OpenCV在一个圆圈上获取像素 [英] OpenCV get pixels on an circle

问题描述

我是OpenCV的新手，我正在尝试从图像中获取圆的像素.

I'm new to OpenCV and I'm trying to get the pixels of a circle from an image.

例如，我在随机图像上画一个圆:

For example, I draw a circle on a random image:

import cv2

raw_img = cv2.imread('sample_picture.png')
x = 50
y = 50
rad = 20
cv2.circle(raw_img,(x,y),rad,(0,255,0),-1)
cv2.imshow('output', raw_img)
cv2.waitKey(0)
cv2.destroyAllWindows()

输出显示带圆圈的图像. 但是，我希望能够以数组的形式返回圆上的所有像素.有什么办法吗?我知道我可以从圆公式中获得近似坐标，但是它将涉及很多十进制计算，而且我很确定函数 cv2.circle() >已经计算了像素，是否有办法从函数本身中获取像素，而不是计算自己的像素?

The output shows an image with a circle. However, I want to be able to get all the pixel on the circle back in the form of an array. Is there any way to do this? I know I can get the approximate coordinates from the circle formula, but it will involve a lot of decimal calculations, and I'm pretty sure that the function cv2.circle() has already calculated the pixel, so is there a way to get it out from the function itself instead of calculating my self?

此外，如果可能的话，我想使用 cv2.ellipse() 作为坐标数组来获取椭圆的像素.但是这一次，我只想从椭圆的一部分(从某个角度到另一个角度，可以在cv2.ellipse()的参数中指定)获取像素.

Also, if it is possible I would like to get the pixel of an ellipse using cv2.ellipse() back as an array of coordinates. But this time, I want to get the pixel only from a part of an ellipse (from a certain angle to another angle, which I can specify in the parameter of cv2.ellipse()).

谢谢.

推荐答案

您可以使用numpy函数实现所需的功能:

You can achieve what you are looking for by using the numpy function:

numpy.where(condition[, x, y])

链接中功能的详细说明: https://docs.scipy.org/doc/numpy-1.15.1/reference/generated/numpy.where.html

Detailed explanation of function in link :https://docs.scipy.org/doc/numpy-1.15.1/reference/generated/numpy.where.html

在您的情况下，您希望它返回具有非零值的坐标.使用此方法，您可以在空数组上绘制任何内容，它将返回与非零相对应的所有行和列.

In your case, you would want to it to return the coordinates that has non-zero values. Using this method, you can draw anything on an empty array and it will return all rows and columns corresponding to non-zeros.

它将返回满足您设置的条件的数组的索引.下面的代码显示了用法示例.

It will return the index of the array that satisfies the condition you set. Below is a code showing an example of the usage.

import cv2
import numpy as np

raw_img = cv2.imread('sample_picture.png')
x = 50
y = 50
rad = 20
cv2.circle(raw_img,(x,y),rad,(0,255,0),-1)

# Here is where you can obtain the coordinate you are looking for
combined = raw_img[:,:,0] + raw_img[:,:,1] + raw_img[:,:,2]
rows, cols, channel = np.where(combined > 0)    

cv2.imshow('output', raw_img)
cv2.waitKey(0)
cv2.destroyAllWindows()

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