%============================================s1.m=============================================
%Step1：Sobel算子求圖像梯度
%定義Sobel行算子和列算子
Hr = 0.25 * [-1 -2 -1;0 0 0;1 2 1];
Hc = 0.25 * [1 0 -1;2 0 -2;1 0 -1];

I = imread('pipe.jpg');     %將圖像讀入到I中
I = double(I);      %將I轉化為double型，方便卷積

%分別對圖像的RGB三個值求行梯度和列梯度
G_X_R = conv2(I(:,:,1),Hr);
G_Y_R = conv2(I(:,:,1),Hc);
G_X_G = conv2(I(:,:,2),Hr);
G_Y_G = conv2(I(:,:,2),Hc);
G_X_B = conv2(I(:,:,3),Hr);
G_Y_B = conv2(I(:,:,3),Hc);

%綜合6個分量計算圖像梯度
Gxx = G_X_R.^2 + G_X_G.^2 + G_X_B.^2;
Gyy = G_Y_R.^2 + G_Y_G.^2 + G_Y_B.^2;
Gxy = G_X_R.*G_Y_R + G_X_G.*G_Y_G + G_X_B.*G_Y_B;
theta = atan(2 * Gxy./(Gxx - Gyy)) / 2;
G = sqrt(abs(Gxx + Gyy + (Gxx - Gyy).*cos(2 * theta) + 2*Gxy.*sin(2 * theta)) / 2);

G = uint8(G);       %將G轉化為uint8型，方便輸出
%=========================================s1.m(end)==========================================