使用 Python OpenCV 库单击鼠标在图像上绘制线条

Question

我正在尝试使用鼠标操作在图像上画一条线。 我正在使用 OpenCV 库。 我的代码

import matplotlib.pyplot as plt
import cv2

src_window = 'CV2 Window'
SHOW_DEBUG_STEPS = True

drag = 0
select_flag = 0
x1 = 0
x2 = 0
y1 = 0
y2 = 0

point1 = [x1,y1]
point2 = [x2,y2]
SCALAR_YELLOW = (0.0,255.0,255.0)

cap = cv2.VideoCapture('example_01.mp4')

def closeAll():
    cap.release()
    cv2.destroyAllWindows()

def retn(ret):
    if not ret:
        print('Error reading the frame')
        closeAll()
        
def frm(fFrame):
    if fFrame is None:
        print('Error reading the frame')
        closeAll()
        

def drawMyLine(frame):
    global point1
    global point2
    cv2.line(frame,(point1[0],point1[1]),(point2[0],point2[1]),SCALAR_YELLOW,2,8)
        
        
def myMouseHandler(event,x,y,flags,param):
    global point1
    global point2
    global drag
    global select_flag
    global callback
    
    if (event==cv2.EVENT_LBUTTONDOWN and not(drag) and not(select_flag)):
        print('case 1')
        point1=[x,y]
        drag = 1
        
    if (event == cv2.EVENT_MOUSEMOVE and drag and not(select_flag)):
        print('case 2')
        img1 = fFrame.copy()
        point2 = [x,y]
        drawMyLine(img1)
        
    if (event == cv2.EVENT_LBUTTONUP and drag and not(select_flag)):
        print('case 3')
        img2 = fFrame.copy()
        point2 = [x,y]
        drag = 0
        select_flag = 1
        cv2.imshow(src_window,img2) 
        callback = 1
        

if not(cap.isOpened()):
    print('Error reading the video')
    
ret,fFrame = cap.read()
retn(ret)
frm(fFrame)

fGray = cv2.cvtColor(fFrame,cv2.COLOR_BGR2GRAY)

cv2.imshow(src_window,fGray)
cv2.setMouseCallback(src_window,myMouseHandler)
cv2.waitKey(0)

当我运行代码并尝试通过单击鼠标左键来绘制一条线时，将鼠标拖动到第二个点并释放鼠标左键，我看到我的打印语句 case1、case2、case3 正在终端中打印。 但是这条线没有出现。 我不确定我哪里出错了。

Answer 1

要使用鼠标单击在图像上绘制线条，我们必须捕获鼠标单击的事件动作，然后记录开始和结束坐标。 OpenCV 允许我们通过处理鼠标点击事件来做到这一点。 每当触发鼠标单击事件时，OpenCV 都会通过将信息附加到cv2.setMouseCallback处理程序，将信息传递给我们的extract_coordinates回调函数。 为了检测事件，OpenCV 需要各种参数：

• event ：发生的事件（左/右按下或释放鼠标单击）
• x : 事件的 x 坐标
• y : 事件的 y 坐标
• flags : OpenCV 传递的相关标志
• 参数：OpenCV 传递的额外参数

按下左键 ( cv2.EVENT_LBUTTONDOWN ) 记录起始坐标，而松开左键 ( cv2.EVENT_LBUTTONUP ) 记录结束坐标。 然后我们用cv2.line画一条线并将坐标打印到控制台。 右键单击（ cv2.EVENT_RBUTTONDOWN ）将重置图像。 这是一个在图像上绘制线条的简单小部件：

import cv2

class DrawLineWidget(object):
    def __init__(self):
        self.original_image = cv2.imread('1.jpg')
        self.clone = self.original_image.copy()

        cv2.namedWindow('image')
        cv2.setMouseCallback('image', self.extract_coordinates)

        # List to store start/end points
        self.image_coordinates = []

    def extract_coordinates(self, event, x, y, flags, parameters):
        # Record starting (x,y) coordinates on left mouse button click
        if event == cv2.EVENT_LBUTTONDOWN:
            self.image_coordinates = [(x,y)]

        # Record ending (x,y) coordintes on left mouse bottom release
        elif event == cv2.EVENT_LBUTTONUP:
            self.image_coordinates.append((x,y))
            print('Starting: {}, Ending: {}'.format(self.image_coordinates[0], self.image_coordinates[1]))

            # Draw line
            cv2.line(self.clone, self.image_coordinates[0], self.image_coordinates[1], (36,255,12), 2)
            cv2.imshow("image", self.clone) 

        # Clear drawing boxes on right mouse button click
        elif event == cv2.EVENT_RBUTTONDOWN:
            self.clone = self.original_image.copy()

    def show_image(self):
        return self.clone

if __name__ == '__main__':
    draw_line_widget = DrawLineWidget()
    while True:
        cv2.imshow('image', draw_line_widget.show_image())
        key = cv2.waitKey(1)

        # Close program with keyboard 'q'
        if key == ord('q'):
            cv2.destroyAllWindows()
            exit(1)

Answer 2

您的代码有几个问题。

1) img1 = fFrame.copy()实例化img1然后你在它上面画图，作为一个局部变量你再也不会使用它，导致你失去你画的东西。 相反，在实际框架上绘制如下。

if (event == cv2.EVENT_MOUSEMOVE and drag and not(select_flag)):
   print('case 2')
   point2 = [x,y]
   drawMyLine(fFrame)

2) 绘制当前行后，您应该将下一行的开头 (next point1 ) 更新为当前行的结尾 (current point2 )。

if (event == cv2.EVENT_MOUSEMOVE and drag and not(select_flag)):
    print('case 2')
    point2 = [x,y]
    drawMyLine(fFrame)
    point1 = [x,y] # <-- update for next draw

3）这是可选的，你可以直接显示当前帧，而不是img2 。

if (event == cv2.EVENT_LBUTTONUP and drag and not(select_flag)):
    print('case 3')
    point2 = [x,y]
    drag = 0
    select_flag = 1
    cv2.imshow(src_window,fFrame)
    callback = 1

4）这也是可选的，但是为了在点击结束时正确绘制最后一行，你应该在这种情况下最后一次调用draw函数。

if (event == cv2.EVENT_LBUTTONUP and drag and not(select_flag)):
    print('case 3')
    point2 = [x,y]
    drawMyLine(fFrame) # <-- draw the last line
    drag = 0
    select_flag = 1
    cv2.imshow(src_window,fFrame)
    callback = 1

总的来说，其余的代码都是一样的，更新的鼠标处理程序如下。

def myMouseHandler(event,x,y,flags,param):
    global drag
    global select_flag
    global callback
    global point1
    global point2

    if (event==cv2.EVENT_LBUTTONDOWN and not(drag) and not(select_flag)):
        print('case 1')
        point1=[x,y]
        drag = 1

    if (event == cv2.EVENT_MOUSEMOVE and drag and not(select_flag)):
        print('case 2')
        point2 = [x,y]
        drawMyLine(fFrame)
        point1 = [x,y]

    if (event == cv2.EVENT_LBUTTONUP and drag and not(select_flag)):
        print('case 3')
        point2 = [x,y]
        drawMyLine(fFrame)
        drag = 0
        select_flag = 1
        cv2.imshow(src_window,fFrame)
        callback = 1

Answer 3

import cv2
import numpy as np
def click_event(event,x,y,flags,param):
    if event == cv2.EVENT_LBUTTONDOWN:
        cv2.circle(img,(x,y),3,(255,0,0),-1)
        points.append((x,y))
        if len(points) >= 2:
            cv2.line(img,points[-1],points[-2],(0,255,0),1)
        cv2.imshow("image", img)
cv2.imshow("image",img)
points = []
cv2.setMouseCallback('image',click_event)
cv2.waitKey(0)