在python中绘制图像背景

问题描述

我想使用matplotlib在图像背景上绘制图形。我发现如何在matlab中进行操作

你可以看到我们有一架1600 x 1200的塞缪尔·杰克逊坦率地说，他乘坐的航空公司的航班对这条蛇非常恼火。

但是如果我们想在两个维度上绘制一条范围从0到300的线，我们可以这样做：

  fig，ax = plt.subplots（）
x = range（300）
 ax.imshow（img，extent = [0,400,0,300]）
 ax.plot（x，x，' - '，linewidth = 5，color ='firebrick'）
  

我不知道这条线是否会帮助杰克逊先生解决他的蛇问题。至少，它不会让事情变得更难。

I would like to plot a graph over an image background using matplotlib. I found how to do it in matlab http://www.peteryu.ca/tutorials/matlab/plot_over_image_background

I've tried something basic like this:

im = plt.imread("dd.png")
implot = plt.imshow(im)
theta=np.linspace(0,2*np.pi,50)
z=np.cos(theta)*39+145
t=np.sin(theta)*39+535-78+39
plt.plot(z,t)
plt.show()

but it gave me something really ugly:

解决方案

Just like in the MATLAB example that you linked to, you have to specify the desired extent of the image when you call in imshow.

By default, matplotlib and MATLAB both place the upper left corner of the image the origin, go down and to the right from there, and set each pixel as a 1x1 square in coordinate space. This is what your image is doing.

You can control this with the extent parameter which takes the form of a list [left, right, bottom, top].

Not using extent looks like this:

import matplotlib.pyplot as plt
img = plt.imread("airlines.jpg")
fig, ax = plt.subplots()
ax.imshow(img)

You can see that we have a 1600 x 1200 of Samuel L. Jackson getting, quite frankly, rather annoyed with the snake aboard his airline flight.

But if we want to plot a line ranging from 0 to 300 in both dimension over this, we can do just that:

fig, ax = plt.subplots()
x = range(300)
ax.imshow(img, extent=[0, 400, 0, 300])
ax.plot(x, x, '--', linewidth=5, color='firebrick')

I don't know if the line will help Mr. Jackson with his snake problem. At the very least, it won't make things any harder.

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