SIFT DESCRIPTOR

This descriptor is based on the gradient direction contribution of a neighborhood of the keypoint, SIFT descriptor is computed as follows

flowchart TD
A[select neighborhood of size 16x16]
B[split in regions of size 4x4]
C[compute gradient orientation histogram for each pixel]
A --> B --> C

The descriptor is given by all of the histogram of the regions so the dimension space of a SIFT descriptor is $R^{128}$

The gradient are rotated according to the canonical orientation of the gradient and each pixel is weighted by a Gaussian centered at the keypoint

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