from currency items, the method comprising:

measuring samples of currency items of classes to produce feature vectors in a first space; and

mapping the feature vectors to a second space in which there is a clearer separation of the classes than in the first space.

2. A method as claimed in claim 1 wherein the second space is determined using PCA or LDA.

3. A method as claimed in claim 2 wherein data in the first space is mapped to a third space using a non-linear mapping, and PCA or LDA is performed on the image of the data in the third space.

4. A method as claimed in claim 1 further comprising deriving a separating function separating the classes.

5. A method of classifying an item of currency comprising measuring the currency item to derive a feature vector and determining the class of the currency item using the result of a method as claimed in claim 1 .

6. A method of programming a currency validator comprising:

performing a method according to claim 1 using a plurality of samples of currency items; and

using a result from said performing to program the validator.

7. An apparatus for classifying items of currency comprising sensors to sense features of a currency item, a processor to generate a feature vector from the sensed values and a classifier to classify currency items using a result of a method as claimed in claim 1 .

8. An apparatus for classifying items of currency comprising a classifier to process feature vector data derived from currency items wherein the classification is equivalent to processing the input data, which is in a first space, in a second space where there is clearer separation of the classes than in the first space.

9. An apparatus as claimed in claim 8 wherein the second space is determined using PDA or LDA.

10. An apparatus as claimed in claim 8 wherein the second space is determined using PDA or LDA, in the image of the input space under a non-linear mapping.