python opencv鼠标画点之cv2.drawMarker()函数

时间:2022-04-10 16:06:22

前言

这里所谓画点的意思是指在单一像素点上画一个标记符,而不是画小圆点。使用的函数是cv2.drawMarker(img, position, color, ...)

关于鼠标回调函数的说明可以参考:opencv-python的鼠标交互操作

cv2.drawMarker()函数说明

参数说明

导入cv2后,通过help(cv2.drawMarker)可以看到函数的帮助文档如下:

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drawMarker(...)
    drawMarker(img, position, color[, markerType[, markerSize[, thickness[, line_type]]]]) -> img
    .   @brief Draws a marker on a predefined position in an image.
    .  
    .   The function cv::drawMarker draws a marker on a given position in the image. For the moment several
    .   marker types are supported, see #MarkerTypes for more information.
    .  
    .   @param img Image.
    .   @param position The point where the crosshair is positioned.
    .   @param color Line color.
    .   @param markerType The specific type of marker you want to use, see #MarkerTypes
    .   @param thickness Line thickness.
    .   @param line_type Type of the line, See #LineTypes
    .   @param markerSize The length of the marker axis [default = 20 pixels]

其中三个必选参数:img, position, color,其他参数是可选。三个必选参数说明如下:

  • img:底图,uint8类型的ndarray,
  • position:坐标,是一个包含两个数字的tuple(必需是tuple),表示(x, y)
  • color:颜色,是一个包含三个数字的tuple或list,表示(b, g, r)

其他参数说明如下:

  • markerType:点的类型。取值0-6,有相应的宏定义与之对应,具体的可参考下面的一个表。
  • markerSize:点的大小。大于0的整数,必需是整数。实际输入<=0的数字也可,但是估计程序里有判断,<=0等同于1。默认值是20。
  • thickness:点的线宽。必需是大于0的整数,必需是整数,不能小于0,默认值是1。
  • line_type:线的类型。可以取的值有cv2.LINE_4,cv2.LINE_8,cv2.LINE_AA。其中cv2.LINE_AA的AA表示抗锯齿,线会更平滑。

markerType取值说明

数值 宏定义 说明
0 cv2.MARKER_CROSS 十字线(横竖两根线)
1 cv2.MARKER_TILTED_CROSS 交叉线(斜着两根线)
2 cv2.MARKER_STAR 米字线(横竖加斜着共四根线)
3 cv2.MARKER_DIAMOND 旋转45度的正方形
4 cv2.MARKER_SQUARE 正方形
5 cv2.MARKER_TRIANGLE_UP 尖角向上的三角形
6 cv2.MARKER_TRIANGLE_DOWN 尖角向下的三角形

markerType示例

下面是一个简单的画点程序

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# -*- coding: utf-8 -*-
 
import cv2
import numpy as np
 
if __name__ == '__main__':
    image = np.zeros((256, 256, 3), np.uint8)
    color = (0, 255, 0)
    cv2.drawMarker(image, (50, 50), color, markerType=0)
    cv2.drawMarker(image, (100, 50), color, markerType=1)
    cv2.drawMarker(image, (150, 50), color, markerType=2)
    cv2.drawMarker(image, (200, 50), color, markerType=3)
    cv2.drawMarker(image, (50, 100), color, markerType=4)
    cv2.drawMarker(image, (100, 100), color, markerType=5)
    cv2.drawMarker(image, (150, 100), color, markerType=6)
    cv2.namedWindow('marker_type', 1)
    cv2.imshow('marker_type', image)
    cv2.waitKey(0)
    cv2.destroyAllWindows()

请特别注意,opencv在调用这些画图函数后,image的内容会被这些画图函数改变,也就是说,函数调用之后,我们就拿不回原始的image了,除非另外保存一份原始image的副本。在写一些交互画图函数时,这个特性需要格外注意。

程序执行结果如下。

python opencv鼠标画点之cv2.drawMarker()函数

利用鼠标回调函数交互式画点

例1,简单的例子

该例子与 中的例子相同

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# -*- coding: utf-8 -*-
 
import cv2
import numpy as np
 
WIN_NAME = 'pick_points'
 
 
def onmouse_pick_points(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDOWN:
        print('x = %d, y = %d' % (x, y))
        cv2.drawMarker(param, (x, y), (0, 255, 0))
 
 
if __name__ == '__main__':
    image = np.zeros((256, 256, 3), np.uint8)
    cv2.namedWindow(WIN_NAME, 0)
    cv2.setMouseCallback(WIN_NAME, onmouse_pick_points, image)
    while True:
        cv2.imshow(WIN_NAME, image)
        key = cv2.waitKey(30)
        if key == 27# ESC
            break
    cv2.destroyAllWindows()

上面程序中有几个注意点:

  • setMouseCallback()中的param参数我们传递了image进去,也就是说鼠标回调函数onmouse_pick_points()中的param就是image,画点的操作在鼠标回调函数中,该参数在onmouse_pick_points中的变化可以保留到函数外,可以理解为C++的引用传递,或C语言的指针传递。
  • 需要一个无限循环来刷新图像。
  • 无限循环的退出条件由键盘获取,cv2.waitKey()用来获取键盘的按键,当我们点ESC后就可以退出。

这里点了三次左键,终端输出以下内容:

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x = 60, y = 55
x = 206, y = 113
x = 114, y = 192

并得到这样一张图像:

python opencv鼠标画点之cv2.drawMarker()函数

例2,删除功能

如果需要删除已经画了的点的功能,那么问题就变得略有些复杂了。

我们之前讲过,opencv在画了这些点之后,图像的像素已经事实上被改变了,想要紧紧通过当前图像将其恢复原状是不行的。所以为了实现删除功能,我们需要备份一张原始图像,一张用来对外显示的图像,以及一个由点坐标组成的list。

每次做删除点的操作后,我们都使用原始图像重置对外显示的图像,然后再把list中所有的点都重新画在对外显示的图像上,就可以实现删除点的效果。如果是增加点的操作,则不用重置图像。

实现代码如下:

下面代码中,左键实现增加一个点的操作,右键依次删除后面画上的点。

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# -*- coding: utf-8 -*-
 
import cv2
import numpy as np
 
WIN_NAME = 'pick_points'
 
 
class DrawPoints(object):
    def __init__(self, image, color,
                 marker_type=cv2.MARKER_CROSS,
                 marker_size=20,
                 thickness=1):
        """
        Initialization of class DrawPoints
 
        Parameters
        ----------
        image: ndarray
            source image. shape is [height, width, channels]
        color: tuple
            a tuple containing uint8 integers, designating B, G, R values,
            separately
        marker_type: int
            marker type, between [0, 6]
        marker_size: int
            marker size, >=1
        thickness: int
            line thickness, >=1
        """
        self.original_image = image
        self.image_for_show = image.copy()
        self.color = color
        self.marker_type = marker_type
        self.marker_size = marker_size
        self.thickness = thickness
        self.pts = []
 
    def append(self, x, y):
        """
        add a point to points list
 
        Parameters
        ----------
        x, y: int, int
            coordinate of a point
        """
        self.pts.append((x, y))
 
    def pop(self):
        """
        pop a point from points list
        """
        pt = ()
        if self.pts:
            pt = self.pts.pop()
        return pt
 
    def reset_image(self):
        """
        reset image_for_show using original image
        """
        self.image_for_show = self.original_image.copy()
 
    def draw(self):
        """
        draw points on image_for_show
        """
        for pt in self.pts:
            cv2.drawMarker(self.image_for_show, pt, color=self.color,
                           markerType=self.marker_type,
                           markerSize=self.marker_size,
                           thickness=self.thickness)
 
 
def onmouse_pick_points(event, x, y, flags, draw_pts):
    if event == cv2.EVENT_LBUTTONDOWN:
        print('add: x = %d, y = %d' % (x, y))
        draw_pts.append(x, y)
        draw_pts.draw()
    elif event == cv2.EVENT_RBUTTONDOWN:
        pt = draw_pts.pop()
        if pt:
            print('delete: x = %d, y = %d' % (pt[0], pt[1]))
            draw_pts.reset_image()
            draw_pts.draw()
 
 
if __name__ == '__main__':
    image = np.zeros((256, 256, 3), np.uint8)
    draw_pts = DrawPoints(image, (0, 255, 0))
    cv2.namedWindow(WIN_NAME, 0)
    cv2.setMouseCallback(WIN_NAME, onmouse_pick_points, draw_pts)
    while True:
        cv2.imshow(WIN_NAME, draw_pts.image_for_show)
        key = cv2.waitKey(30)
        if key == 27# ESC
            break
    cv2.destroyAllWindows()

终端输出如下:

add: x = 54, y = 51
add: x = 215, y = 81
add: x = 123, y = 121
add: x = 57, y = 197
add: x = 168, y = 210
delete: x = 168, y = 210
delete: x = 57, y = 197

得到的结果如下:

python opencv鼠标画点之cv2.drawMarker()函数

总结

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原文链接:https://blog.csdn.net/bby1987/article/details/107302373