Patent ID: 8855443

Claim:
A method of detecting non-uniform spatial scaling of an image in a particular direction, the method comprising: dividing, by an active image process executing on a programmable apparatus, the image into regions; deriving for at least two of the regions a directional measure of spatial frequency energy in the particular direction; and comparing, by the programmable apparatus, said respective directional measures of spatial frequency energy in the particular direction for at least two of the regions to detect non-uniform spatial scaling in the particular direction; wherein a directional measure of total spatial frequency energy is evaluated in the particular direction for at least two of the regions and a measure of non-uniform spatial scaling is derived from a ratio of two said directional measures of total spatial frequency energy evaluated over two respective regions or groups of regions; where the particular direction is horizontal, the regions into which the image is divided comprise an image middle region and two image side regions respectively disposed on opposite horizontal sides of the image middle region and the ratio is the ratio of the horizontal directional measure of total spatial frequency energy evaluated over the image middle image region to the horizontal directional measure of total spatial frequency energy evaluated over the two image side regions.