Abigail asked . 2023-02-09

Error in my edge detection function?

I'm attempting to create a canny edge detector and I've run into a speed bump while checking for the edge pixels. Below I have the code I'm using to check which pixel is on an edge but I keep getting the error "Attempted to access mag(0,18); index must be a positive integer or logical" Is there a way to fix this? For this code, mag=gradient magnitude, dir=gradient direction, img=image, and edgecand=the edge candidate.

edgecand = mag;
for x=1:size(img,1);
    for y=1:size(img,2);
        if (dir(x,y)==1);
            if(mag(x,y)>mag(x-1,y))&&(mag(x,y)>mag(x+1,y));
                %happy
            else edgecand(x,y)=0;
            end
        end
        if (dir(x,y)==2);
            if(mag(x,y)<mag(x+1,y+1))&&(mag(x,y)>mag(x-1,y-1));
                %happy
            else edgecand(x,y)=0;
            end
        end
        if (dir(x,y)==3);
            if(mag(x,y)>mag(x,y-1))&&(mag(x,y)<mag(x,y+1));
                %happy
            else edgecand(x,y)=0;
            end
        end
        if (dir(x,y)==4);
            if(mag(x,y)>mag(x+1,y-1))&&(mag(x,y)<mag(x-1,y+1));
                %happy
            else edgecand(x,y)=0;
            end
        end
    end
end

detection , image processing , edge candidates , Image Processing and Computer Vision , Image Segm