## 霍夫变换

Image Processing Toolbox™ 支持使您能够使用霍夫变换检测图像中线条的函数。

hough 函数实现标准霍夫变换 (SHT)。霍夫变换设计为使用线条的参数化表示来检测线条：

rho = x*cos(theta) + y*sin(theta)

### 使用霍夫变换检测图像中的线条

I = imread('circuit.tif'); rotI = imrotate(I,33,'crop'); imshow(rotI)

BW = edge(rotI,'canny'); imshow(BW);

[H,theta,rho] = hough(BW);

figure imshow(imadjust(rescale(H)),[],... 'XData',theta,... 'YData',rho,... 'InitialMagnification','fit'); xlabel('\theta (degrees)') ylabel('\rho') axis on axis normal hold on colormap(gca,hot)

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));

x = theta(P(:,2)); y = rho(P(:,1)); plot(x,y,'s','color','black');

lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);

figure, imshow(rotI), hold on max_len = 0; for k = 1:length(lines) xy = [lines(k).point1; lines(k).point2]; plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green'); % Plot beginnings and ends of lines plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow'); plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red'); % Determine the endpoints of the longest line segment len = norm(lines(k).point1 - lines(k).point2); if ( len > max_len) max_len = len; xy_long = xy; end end % highlight the longest line segment plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','red');