opencv-python鼠标画矩形框：cv2.rectangle()

た入场券 2023-02-25 10:26 165阅读 0赞

### 文章目录 ###

*  cv2.rectangle()函数说明
 *   *  参数说明
 *  利用鼠标回调函数交互式画矩形框

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]

# cv2.rectangle()函数说明 #

## 参数说明 ##

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

rectangle(...)
        rectangle(img, pt1, pt2, color[, thickness[, lineType[, shift]]]) -> img
        .   @brief Draws a simple, thick, or filled up-right rectangle.
        .   
        .   The function cv::rectangle draws a rectangle outline or a filled rectangle whose two opposite corners
        .   are pt1 and pt2.
        .   
        .   @param img Image.
        .   @param pt1 Vertex of the rectangle.
        .   @param pt2 Vertex of the rectangle opposite to pt1 .
        .   @param color Rectangle color or brightness (grayscale image).
        .   @param thickness Thickness of lines that make up the rectangle. Negative values, like #FILLED,
        .   mean that the function has to draw a filled rectangle.
        .   @param lineType Type of the line. See #LineTypes
        .   @param shift Number of fractional bits in the point coordinates.
        
        
        
        rectangle(img, rec, color[, thickness[, lineType[, shift]]]) -> img
        .   @overload
        .   
        .   use `rec` parameter as alternative specification of the drawn rectangle: `r.tl() and
        .   r.br()-Point(1,1)` are opposite corners

其中四个参数必选：

*  img：底图，uint8类型的ndarray
 *  pt1：矩形框的一个顶点坐标，是一个包含两个数字的tuple（必需是tuple），表示(x, y)
 *  pt2：pt1的对角线顶点坐标，类型同pt1
 *  color：颜色，是一个包含三个数字的tuple或list，表示(b, g, r)；如果图片是灰度图的话，color也可以是一个数字

其他参数说明如下：

*  thickness：线宽，默认值是1，数值越大表示线宽越宽；如果取值为负数或者cv2.FILLED，那么将画一个填充了的矩形
 *  lineType：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。

注意：pt1和pt2表示任意一对对角线上的点，不一定要求pt1必需左上角，pt2必需右下角。另外pt1和pt2可以互换顺序而不影响结果。

下面是一个非交互式的程序示例

# -*- 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.rectangle(image, (20, 20), (60, 60), (0, 255, 0))
        cv2.rectangle(image, (120, 120), (80, 80), (255, 0, 0), thickness=-1)
        cv2.rectangle(image, (140, 200), (200, 140), (0, 0, 255), thickness=5)
        cv2.namedWindow('rect', 1)
        cv2.imshow('rect', image)
        cv2.waitKey(0)
        cv2.destroyAllWindows()

第一个矩形框`pt1 = 左上角，pt2 = 右下角`  
第二个矩形框`pt1 = 右下角，pt2 = 左上角`  
第三个矩形框`pt1 = 右上角，pt2 = 左下角`

得到的结果如下：  
![在这里插入图片描述][20200715213510577.png]

# 利用鼠标回调函数交互式画矩形框 #

为了容易理解下面程序，建议先参考下面文章的`例2`  
[opencv-python鼠标画点：cv2.drawMarker()][opencv-python_cv2.drawMarker]

下面程序的操作方法是：

*  鼠标左键按下开始画当前矩形框
 *  移动鼠标进行绘画
 *  弹起左键当前矩形框绘画结束，并把当前矩形框加入列表
 *  鼠标右键按下是删除矩形框列表中的最后一个对象

编程注意事项：

*  矩形框绘画过程中需要记录一个鼠标左键按下的状态标志。常规状态下该标志设为False，鼠标移动不进行绘画；当鼠标左键按下后，标志设为True，此时移动鼠标将进入绘画状态；左键弹起后，标志恢复False。
 *  为了在鼠标移动过程中实时显示绘画状态，需要不停地重置用来显示的图像，并不停地重画所有已保存的矩形框
 *  矩形框的第二个点使用shrink\_point获取，确保不超出图像边界

# -*- coding: utf-8 -*-
    
    import copy
    import cv2
    import numpy as np
    
    WIN_NAME = 'draw_rect'
    
    
    class Rect(object):
        def __init__(self):
            self.tl = (0, 0)
            self.br = (0, 0)
    
        def regularize(self):
            """ make sure tl = TopLeft point, br = BottomRight point """
            pt1 = (min(self.tl[0], self.br[0]), min(self.tl[1], self.br[1]))
            pt2 = (max(self.tl[0], self.br[0]), max(self.tl[1], self.br[1]))
            self.tl = pt1
            self.br = pt2
    
    
    class DrawRects(object):
        def __init__(self, image, color, thickness=1):
            self.original_image = image
            self.image_for_show = image.copy()
            self.color = color
            self.thickness = thickness
            self.rects = []
            self.current_rect = Rect()
            self.left_button_down = False
    
        @staticmethod
        def __clip(value, low, high):
            """ clip value between low and high Parameters ---------- value: a number value to be clipped low: a number low limit high: a number high limit Returns ------- output: a number clipped value """
            output = max(value, low)
            output = min(output, high)
            return output
    
        def shrink_point(self, x, y):
            """ shrink point (x, y) to inside image_for_show Parameters ---------- x, y: int, int coordinate of a point Returns ------- x_shrink, y_shrink: int, int shrinked coordinate """
            height, width = self.image_for_show.shape[0:2]
            x_shrink = self.__clip(x, 0, width)
            y_shrink = self.__clip(y, 0, height)
            return (x_shrink, y_shrink)
    
        def append(self):
            """ add a rect to rects list """
            self.rects.append(copy.deepcopy(self.current_rect))
    
        def pop(self):
            """ pop a rect from rects list """
            rect = Rect()
            if self.rects:
                rect = self.rects.pop()
            return rect
    
        def reset_image(self):
            """ reset image_for_show using original image """
            self.image_for_show = self.original_image.copy()
    
        def draw(self):
            """ draw rects on image_for_show """
            for rect in self.rects:
                cv2.rectangle(self.image_for_show, rect.tl, rect.br,
                              color=self.color, thickness=self.thickness)
    
        def draw_current_rect(self):
            """ draw current rect on image_for_show """
            cv2.rectangle(self.image_for_show,
                          self.current_rect.tl, self.current_rect.br,
                          color=self.color, thickness=self.thickness)
    
    
    def onmouse_draw_rect(event, x, y, flags, draw_rects):
        if event == cv2.EVENT_LBUTTONDOWN:
            # pick first point of rect
            print('pt1: x = %d, y = %d' % (x, y))
            draw_rects.left_button_down = True
            draw_rects.current_rect.tl = (x, y)
        if draw_rects.left_button_down and event == cv2.EVENT_MOUSEMOVE:
            # pick second point of rect and draw current rect
            draw_rects.current_rect.br = draw_rects.shrink_point(x, y)
            draw_rects.reset_image()
            draw_rects.draw()
            draw_rects.draw_current_rect()
        if event == cv2.EVENT_LBUTTONUP:
            # finish drawing current rect and append it to rects list
            draw_rects.left_button_down = False
            draw_rects.current_rect.br = draw_rects.shrink_point(x, y)
            print('pt2: x = %d, y = %d' % (draw_rects.current_rect.br[0],
                                           draw_rects.current_rect.br[1]))
            draw_rects.current_rect.regularize()
            draw_rects.append()
        if (not draw_rects.left_button_down) and event == cv2.EVENT_RBUTTONDOWN:
            # pop the last rect in rects list
            draw_rects.pop()
            draw_rects.reset_image()
            draw_rects.draw()
    
    
    if __name__ == '__main__':
        image = np.zeros((256, 256, 3), np.uint8)
        draw_rects = DrawRects(image, (0, 255, 0), 2)
        cv2.namedWindow(WIN_NAME, 0)
        cv2.setMouseCallback(WIN_NAME, onmouse_draw_rect, draw_rects)
        while True:
            cv2.imshow(WIN_NAME, draw_rects.image_for_show)
            key = cv2.waitKey(30)
            if key == 27:  # ESC
                break
        cv2.destroyAllWindows()

终端输出：

pt1: x = 55, y = 68
    pt2: x = 0, y = 0
    pt1: x = 195, y = 60
    pt2: x = 256, y = 0
    pt1: x = 59, y = 192
    pt2: x = 0, y = 256
    pt1: x = 194, y = 190
    pt2: x = 256, y = 256
    pt1: x = 94, y = 111
    pt2: x = 170, y = 168

结果如下：  
![在这里插入图片描述][202007152321328.png]

[opencv-python]: https://blog.csdn.net/bby1987/article/details/107304679
[20200715213510577.png]: /images/20230209/87cc7e30ba5f408c92a00c585d0f38b9.png
[opencv-python_cv2.drawMarker]: https://blog.csdn.net/bby1987/article/details/107302373
[202007152321328.png]: /images/20230209/03ae746a30614f78a03fd0db671c50d3.png