How to realize the callback function of OpenCV4.X mouse
In this issue, the editor will bring you about how to achieve the OpenCV4.X mouse callback function. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.
1. Callback function
SetMouseCallback (windowName, onMouse, param=None)
WindowName: window name
OnMouse: mouse response handling function
Mouse callback function, which is called when a mouse event occurs. The mouse event can be any action related to the mouse, such as left button down, left button up, left button double click, etc. It provides us with the coordinates of each mouse event (xmemy). Through this event and location, we can do whatever we want. All mouse events can be listed with the following code.
"Code"
Import cv2
Events = [i for i in dir (cv2) if 'EVENT' in I]
Print (events)
"output"
['EVENT_FLAG_ALTKEY',' EVENT_FLAG_CTRLKEY', 'EVENT_FLAG_LBUTTON'
'EVENT_FLAG_MBUTTON', 'EVENT_FLAG_RBUTTON',' EVENT_FLAG_SHIFTKEY'
'EVENT_LBUTTONDBLCLK', 'EVENT_LBUTTONDOWN',' EVENT_LBUTTONUP', 'EVENT_MBUTTONDBLCLK'
'EVENT_MBUTTONDOWN', 'EVENT_MBUTTONUP',' EVENT_MOUSEHWHEEL', 'EVENT_MOUSEMOVE'
'EVENT_MOUSEWHEEL', 'EVENT_RBUTTONDBLCLK',' EVENT_RBUTTONDOWN', 'EVENT_RBUTTONUP']
Parameter meaning
EVENT_MOUSEMOVE 0 slide
EVENT_LBUTTONDOWN 1 left click
EVENT_RBUTTONDOWN 2 right click
EVENT_MBUTTONDOWN 3 Middle Click
EVENT_LBUTTONUP 4 left button release
EVENT_RBUTTONUP 5 right-click release
EVENT_MBUTTONUP 6 Intermediate release
EVENT_LBUTTONDBLCLK 7 left double click
EVENT_RBUTTONDBLCLK 8 right double click
EVENT_MBUTTONDBLCLK 9 double click in the middle
Second, application 1. Application one
Create a simple application that can draw a circle on the image as long as we double-click it.
"Code"
Import numpy as np
Import cv2
# mouse callback function
Def draw_circle (event, x, y, flags, param):
If event = = cv2.EVENT_LBUTTONDBLCLK:
Cv2.circle (img, (x, y), 100,255,0,0),-1)
# Create a black image, a window and bind the function to window
Img = np.zeros ((512,512,3), np.uint8)
Cv2.namedWindow ('image')
Cv2.setMouseCallback ('image', draw_circle)
While True:
Cv2.imshow ('image', img)
If cv2.waitKey (20) & 0xFF = = 27:
Break
Cv2.destroyAllWindows ()
two。 Application two
Draw a rectangle or circle by dragging the mouse (depending on the mode we choose), just like in a drawing application. So our mouse callback function has two parts, one for drawing rectangles and the other for drawing circles. In the main loop, set the key'm'to set the keyboard binding to switch between rectangles and circles.
"Code"
Import numpy as np
Import cv2
Drawing = False # true if mouse is pressed
Mode = True # if True, draw rectangle. Press 'm'to toggle to curve
Ix,iy =-1mai Mui 1
# mouse callback function
Import numpy as np
Import cv2
Drawing = False # true if mouse is pressed
Mode = True # if True, draw rectangle. Press 'm'to toggle to curve
Ix,iy =-1mai Mui 1
# mouse callback function
Def draw_circle (event,x,y,flags,param):
Global ix,iy,drawing,mode
If event = = cv2.EVENT_LBUTTONDOWN:
Drawing = True
Ix,iy = XBI y
Elif event = = cv2.EVENT_MOUSEMOVE:
If drawing = = True:
If mode = = True:
Cv2.rectangle (img, (ix,iy), (xmemy), (0pr 255pr 0),-1)
Else:
Cv2.circle (img, (xQuery), 5, (0B0255),-1)
Elif event = = cv2.EVENT_LBUTTONUP:
Drawing = False
If mode = = True:
Cv2.rectangle (img, (ix,iy), (xmemy), (0pr 255pr 0),-1)
Else:
Cv2.circle (img, (xQuery), 5, (0B0255),-1)
Img = np.zeros ((512, 512), np.uint8)
Cv2.namedWindow ('image')
Cv2.setMouseCallback ('image',draw_circle)
While True:
Cv2.imshow ('image',img)
K = cv2.waitKey (1) & 0xFF
If k = = ord ('m'):
Mode = not mode
Elif k = = 27:
Break
Cv2.destroyAllWindows ()
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