change colour of canny output

edit

 # step 1: make a3 channel, bgr or rgb image from the canny output:
 edges = cv2.Canny(m,100,200)
 rgb = cv2.cvtColor(edges, cv2.COLOR_GRAY2RGB) # RGB for matplotlib, BGR for imshow() !

 # step 2: now all edges are white (255,255,255). to make it red, multiply with another array:
 rgb *= np.array((1,0,0),np.uint8) # set g and b to 0, leaves red :)

 # step 3: compose:
 out = np.bitwise_or(im2, rgb)

C++ implementation:

cv::Canny(im, edges, 100, 200);
// convert canny to BGR
cv::cvtColor(edges, edges, CV_GRAY2BGR); 
// multiply to make it red
red_canny = edges.mul(cv::Scalar(255, 0, 0), 1);