changed default parameters of SURF, which improved its performance. Restored bi-linear interpolation in SURF descriptor extractor. Added test for SURF homography + check for non-zero (positive) responses.

modified SIFT to 1) double image before finding keypoints, 2) use floating-point internally instead of 16-bit integers, 3) set the keypoint response to the abs(interpolated_DoG_value). step 1) increases the number of detected keypoints significantly and together with 2) and 3) it improves some detection benchmarks. On the other hand, the stability of the small keypoints is lower, so the rotation and scale invariance tests now struggle a bit. In 2.5 need to make this feature optional and add some more intelligence to the algorithm.

added test that finds a planar object using SIFT.

It calcs kpts for a cross and checks that 4 kpts at the edges have equal responce.