Seriously Abdelrahiem,

bw1 = edge(I,'Canny'); will work

I assume that the canny edge is working well but you are surprised by the outcome...

While sobel and prewitt remain in the greyscale (or even color) space, canny tends to present the results binary (aka b/w). Though this is not a precondition.

Regards

Excuse  me Aparna Murthy, the command do not work, I use MatLab R2013a

Hello Sir,

       Still I am working with Matlab 2012R, edge function will perfectly work. But see the arguement image I should be in grayscale form , if it is RGB from error will come. I am sure you tried with colour image, you convert the image first in grayscale then you try.

Eg:- 

     I=imread('cameraman.tif');

     E=edge(I,'canny');

    figure;imshow(E,[]);title('canny edge output');

(The above code worked perfectly)

YOU PLS TRY 

I=rgb2gray(imread('imagename.tif'));

E=edge(I,'canny');

figure;imshow(E,[]);title('canny edge output');

surely it will work.

Hope it's clear.

Thank you much my colleague Manikandan Vm, but I repeat this code many times after I convert image to grayscale. Error still founded.

Also, if the image was binary format, is the function edge works or not?

Hello Sir,

      If you don't mind please share the the ERROR DESCRIPTION....we will fix it.... you pls see the attached screen shot...shows how the result will be....when I tried with edge function.

Surely it will work for an input in binary form..... But edges might vary when you consider binary image instead of gray scale image. But surely you will get the result without any error.

@Abdelrahiem Ahmed Hashem: I too agree to all ..there is absolutely no reason for canny to not work if sobel and prewitt work in your system (I mean by chance if the edge code is not corrupt or overwritten in your system).. Would u mind sharing the error plz?

That is funny !!!!!!! I work with all the time , I use 2016 that should not be a problem !!!

Check -Image data type (unit8,16...)  , rgb2gray (...) should do as Manikandan has used it returns uint8.

Check the array (2D) for its dimensions (color-MxNx3) and then gray- MxN (uint8)

Worst case: take a gray image and use the same operator.

I =imread('train3.jpg');

imshow(I)

I=rgb2gray(I);

figure,imshow(I);

BW1 = edge(I,'sobel');

figure,imshow(BW1);

BW3 = edge(I,'canny');

figure,imshow(BW3);

%figure;

imshowpair(BW1,BW3,'montage')

title('Sobel Filter Canny Filter');

Try adding just edge functionality on the code initially, then go with the respective methods

Error in edge

BW1 = edge(I,'Canny'); for the code

I = imread('circuit.tif');

imshow(I);

BW1 = edge(I,'Canny');