[H, theta, rho] = hough(BW)[H, theta, rho] = hough(BW, ParameterName,ParameterValue)

peaks = houghpeaks(H, numpeaks)peaks = houghpeaks(..., param1, val1,param2, val2)

lines = houghlines(BW, theta, rho,peaks)lines = houghlines(..., param1, val1,param2, val2)

% 測試霍夫變換
clc
clear
close all 
% 讀取影象
I  = imread('circuit.tif');
rotI = imrotate(I,33,'crop'); % 旋轉33度，保持原圖片大小
fig1 = imshow(rotI);
% 提取邊
BW = edge(rotI,'canny');
figure, imshow(BW); 
% 霍夫變換
[H,theta,rho] = hough(BW); % 計算二值影象的標準霍夫變換，H為霍夫變換矩陣，theta,rho為計算霍夫變換的角度和半徑值
figure, imshow(imadjust(mat2gray(H)),[],'XData',theta,'YData',rho,...
    'InitialMagnification','fit');
xlabel('\theta (degrees)'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(hot) 
% 顯示霍夫變換矩陣中的極值點
P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:)))); % 從霍夫變換矩陣H中提取5個極值點
x = theta(P(:,2));
y = rho(P(:,1));
plot(x,y,'s','color','black'); 
% 找原圖中的線
lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);
figure, imshow(rotI), hold on
max_len = 0;
for k = 1:length(lines)
    % 繪製各條線
    xy = [lines(k).point1; lines(k).point2];
    plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');   
    % 繪製線的起點（黃色）、終點（紅色）
    plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
    plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');   
    % 計算線的長度，找最長線段
    len = norm(lines(k).point1 - lines(k).point2);
    if ( len > max_len)
        max_len = len;
        xy_long = xy;
    end
end
% 以紅色線高亮顯示最長的線
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','red');