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
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:
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。
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:
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。
# -*- 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:
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。