Tags: #notesonai
Topics: [[Computer Vision]]
---
# Scale-Invariant Feature Transform (SIFT)
SIFT is the solution to the question: Can we detect the same interest points regardless of image scale changes?
Basic idea:
- Divide the $16 \times 16$ window into a $4 \times 4$ grid of cells $(2 \times 2$ case shown below)
- Compute an orientation histogram for each cell (with 8 orientations)
- 16 cells (from $4 \times 4$ grids) \* 8 orientations (per cell) =128 dimensional descriptor
![[Sift-laplacian.jpg]]
Two popular scale invariant detectors:
![[sift-detectors.jpg]]
## Applications
Feature points are used for:
- Image alignment
- 3D reconstruction
- Motion tracking
- Robot navigation Indexing and database retrieval
- Object recognition
---
## References