newharris.m

harris角点检测功能

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%   Harris角点提取算法：首先求自相关矩阵的四个元素，然后利用det(M)-0.06*(trace(M))^2这个判别式对每个像素进行计算，求出该判别式的最大值。将图像中的每个像素点与阈值0.01*判别式最大值进行比较，并与像素周围的八个像素点进行比较，若为极值，则为角点                                       % 
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clear; 
filename='E:\work\Harris\smallima1.bmp'; 
X= imread(filename);% 读取图像

Info=imfinfo(filename); %将彩色图像转化成灰度图像
if Info.BitDepth>8 
    f=rgb2gray(X); 
end 
% 
% fx = [5 0 -5;8 0 -8;5 0 -5];          % 高斯函数一阶微分，x方向(用于改进的Harris角点提取算法) 
ori_im=double(f)/255;                   %unit8转化为64为双精度double64 
fx = [-2 -1 0 1 2];                     % x方向梯度算子(用于Harris角点提取算法) 
Ix = filter2(fx,ori_im);                % x方向滤波 ，得到一个干净清晰的图像
% fy = [5 8 5;0 0 0;-5 -8 -5];          % 高斯函数一阶微分，y方向(用于改进的Harris角点提取算法) 
fy = [-2;-1;0;1;2];                     % y方向梯度算子(用于Harris角点提取算法) 
Iy = filter2(fy,ori_im);                % y方向滤波 
Ix2 = Ix.^2; 
Iy2 = Iy.^2; 
Ixy = Ix.*Iy; 
clear Ix; 
clear Iy; 
 
h= fspecial('gaussian',[7 7],2);        % 产生7*7的高斯窗函数，sigma=2 
 
Ix2 = filter2(h,Ix2); 
Iy2 = filter2(h,Iy2); 
Ixy = filter2(h,Ixy); 
 
height = size(ori_im,1); %返回图像行数
width = size(ori_im,2); %返回图像列数
result = zeros(height,width);           % 纪录角点位置，角点处值为1 
 
R = zeros(height,width); 
 
Rmax = 0;                              % 图像中最大的R值 
for i = 1:height 
    for j = 1:width 
        M = [Ix2(i,j) Ixy(i,j);Ixy(i,j) Iy2(i,j)];             % auto correlation matrix 
        R(i,j) = det(M)-0.06*(trace(M))^2;                     % 计算R 
        if R(i,j) > Rmax 
            Rmax = R(i,j); 
        end; 
    end; 
end; 
 
cnt = 0; 
for i = 2:height-1 
    for j = 2:width-1 
        % 进行非极大抑制，窗口大小3*3 
        if R(i,j) > 0.01*Rmax && R(i,j) > R(i-1,j-1) && R(i,j) > R(i-1,j) && R(i,j) > R(i-1,j+1) && R(i,j) > R(i,j-1) && R(i,j) > R(i,j+1) && R(i,j) > R(i+1,j-1) && R(i,j) > R(i+1,j) && R(i,j) > R(i+1,j+1) 
            result(i,j) = 1; 
            cnt = cnt+1; 
        end; 
    end; 
end; 
 
[posc, posr] = find(result == 1); 
cnt                                      % 角点个数 
imshow(ori_im);
title('Harris Corner')

hold on; 
plot(posr,posc,'r+');