cv2在图像上画不同比例的锚框

'''
        cv2在图像上画不同比例的锚框
'''
import cv2
import math

# 画宽高比1:1的锚框
def display_11_anchor(img,anchor_11_left_top,anchor_11_right_bottom):
    cv2.rectangle(img,
              anchor_11_left_top,
              anchor_11_right_bottom,
              (0, 255, 0),      # 颜色：G
              2)

# 画宽高比1:2的锚框
def display_12_anchor(img,anchor_12_left_top,anchor_12_right_bottom):
    cv2.rectangle(img,
              anchor_12_left_top,
              anchor_12_right_bottom,
              (255, 0, 0),      # 颜色：B
              2)

# 画宽高比2:1的锚框
def display_21_anchor(img,anchor_21_left_top,anchor_21_right_bottom):
    cv2.rectangle(img,
              anchor_21_left_top,
              anchor_21_right_bottom,
              (0, 0, 255),      # 颜色：R
              2)

# 画出所有锚框，size代表锚框面积占一个网格面积的百分比
def display_anchor(img,anchor_rows,anchor_columns,size):
    heigh,width,channel = img.shape
    area=heigh*width    # 图片面积
    grid_area=int(area//(anchor_rows*anchor_columns)*size)  # 网格面积
    anchor_11_width=math.sqrt(grid_area)    # 宽高比1:1的锚框宽度
    anchor_11_heigh=anchor_11_width         # 宽高比1:1的锚框高度
    anchor_12_width=math.sqrt(grid_area/2)  # 宽高比1:2的锚框宽度
    anchor_12_heigh=2*anchor_12_width       # 宽高比1:2的锚框高度
    anchor_21_width=anchor_12_heigh         # 宽高比2:1的锚框宽度
    anchor_21_heigh=anchor_12_width         # 宽高比2:1的锚框高度

    grid_edge_width=width//anchor_columns   # 一个网格的宽度
    grid_edge_heigh=heigh//anchor_rows      # 一个网格的高度

    for i in range(anchor_rows):    # 遍历所有的网格
        for j in range(anchor_columns):
            grid_left_top=[grid_edge_width*j,grid_edge_heigh*i]     # 网格的左上顶点
            grid_right_bottom=[grid_edge_width*(j+1),grid_edge_heigh*(i+1)]     # 网格的右下顶点

            grid_centre=[(grid_right_bottom[0]-grid_left_top[0])//2+grid_left_top[0],   # 找到网格的中心
                         (grid_right_bottom[1]-grid_left_top[1])//2+grid_left_top[1]]

            # 分别计算三种宽高比的锚框的左上和右下顶点
            anchor_11_left_top=(int(grid_centre[0]-anchor_11_width//2),int(grid_centre[1]-anchor_11_heigh//2))
            anchor_11_right_bottom=(int(grid_centre[0]+anchor_11_width//2),int(grid_centre[1]+anchor_11_heigh//2))
            anchor_12_left_top=(int(grid_centre[0]-anchor_12_width//2),int(grid_centre[1]-anchor_12_heigh//2))
            anchor_12_right_bottom=(int(grid_centre[0]+anchor_12_width//2),int(grid_centre[1]+anchor_12_heigh//2))
            anchor_21_left_top=(int(grid_centre[0]-anchor_21_width//2),int(grid_centre[1]-anchor_21_heigh//2))
            anchor_21_right_bottom=(int(grid_centre[0]+anchor_21_width//2),int(grid_centre[1]+anchor_21_heigh//2))

            # 根据顶点画出矩形
            display_11_anchor(img,anchor_11_left_top,anchor_11_right_bottom)
            display_12_anchor(img,anchor_12_left_top,anchor_12_right_bottom)
            display_21_anchor(img,anchor_21_left_top,anchor_21_right_bottom)

    cv2.imshow('image', img)
    cv2.waitKey(0)
    cv2.destroyAllWindows()

if __name__ == '__main__':

    img_path = 'catdog.jpg'
    img = cv2.imread(img_path)
    display_anchor(img,anchor_rows=6,anchor_columns=6,size=0.4)

最终的显示效果如图：

图1 宽高比：6:6

图2 宽高比：3:6

图3 宽高比：6:3