I am working through the book "Learning OpenCV" from the O'Reilly series and am trying to perform a canny edge detection sample. Any grayscale image I choose seems to come up as having 3 channels, and to the best of my knowledge, canny only works with single channel images, so this always fails. I am even using the images provided by OpenCV. Here is my code.. IplImage* doCanny(IplImage* in, double lowThresh, double highThresh, double aperture) { if(in->nChannels != 1) return(0); //canny only handles gray scale images IplImage* out = cvCreateImage(cvSize(in->width, in->height), IPL_DEPTH_8U, 1); cvCanny(in, out, lowThresh, highThresh, aperture); return(out); }; IplImage* img = cvLoadImage("someGrayscaleImage.jpg"); IplImage* out = doCanny(img, 10, 100, 3); Why might this always give me 3-channel images? How can I solve this?