Training of SVM classifier using SIFT features

Question

please i like to classify a set of image in 4 class with SIFT DESCRIPTOR and SVM. Now, using SIFT extractor I get keypoints of different sizes exemple img1 have 100 keypoin

Answer 1

You will always get different number of keypoints for different images, but the size of feature vector of each descriptor point remains same i.e. 128. People prefer using Vector Quantization or K-Mean Clustering and build Bag-of-Words model histogram. You can have a look at this thread.