OpenCV: Drawing on an image

Question

I am working on a program using the OpenCV library (though I am quite a noob on it). One of the things I need to do is to draw on the image. I looked at the OpenCV drawing functions and they all seem pretty simple (Circle, Line, etc), however the program won't compile! It says this to be exact: error C3861: 'Line': identifier not found. Is there something I haven't installed? I used the tutorial on http://opencv.willowgarage.com/wiki/VisualC%2B%2B_VS2008 to install OpenCV on Visual Studio 2008 and so far this is the only real problem I have. Please help me! I need this program working as soon as possible!

score 4 · Answer 1 · answered Aug 25 '10 at 10:52

4

The function to draw a line in the OpenCV C API is named cvLine, not Line.

answered Aug 25 '10 at 10:52

Phil Ross

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Ok... That was easy. Nothing was said in the site -_- http://opencv.willowgarage.com/documentation/python/drawing_functions.html Thank you very much! – Juls Aug 25 '10 at 11:46
@Juls The link you posted is for the Python documentation, which is why the function names are different. – Phil Ross Aug 25 '10 at 12:12
1

+1 Accurate. Juls, don't forget to vote up on his answer or accept it as the official solution. – karlphillip Aug 25 '10 at 13:27

score 1 · Answer 2 · answered Nov 01 '12 at 22:09

I think you have fallen victim of the following common mistake: C includes are in #include <opencv/core.h> etc, whereas C++ includes are:

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <oppencv2/highgui/highgui.hpp>

Include these for drawing and showing the image. Use using namespace cv; then you don't have to write cv::line just line and everything will be working fine.
I had to battle with the very same problem when I began. ;)

(And btw use cv::Mat for c++.)

score 0 · Answer 3 · answered Jan 15 '18 at 06:09

You can now easily paint on OpenCV images. For this you need to call the setMouseCallback(‘window_name’,image_name) function on opencv. After that you can easily handle the Mouse Callback Function upon your images. Then you need to detect the cv2.EVENT_LBUTTONDOWN, cv2.EVENT_MOUSEMOVE and cv2.EVENT_LBUTTONUP events. By checking the proper boolean condition you need to decide how you like to interact with the OpenCV images.

def paint_draw(event,former_x,former_y,flags,param):
    global current_former_x,current_former_y,drawing, mode

    if event==cv2.EVENT_LBUTTONDOWN:
        drawing=True
        current_former_x,current_former_y=former_x,former_y

    elif event==cv2.EVENT_MOUSEMOVE:
        if drawing==True:
            if mode==True:
                cv2.line(image,(current_former_x,current_former_y),(former_x,former_y),(0,0,255),5)
                current_former_x = former_x
                current_former_y = former_y
    elif event==cv2.EVENT_LBUTTONUP:
        drawing=False
        if mode==True:
            cv2.line(image,(current_former_x,current_former_y),(former_x,former_y),(0,0,255),5)
            current_former_x = former_x
            current_former_y = former_y
    return former_x,former_y

For details you can see link: How to Paint on OpenCV Images and Save the Image

Output:

OpenCV: Drawing on an image

3 Answers3