Visualization pixel with Opencv Mat at

Question

I don't understand why output is a strange number when I run my code:

int main(int argc, char** argv)
{
    Mat im;
    im = imread("lena.png", CV_LOAD_IMAGE_GRAYSCALE);
    cout << im.at<uchar>(0, 0) << endl;
    waitKey(0);
}

If I visualize image I see the correct image. Where am I wrong?

Answer 1

Because it shows the symbol, like cout << char(123) << endl;

You have to use int cast:

cout << (int) im.at<uchar>(0, 0) << endl;

Answer 2

As stated in the official documentation you don´t get the actual intensity value directly but a scalar.

Try this:

Scalar intensity = im.at<uchar>(0, 0);

cout << intensity.val[0] << endl;

and for images with more than one channel you can use:

Vec3b intensity = im.at<Vec3b>(0, 0);
cout << intensity.val[0] << intensity.val[1] << intensity.val[2] << endl;