vault backup: 2025-01-14 01:48:39

Biometric Systems/notes/11. Fingerprints.md

@@ -101,6 +101,8 @@ Once a fingerprint has been segmentated we can start extracting **macro-features
 
 ##### Directional map
 ~~The local orientation of the ridge line in the position [i, j] is defined as the angle $\theta(i,j)$ formed by considering the horizontal line at that point, and a point on the ridge line sufficiently closer to [i, j].~~
+
+Definizione: matrice in cui la cella [i, j] rappresenta l'angolo che la tangente alla ridge line forma con l'asse orizzontale.
 ![[Pasted image 20241127224325.png]]
 - most approaches use a grid measure (instead of measuring at each point)
 - the directional image D is a matrix in which each element denotes the average orientation of the ridge (of the tangent to the ridge) in a neighborhood of $[x_{i}, y_{i}]$