OpenCV binary image get only white pixels don't work

Question

I'm doing some image processing to learn, I'm using openCV with the new C++ iterface.

I have an RGB image, I read the grayscale version, equalize the histogram, then use canny to detect edges.

The question is: does the Canny function return a grayscale image or a binary one? I use a double for loop to check the values of pixels in the image resulting of applying canny edge detector, and I have a lot of values totally different. In a binary image must be only two values 0 or 1 (0 or 255)... How can I do that?

My code:

imagen = imread(nombre_imagen,0); //lee la imagen en escala de grises
equalizeHist(imagen,imagen);
Canny(binary,binary,0.66*threshold,1.33*threshold,3,true);
for(int i=0;i<binary.rows;i++){
    for(int j=0;j<binary.cols;j++){
       std::cout << binary.at<float>(i,j)<< ",";
    }
    std::cout << "\n";
}

This is a 183x183 matrix and I can see a lot of values even some nan. How can I make this binary?

For the Canny function I use a threshold value obtaining the "mean" value of the grayscale image; I saw it here: http://www.kerrywong.com/2009/05/07/canny-edge-detection-auto-thresholding/.

David Titarenco David Titarenco · Accepted Answer · 2011-04-28T07:44:39

Binary images have type uchar which you need to cast to int (or unsigned int) if you want the 0-255 range:

for(int i=0;i<edges.rows;i++) {
    for(int j=0;j<edges.cols;j++) {
       std::cout << (int)edges.at<uchar>(i,j)<< ",";
    }
    std::cout << "\n";
}

You should avoid the C-style cast, but I'll leave that as an exercise to the reader.

OpenCV binary image get only white pixels don't work

2 Answers