Studies were performed on a large number of diabetic patients with three levels of plantar sensation loss by analysing walking foot pressure images in the frequency domain. The feet of diabetic subjects were scanned over ten specified areas using Semmes-Weinstein's nylon monofilaments to determine quantitatively the three levels of neuropathy. A new parameter, the power ratio (PR, ratio of high frequency power to the total power in an image) was used to distinguish discretely between normal and diabetic feet in three levels of sensation loss. Analysis of results showed that the differences in PR values for diabetic feet (in all three levels of sensation loss) compared to normal feet were found to be highly significant (p<0.0005) in the areas of the foot where there was a high incidence of plantar ulcer formation, even at the early stage of neuropathy characterised by a sensation level of 45mN. This result could help in the early detection of plantar ulcer formation in the initial stage of sensation loss and may be utilised by orthopaedic surgeons to consider early corrective methods to protect these feet from further damage due to neuropathic ulcer formation.