opencv-python鼠标画瞄准星：cv2.circle()和cv2.line()

一时失言乱红尘 2023-02-25 10:26 138阅读 0赞

### 文章目录 ###

*  函数说明
 *   *  cv2.circle()
     *  cv2.line()
 *  简单的例子
 *  利用鼠标回调函数画瞄准星

所谓`瞄准星`指的是一个圆圈加一个圆圈内的十字线，就像玩射击游戏狙击枪开镜的样子一样。这里并不是直接在图上画一个瞄准星，而是让这个瞄准星跟着鼠标走。在图像标注任务中，可以利用瞄准星进行一些辅助，特别是回归类的任务，使用该功能可以使得关键点的标注更加精准。

关于鼠标回调函数的说明可以参考：[opencv-python的鼠标交互操作][opencv-python]

# 函数说明 #

`import cv2`后，可以分别help(cv2.circle)和help(cv2.line)查看两个函数的帮助信息：

## cv2.circle() ##

circle(...)
        circle(img, center, radius, color[, thickness[, lineType[, shift]]]) -> img
        .   @brief Draws a circle.
        .   
        .   The function cv::circle draws a simple or filled circle with a given center and radius.
        .   @param img Image where the circle is drawn.
        .   @param center Center of the circle.
        .   @param radius Radius of the circle.
        .   @param color Circle color.
        .   @param thickness Thickness of the circle outline, if positive. Negative values, like #FILLED,
        .   mean that a filled circle is to be drawn.
        .   @param lineType Type of the circle boundary. See #LineTypes
        .   @param shift Number of fractional bits in the coordinates of the center and in the radius value.

其中四个必选参数：

*  img：底图，uint8类型的ndarray
 *  center：圆心坐标，是一个包含两个数字的tuple（必需是tuple），表示(x, y)
 *  radius：圆半径，必需是整数
 *  color：颜色，是一个包含三个数字的tuple或list，表示(b, g, r)

其他是可选参数：

*  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
 *  lineType：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，画圆的时候使用该类型比较好。

## cv2.line() ##

line(img, pt1, pt2, color[, thickness[, lineType[, shift]]]) -> img
        .   @brief Draws a line segment connecting two points.
        .   
        .   The function line draws the line segment between pt1 and pt2 points in the image. The line is
        .   clipped by the image boundaries. For non-antialiased lines with integer coordinates, the 8-connected
        .   or 4-connected Bresenham algorithm is used. Thick lines are drawn with rounding endings. Antialiased
        .   lines are drawn using Gaussian filtering.
        .   
        .   @param img Image.
        .   @param pt1 First point of the line segment.
        .   @param pt2 Second point of the line segment.
        .   @param color Line color.
        .   @param thickness Line thickness.
        .   @param lineType Type of the line. See #LineTypes.
        .   @param shift Number of fractional bits in the point coordinates.

其中四个必选参数：

*  img：底图，uint8类型的ndarray
 *  pt1：起点坐标，是一个包含两个数字的tuple（必需是tuple），表示(x, y)
 *  pt2：终点坐标，类型同上
 *  color：颜色，是一个包含三个数字的tuple或list，表示(b, g, r)

其他是可选参数：

# 简单的例子 #

# -*- coding: utf-8 -*-
    
    import cv2
    import numpy as np
    
    
    def imshow(winname, image):
        cv2.namedWindow(winname, 1)
        cv2.imshow(winname, image)
        cv2.waitKey(0)
        cv2.destroyAllWindows()
    
    
    if __name__ == '__main__':
        image = np.zeros((256, 256, 3), np.uint8)
        center = (128, 128)
        radius = 50
        color = (0, 255, 0)
        thickness = 2
    
        pt_left = (center[0] - radius, center[1])
        pt_right = (center[0] + radius, center[1])
        pt_top = (center[0], center[1] - radius)
        pt_bottom = (center[0], center[1] + radius)
    
        cv2.circle(image, center, radius, color, thickness, lineType=cv2.LINE_AA)
        cv2.line(image, pt_left, pt_right, color, thickness)
        cv2.line(image, pt_top, pt_bottom, color, thickness)
        imshow('draw_crosshair', image)

结果如下：  
![在这里插入图片描述][20200717211518626.png]

# 利用鼠标回调函数画瞄准星 #

操作说明：

*  鼠标移动时以鼠标为圆心跟随一个瞄准星
 *  鼠标滚轮控制瞄准星的大小
 *  `+, -`号控制鼠标滚轮时瞄准星的变化量

代码如下：

# -*- coding: utf-8 -*-
    
    import cv2
    
    WIN_NAME = 'draw_crosshair'
    
    
    class DrawCrosshair(object):
        def __init__(self, image, color, center, radius, thickness=1):
            self.original_image = image
            self.image_for_show = image.copy()
            self.color = color
            self.center = center
            self.radius = radius
            self.thichness = thickness
            self.increment = 5
    
        def increase_radius(self):
            self.radius += self.increment
    
        def decrease_radius(self):
            self.radius -= self.increment
            self.radius = max(self.radius, 0)
    
        def increase_increment(self):
            self.increment += 1
    
        def decrease_increment(self):
            self.increment -= 1
            self.increment = max(self.increment, 1)
    
        def reset_image(self):
            """ reset image_for_show using original image """
            self.image_for_show = self.original_image.copy()
    
        def draw_circle(self):
            cv2.circle(self.image_for_show,
                       center=self.center,
                       radius=self.radius,
                       color=self.color,
                       thickness=self.thichness,
                       lineType=cv2.LINE_AA)
    
        def draw_crossline(self):
            pt_left = (self.center[0] - self.radius, self.center[1])
            pt_right = (self.center[0] + self.radius, self.center[1])
            pt_top = (self.center[0], self.center[1] - self.radius)
            pt_bottom = (self.center[0], self.center[1] + self.radius)
            cv2.line(self.image_for_show, pt_left, pt_right,
                     self.color, self.thichness)
            cv2.line(self.image_for_show, pt_top, pt_bottom,
                     self.color, self.thichness)
    
        def draw(self):
            self.reset_image()
            self.draw_circle()
            self.draw_crossline()
    
    
    def onmouse_draw_rect(event, x, y, flags, draw_crosshair):
        if event == cv2.EVENT_MOUSEWHEEL and flags > 0:
            draw_crosshair.increase_radius()
        if event == cv2.EVENT_MOUSEWHEEL and flags < 0:
            draw_crosshair.decrease_radius()
    
        draw_crosshair.center = (x, y)
        draw_crosshair.draw()
    
    
    if __name__ == '__main__':
        # image = np.zeros((512, 512, 3), np.uint8)
        image = cv2.imread('luka.jpg')
        draw_crosshair = DrawCrosshair(image,
                                       color=(0, 255, 0),
                                       center=(256, 256),
                                       radius=100,
                                       thickness=2)
        cv2.namedWindow(WIN_NAME, 1)
        cv2.setMouseCallback(WIN_NAME, onmouse_draw_rect, draw_crosshair)
        while True:
            cv2.imshow(WIN_NAME, draw_crosshair.image_for_show)
            key = cv2.waitKey(30)
            if key == 27:  # ESC
                break
            elif key == ord('+'):
                draw_crosshair.increase_increment()
            elif key == ord('-'):
                draw_crosshair.decrease_increment()
        cv2.destroyAllWindows()

结果如下，有了瞄准星的辅助，我们可以更加精准地找到Luka的眼睛中心。同理，我们在做人脸关键点标注时，这个功能也可以让我们更加精准地找到人眼睛的中心。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JieTE5ODc_size_16_color_FFFFFF_t_70]

[opencv-python]: https://blog.csdn.net/bby1987/article/details/107304679
[20200717211518626.png]: /images/20230209/77a75e44cc0e4058a985f8eb3c3a2bd2.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JieTE5ODc_size_16_color_FFFFFF_t_70]: /images/20230209/8fbae1ed895842f3a5530ee0f5d50794.png