Opencv mouse event + interface interaction drawing rectangle polygon selection ROI

1.Opencv Mouse events

import cv2

d=[i for i in dir(cv2) if 'EVENT' in i]
print(d)

'EVENT_FLAG_ALTKEY'： Represents drag and drop events . Hold down alt Key not put 
'EVENT_FLAG_CTRLKEY' Hold down ctrl Key not put 
'EVENT_FLAG_LBUTTON' Hold down the left button and drag 
'EVENT_FLAG_MBUTTON' Middle drag 
'EVENT_FLAG_RBUTTON' Right click and drag 
'EVENT_FLAG_SHIFTKEY' Hold down shift Don't put 
'EVENT_LBUTTONDBLCLK'event Mouse events . Next, double-left click on 
'EVENT_LBUTTONDOWN' Press the left key 
'EVENT_LBUTTONUP' Release left key 
 'EVENT_MBUTTONDBLCLK'  Double-click the key 
 'EVENT_MBUTTONDOWN' Middle click 
 'EVENT_MBUTTONUP' Middle key release 
 'EVENT_MOUSEHWHEEL'
 'EVENT_MOUSEMOVE' slide 
 'EVENT_MOUSEWHEEL',
 'EVENT_RBUTTONDBLCLK', Right click double-click 
 'EVENT_RBUTTONDOWN', Right click on the 
 'EVENT_RBUTTONUP' Right click to release 

The callback function uses ：

cv2.setMousecallback(const string& winname, MouseCallback onMouse, void* userdata=0）

winname: The name of the window  
onMouse: Mouse response function , Callback function . Specifies when each mouse time occurs in the window , Pointer to the called function .  The prototype of this function should be void on_Mouse(int event, int x, int y, int flags, void* param);
userdate： Parameters passed to the callback function  

Response function use ：

void on_Mouse(int event, int x, int y, int flags, void* param);
event yes  CV_EVENT_* One of the variables 
x and y It's the coordinates of the mouse pointer in the image coordinate system （ It's not a window coordinate system ） 
flags yes CV_EVENT_FLAG The combination of , param It's user-defined and passed to setMouseCallback The parameters of the function call .

2. Draw a rectangle ROI

2.1 Method 1

import cv2

global img
global point1, point2

# Mouse response function 
def Rectangular_box(event, x, y, flags, param):
    global img, point1, point2
    img2 = img.copy()
    if event == cv2.EVENT_LBUTTONDOWN:  #  Left click 
        point1 = (x, y)
        cv2.circle(img2, point1, 10, (0, 255, 0), 5)
        cv2.imshow('img', img2)
    elif event == cv2.EVENT_MOUSEMOVE and (flags & cv2.EVENT_FLAG_LBUTTON):  #  Press and hold the left button to drag 
        cv2.rectangle(img2, point1, (x, y), (255, 0, 0), 5)
        cv2.imshow('img', img2)
    elif event == cv2.EVENT_LBUTTONUP:  #  Left release 
        point2 = (x, y)
        cv2.rectangle(img2, point1, point2, (0, 255, 255), 4)
        cv2.imshow('img', img2)
        min_x = min(point1[0], point2[0])
        min_y = min(point1[1], point2[1])
        width = abs(point1[0] - point2[0])
        height = abs(point1[1] - point2[1])
        cut_img = img[min_y:min_y + height, min_x:min_x + width]
        #cv2.imwrite('baocun.jpg', cut_img)
        cv2.imshow('result',cut_img
def main():
    global img
    img = cv2.imread('yangmi.jpg')
    img=cv2.resize(img,None,fx=0.4,fy=0.4)
    cv2.namedWindow('image')
    cv2.setMouseCallback('image', Rectangular_box)
    cv2.imshow('image', img)
    cv2.waitKey(0)
if __name__ == '__main__':
    main()

2.2 Method 2

import cv2
import imutils
 
img = cv2.imread("./test_image.jpg")
img = imutils.resize(img, width=500)
 
roi = cv2.selectROI(windowName="roi", img=img, showCrosshair=True, fromCenter=False)
x, y, w, h = roi
 
cv2.rectangle(img=img, pt1=(x, y), pt2=(x + w, y + h), color=(0, 0, 255), thickness=2)
cv2.imshow("roi", img)
cv2.waitKey(0)
cv2.destroyAllWindows()

3. Draw polygon ROI

polygon ROI, It mainly uses mouse interaction to draw ：

1. Left click , Select the points of the polygon ;
2. Right click , Delete the most recent selection ;
3. Middle click , determine ROI Area and visualize .
4. Press ”S“ key , Put the polygon ROI Save the points of the area to the local ”config.pkl" In file .

import cv2
import imutils
import numpy as np
import joblib
 
pts = []  #  For storage point 
 
 
#  A unified ：mouse callback function
def draw_roi(event, x, y, flags, param):
    img2 = img.copy()
 
    if event == cv2.EVENT_LBUTTONDOWN:  #  Left click , Select point 
        pts.append((x, y))  
 
    if event == cv2.EVENT_RBUTTONDOWN:  #  Right click on the , Cancel the last selected point 
        pts.pop()  
 
    if event == cv2.EVENT_MBUTTONDOWN:  #  Middle click to draw the outline 
        mask = np.zeros(img.shape, np.uint8)
        points = np.array(pts, np.int32)
        points = points.reshape((-1, 1, 2))
        #  Draw a polygon 
        mask = cv2.polylines(mask, [points], True, (255, 255, 255), 2)
        mask2 = cv2.fillPoly(mask.copy(), [points], (255, 255, 255))  #  Used to find  ROI
        mask3 = cv2.fillPoly(mask.copy(), [points], (0, 255, 0))  #  be used for   The image displayed on the desktop 
 
        show_image = cv2.addWeighted(src1=img, alpha=0.8, src2=mask3, beta=0.2, gamma=0)
 
        cv2.imshow("mask", mask2)
        cv2.imshow("show_img", show_image)
 
        ROI = cv2.bitwise_and(mask2, img)
        cv2.imshow("ROI", ROI)
        cv2.waitKey(0)
 
    if len(pts) > 0:
        #  take pts Draw the last point in 
        cv2.circle(img2, pts[-1], 3, (0, 0, 255), -1)
 
    if len(pts) > 1:
        #  Draw line 
        for i in range(len(pts) - 1):
            cv2.circle(img2, pts[i], 5, (0, 0, 255), -1)  # x ,y  For the coordinates of the place where the mouse clicks 
            cv2.line(img=img2, pt1=pts[i], pt2=pts[i + 1], color=(255, 0, 0), thickness=2)
 
    cv2.imshow('image', img2)
 
 
#  Create images and windows and bind them to callback functions 
img = cv2.imread("./test_image.jpg")
img = imutils.resize(img, width=500)
cv2.namedWindow('image')
cv2.setMouseCallback('image', draw_roi)
print("[INFO]  Left click ： Select point , Right click ： Delete the last selected point , Middle click ： determine ROI Area ")
print("[INFO]  Press ‘S’ Confirm the selection area and save ")
print("[INFO]  Press  ESC  sign out ")
 
while True:
    key = cv2.waitKey(1) & 0xFF
    if key == 27:
        break
    if key == ord("s"):
        saved_data = {
    
            "ROI": pts
        }
        joblib.dump(value=saved_data, filename="config.pkl")
        print("[INFO] ROI Coordinates have been saved to local .")
        break
cv2.destroyAllWindows()

Reference resources ：
1. Use the mouse to draw a rectangular or polygonal box on the image
2.OpenCV-Python choice ROI（ Rectangles and polygons ）