Michael Vanegas asked . 2023-02-08

Imshow and Imshowpair differences?

q = imread('circuit.tif');

%% STEP1: Apply Gaussian Filter
q_output1 = imgaussfilt(q,1.5);

%JUST FOR FUN, I AM PERFORMING BOTH PREWITT AND SOBEL TO PERFORM THE CANNY
Canny_Prewitt_KernalX = [-1 0 1;-1 0 1;-1 0 1];
Canny_Prewitt_KernalY = Canny_Prewitt_KernalX';
Canny_Sobel_KernalX = [-1 0 1;-2 0 2;-1 0 1];
Canny_Sobel_KernalY = -Canny_Sobel_KernalX';

% STEP2: GRADIENT CALCULATION
Canny_Prewitt_FiltX = filter2(Canny_Prewitt_KernalX,q_output1,'same'); % Gx
Canny_Prewitt_FiltY = filter2(Canny_Prewitt_KernalY,q_output1,'same'); % Gy
Canny_Prewitt_Edge = sqrt(Canny_Prewitt_FiltX.^2 + Canny_Prewitt_FiltY.^2); % V - Gradient Intensity Matrix

Canny_Sobel_FiltX = filter2(Canny_Sobel_KernalX,q_output1,'same'); % Gx
Canny_Sobel_FiltY = filter2(Canny_Sobel_KernalY,q_output1,'same'); % Gy
Canny_Sobel_Edge = sqrt(Canny_Sobel_FiltX.^2 + Canny_Sobel_FiltY.^2); % V - Gradient Intensity Matrix

Canny_Prewitt_Theta = atan2(Canny_Prewitt_FiltY,Canny_Prewitt_FiltX).*(180/pi); % Theta
Canny_Sobel_Theta = atan2(Canny_Sobel_FiltY,Canny_Sobel_FiltX).*(180/pi); % Theta

% The theta areas contain NaN values so lets replace them with 0.
Canny_Prewitt_Theta(isnan(Canny_Prewitt_Theta)) = 0;
Canny_Sobel_Theta(isnan(Canny_Sobel_Theta)) = 0;

% To correct for same angles in the negative just add 360 to any value less than 0
rows = size(Canny_Prewitt_Theta,1);
columns = size(Canny_Sobel_Theta,2);

for i = 1:rows    % THIS FOR LOOP TURNS -ANGLES TO A RANGE OF 0-180!
    for j = 1:columns
        if Canny_Prewitt_Theta(i,j) < 0 
            Canny_Prewitt_Theta(i,j) = Canny_Prewitt_Theta(i,j) + 180;
            
        elseif Canny_Sobel_Theta(i,j) < 0
            Canny_Sobel_Theta(i,j) = Canny_Sobel_Theta(i,j) +180;

        elseif Canny_Prewitt_Theta(i,j) < 0 && Canny_Sobel_Theta(i,j) < 0
            Canny_Prewitt_Theta(i,j) = Canny_Prewitt_Theta(i,j) + 180;
            Canny_Sobel_Theta(i,j) = Canny_Sobel_Theta(i,j) +180;
        end
    end
end
    
Canny_BW_Prewitt_Edge = imbinarize(Canny_Prewitt_Edge/255,0.3);
Canny_BW_Sobel_Edge = imbinarize(Canny_Sobel_Edge/255,0.3);

% STEP3: NON-MAXIMUM SUPRESSION

rows = size(Canny_Prewitt_Theta,1);
columns = size(Canny_Sobel_Theta,2);

% THESE FOR LOOPS FORM THE LOGIC FOR THE IMAGE NON-MAX SUPRESSION TEST
for i = 2:rows-1
    for j = 2:columns-1
        
        Prewitt_Result = [1 2 3 4 5].*...
               [Canny_Prewitt_Theta(i,j) < 22.5,...
                Canny_Prewitt_Theta(i,j) >= 22.5 && Canny_Prewitt_Theta(i,j) < 67.5,...
                Canny_Prewitt_Theta(i,j) >= 67.5 && Canny_Prewitt_Theta(i,j) < 112.5,...
                Canny_Prewitt_Theta(i,j) >= 112.5 && Canny_Prewitt_Theta(i,j) < 157.5,...
                Canny_Prewitt_Theta(i,j) >= 157.5 && Canny_Prewitt_Theta(i,j) <= 180];

            switch Prewitt_Result(Prewitt_Result~=0)
                case 1 
                    if Canny_Prewitt_Edge(i,j-1) > Canny_Prewitt_Edge(i,j) 
                       Canny_Prewitt_Edge(i,j) = 0;
                    elseif Canny_Prewitt_Edge(i,j+1) > Canny_Prewitt_Edge(i,j)
                       Canny_Prewitt_Edge(i,j) = 0;
                    end
                    
                case 2 
                    if Canny_Prewitt_Edge(i-1,j+1) > Canny_Prewitt_Edge(i,j) 
                       Canny_Prewitt_Edge(i,j) = 0;
                    elseif Canny_Prewitt_Edge(i+1,j-1) > Canny_Prewitt_Edge(i,j)
                       Canny_Prewitt_Edge(i,j) = 0;
                    end  
                    
                case 3 
                    if Canny_Prewitt_Edge(i-1,j) > Canny_Prewitt_Edge(i,j) 
                       Canny_Prewitt_Edge(i,j) = 0;
                    elseif Canny_Prewitt_Edge(i+1,j) > Canny_Prewitt_Edge(i,j)
                       Canny_Prewitt_Edge(i,j) = 0;
                    end 
                case 4 
                    if Canny_Prewitt_Edge(i-1,j-1) > Canny_Prewitt_Edge(i,j) 
                       Canny_Prewitt_Edge(i,j) = 0;
                    elseif Canny_Prewitt_Edge(i+1,j+1) > Canny_Prewitt_Edge(i,j)
                       Canny_Prewitt_Edge(i,j) = 0;
                    end 
                case 5
                    if Canny_Prewitt_Edge(i,j-1) > Canny_Prewitt_Edge(i,j) 
                       Canny_Prewitt_Edge(i,j) = 0;
                    elseif Canny_Prewitt_Edge(i,j+1) > Canny_Prewitt_Edge(i,j)
                       Canny_Prewitt_Edge(i,j) = 0;
                    end 
            end
                    
        Sobel_Result = [1 2 3 4 5].*...
                       [Canny_Sobel_Theta(i,j) < 22.5,...
                        Canny_Sobel_Theta(i,j) >= 22.5 && Canny_Sobel_Theta(i,j) < 67.5,...
                        Canny_Sobel_Theta(i,j) >= 67.5 && Canny_Sobel_Theta(i,j) < 112.5,...
                        Canny_Sobel_Theta(i,j) >= 112.5 && Canny_Sobel_Theta(i,j) < 157.5,...
                        Canny_Sobel_Theta(i,j) >= 157.5 && Canny_Sobel_Theta(i,j) <= 180];   
                    
            switch Sobel_Result(Sobel_Result~=0)
                case 1 
                    if Canny_Sobel_Edge(i,j-1) > Canny_Sobel_Edge(i,j) 
                       Canny_Sobel_Edge(i,j) = 0;
                    elseif Canny_Sobel_Edge(i,j+1) > Canny_Sobel_Edge(i,j)
                       Canny_Sobel_Edge(i,j) = 0;
                    end
                    
                case 2 
                    if Canny_Sobel_Edge(i-1,j+1) > Canny_Sobel_Edge(i,j) 
                       Canny_Sobel_Edge(i,j) = 0;
                    elseif Canny_Sobel_Edge(i+1,j-1) > Canny_Sobel_Edge(i,j)
                       Canny_Sobel_Edge(i,j) = 0;
                    end  
                    
                case 3 
                    if Canny_Sobel_Edge(i-1,j) > Canny_Sobel_Edge(i,j) 
                       Canny_Sobel_Edge(i,j) = 0;
                    elseif Canny_Sobel_Edge(i+1,j) > Canny_Sobel_Edge(i,j)
                       Canny_Sobel_Edge(i,j) = 0;
                    end 
                case 4 
                    if Canny_Sobel_Edge(i-1,j-1) > Canny_Sobel_Edge(i,j) 
                       Canny_Sobel_Edge(i,j) = 0;
                    elseif Canny_Sobel_Edge(i+1,j+1) > Canny_Sobel_Edge(i,j)
                       Canny_Sobel_Edge(i,j) = 0;
                    end 
                case 5
                    if Canny_Sobel_Edge(i,j-1) > Canny_Sobel_Edge(i,j) 
                       Canny_Sobel_Edge(i,j) = 0;
                    elseif Canny_Sobel_Edge(i,j+1) > Canny_Sobel_Edge(i,j)
                       Canny_Sobel_Edge(i,j) = 0;
                    end 
            end
                      
    end
end

% Image borders cannot be traversed by the FOR Loop, so set to 0! 
% WARNING!! THIS CAUSES SOME ISSUES CHECK AGAIN AFTER FINISHING
Canny_Prewitt_Edge(1,:) = 0;
Canny_Prewitt_Edge(max(rows),:) = 0;
Canny_Prewitt_Edge(:,1) = 0;
Canny_Prewitt_Edge(:,max(columns)) = 0;

Canny_Sobel_Edge(1,:) = 0;
Canny_Sobel_Edge(max(rows),:) = 0;
Canny_Sobel_Edge(:,1) = 0;
Canny_Sobel_Edge(:,max(columns)) = 0;

figure(34)
imshowpair(Canny_Prewitt_Edge,Canny_Sobel_Edge,'montage','Scaling','none');title('Non-Max Suppression');

figure(35)
subplot(121),imshow(Canny_Prewitt_Edge,colormap('gray'));shtitle('Non-Max Suppression');title('Canny using Prewitt');
subplot(122),imshow(Canny_Sobel_Edge,colormap('gray'));title('Canny using Sobel');

image processing , edge detection , Image Processing and Computer Vision