Matplotlib-无法以与原始图像相同的分辨率保存图像 [英] Matplotlib - unable to save image in same resolution as original image

问题描述

我无法保存没有白色边框和初始分辨率(1037x627)的图像

I am unable to save the image without the white borders and at the initial resolution (1037x627)

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import pyplot, lines
import matplotlib.image as mpimg
from matplotlib.patches import Ellipse
x=[0,0,0,0,0]
y=[0,0,0,0,0]
a=10**1.3*15
inc=25
b=np.cos(np.radians(inc))*a
x[0],y[0]=516.667,313.021
x[1],y[1]=x[0]-a,y[0]
x[2],y[2]=x[0]+a,y[0]
x[3],y[3]=x[0],y[0]+b
x[4],y[4]=x[0],y[0]-b
for pa in range(0,10,5):
    fig, ax = plt.subplots()
    img=mpimg.imread('IC342.png')
    imgplot = plt.imshow(img)
    x[1],y[1]=x[0]-a/2*np.cos(np.radians(pa)),y[0]-a/2*np.sin(np.radians(pa))
    x[2],y[2]=x[0]+a/2*np.cos(np.radians(pa)),y[0]+a/2*np.sin(np.radians(pa))
    x[3],y[3]=x[0]+b/2*np.cos(np.radians(pa+90)),y[0]+b/2*np.sin(np.radians(pa+90))
    x[4],y[4]=x[0]-b/2*np.cos(np.radians(pa+90)),y[0]-b/2*np.sin(np.radians(pa+90))
    ell = Ellipse(xy=[516.667,313.021], width=a, height=b, angle=pa, edgecolor='b',lw=4, alpha=0.5, facecolor='none')
    name='plt'+str(pa)+'.png'
    leg='PA='+str(pa)
    #ax.text(10, 10, leg, fontsize=15,color='white')
    ax.add_artist(ell)
    xn=[x[1],x[2],x[0]]
    yn=[y[1],y[2],y[0]]
    xnw=[x[3],x[4],x[0]]
    ynw=[y[3],y[4],y[0]]
    line = lines.Line2D(xn, yn, linestyle='-.',lw=5., color='r', alpha=0.4)
    line1 = lines.Line2D(xnw, ynw, linestyle='-.',lw=5., color='g', alpha=0.4)
    ax.add_line(line)
    ax.add_line(line1)
    plt.axis('off')
    fig.savefig(name, transparent=True, bbox_inches='tight', pad_inches=0,dpi=150 )

初始图像

结果

我还需要白色文本PA=something出现在图像上，而无需更改分辨率.据我了解，添加其他图形(例如文本)可能会自动更改分辨率.

Also I need the white text PA=something to be on the image without changing the resolution. From what I understand adding another figure like text might automatically change the resolution.

谢谢您的时间！

推荐答案

这里有两个因素在起作用:

There are two factors at play here:

1. 默认情况下，Axes不会占用整个Figure
2. 在matplotlib中，Figure的大小是固定的，并且内容被拉伸/压缩/内插以适合图形.您希望Figure的大小由其内容来定义.

1. An Axes doesn't take up the entire Figure by default
2. In matplotlib, the Figure's size is fixed, and the contents are stretched/squeezed/interpolated to fit the figure. You want the Figure's size to be defined by its contents.

要做您想做的事，分三个步骤:

To do what you want to do, there are three steps:

1. 根据图像的大小和设置的DPI创建图形
2. 添加占用整个图形的子图/轴
3. 使用用于计算图形尺寸的DPI保存图形

我们使用来自美国国家航空航天局(Nasa)的随机哈勃图像 http://www.nasa.gov/sites/default/files/thumbnails/image/hubble_friday_12102015.jpg .这是1280x1216像素的图像.

Let's use a random Hubble image from Nasa http://www.nasa.gov/sites/default/files/thumbnails/image/hubble_friday_12102015.jpg. It's a 1280x1216 pixel image.

以下是一个受到严重评论的示例，可以指导您完成操作:

Here's a heavily commented example to walk you through it:

import matplotlib.pyplot as plt

# On-screen, things will be displayed at 80dpi regardless of what we set here
# This is effectively the dpi for the saved figure. We need to specify it,
# otherwise `savefig` will pick a default dpi based on your local configuration
dpi = 80

im_data = plt.imread('hubble_friday_12102015.jpg')
height, width, nbands = im_data.shape

# What size does the figure need to be in inches to fit the image?
figsize = width / float(dpi), height / float(dpi)

# Create a figure of the right size with one axes that takes up the full figure
fig = plt.figure(figsize=figsize)
ax = fig.add_axes([0, 0, 1, 1])

# Hide spines, ticks, etc.
ax.axis('off')

# Display the image.
ax.imshow(im_data, interpolation='nearest')

# Add something...
ax.annotate('Look at This!', xy=(590, 650), xytext=(500, 500),
            color='cyan', size=24, ha='right',
            arrowprops=dict(arrowstyle='fancy', fc='cyan', ec='none'))

# Ensure we're displaying with square pixels and the right extent.
# This is optional if you haven't called `plot` or anything else that might
# change the limits/aspect.  We don't need this step in this case.
ax.set(xlim=[0, width], ylim=[height, 0], aspect=1)

fig.savefig('test.jpg', dpi=dpi, transparent=True)
plt.show()

保存的test.jpg将恰好是1280x1216像素.当然，由于我们对输入和输出都使用了有损压缩格式，因此由于压缩伪像，您将无法获得完美的像素匹配.但是，如果您使用无损输入和输出格式，则应该这样做.

The saved test.jpg will be exactly 1280x1216 pixels. Of course, because we're using a lossy compressed format for both input and output, you won't get a perfect pixel match due to compression artifacts. If you used lossless input and output formats you should, though.

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