Peak determination in two-dimensional optical spectra

A method of determining a peak intensity in an optical spectrum comprises producing a two- dimensional array (20) of spectrum values by imaging the optical spectrum onto a detector array (13); selecting a first two-dimensional subarray (21) of the array of spectrum values such that the subarray includes a first peak (1) of the spectrum, the first peak having an expected location; interpolating, within the first subarray (21), the spectrum values to produce a first interpolated subarray; determining, by using the first interpolated subarray, an actual location of the first peak (1); determining an offset by using the actual location and the expected location of the first peak; adjusting an expected location of a second peak (2) of the spectrum by using the offset; selecting a second two-dimensional subarray (22) of the array of spectrum values such that the second subarray includes the second peak (2), the second peak having an adjusted expected location; and using, within the second subarray (22), interpolated spectrum values to produce a peak intensity value of the second peak.