Estimation of image feature orientation

ESTIMATION OF IMAGE FEATURE ORIENTATION 5 A method for estimating an orientation of an image feature located in an image region is disclosed. The method comprises the steps of: determining a plurality of gradient values from image pixels in the image region, wherein each gradient value is determined from a pair of differences located about a point, each difference being the difference between diagonally adjacent image pixels (410); calculating a double angle orientation representation for each of 3 the plurality of gradient values (450); processing the plurality of double angle gradient representations to generate smoothed double angle orientation representations (460); calculating at least one second order gradient value based on differences of the first order gradient values (420); and generating an estimate of an orientation of the image feature based on the at least one second order gradient value and the smoothed double angle orientation 5 representations (470, 480, 490). 2453699 1 IRN: 921372 400 Image Calculate first 410 order gradient vector field 430 Apply high pass filter Calculate second 420 Convert to order gradient 450 double angle vector field representation 435 460 Apply averaging 440 Combine 465 '\ 44 470 Generate energy operator 480 Correct rotation 485 Apply averaging filter 490 Orientation Fig. 4 vector field 2461010 IRN: 921372