1. Introduction
1. The essence of the SIFT algorithm is to find key points (feature points) in different scale spaces and calculate the direction of the key points. The key points found by SIFT are some very prominent points that will not change due to factors such as illumination, affine transformation and noise, such as corner points, edge points, bright points in dark areas, and dark points in bright areas.
a. Invariance: ——Invariance
to image rotation and scale changes; ——Strong
adaptability to three-dimensional viewing angle changes and illumination changes;
——Local features, which remain invariant when occlusion and scene clutter;
b. Strong discrimination : ——The
ability to distinguish between features is strong, which is conducive to matching;
c, the number is large:
——Lowe's original words: Generally 500*500 images can extract about 2000 feature points (this number depends on The choice of image content and several parameters).
Extract extreme points in the Difference of Gaussian (DOG) scale space and optimize them to obtain feature points.
2, the specific point detection step SIFT Algorithm:
- Construction of scale space;
- Difference of Gaussian scale space configuration;
--DoG point detecting scale-space extrema;
- precise positioning feature points;
- removing unstable points;
Second, the source code
close all;clear all;clc;
im1=imread('testdata\x1.jpg');
im2=imread('testdata\x2.jpg');
gray1=zoo_x2gray(im1);
gray2=zoo_x2gray(im2);
[des1,loc1]=zoo_sift(gray1);
[des2,loc2]=zoo_sift(gray2);
figure;zoo_drawPoints(im1,loc1,im2,loc2);
Num=3;
Thresh=0.85;
match=zoo_BidirectionalMatch(des1,des2,Num,Thresh);
clear des1 des2
loc1=loc1(match(:,1),:);
loc2=loc2(match(:,2),:);
figure;zoo_linePoints(im1,loc1,im2,loc2);
agl=zoo_getRotAgl(loc1,loc2);
figure;zoo_drawRotAglHist(agl);
opt=zoo_optIndex(agl);
loc1=loc1(opt,:);
loc2=loc2(opt,:);
figure;zoo_linePoints(im1,loc1,im2,loc2);
T=zoo_getTransMat(gray1,loc1,gray2,loc2);
im=zoo_imRegist(im1,im2,T);
figure,imshow(im);
Three, running results
Four, remarks
Complete code or writing add QQ2449341593 past review
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