如何让 matplotlib 的 imshow 生成图像而不被绘制

问题描述

Matplotlib 的 imshow 在绘制 numpy 数组方面做得很好.这段代码最好地说明了这一点:

Matplotlib's imshow does a nice job of plotting a numpy array. This is best illustrated by this code:

from PIL import Image
import matplotlib.pyplot as plt
import numpy as np
rows, cols = 200, 200
mat = np.zeros ((rows, cols))
for r in range(rows):
    for c in range(cols):
        mat[r, c] = r * c
# Handle with matplotlib
plt.imshow(mat)

及其创建的图形:，这就是我想要的.我想要的是没有轴的图像，所以通过谷歌搜索我能够组装这个功能:

and the figure it creates: , which is about what I want. What I want is the image without axes, so by googling around I was able to assemble this function:

def create_img (image, w, h):
    fig = plt.figure(figsize=(w, h), frameon=False)
    canvas = FigureCanvas(fig)
    #To make the content fill the whole figure
    ax = plt.Axes(fig, [0., 0., 1., 1.])
    ax.set_axis_off()
    fig.add_axes(ax)
    plt.grid(False)
    ax.imshow(image, aspect='auto', cmap='viridis')
    canvas.draw()
    buf = fig.canvas.tostring_rgb()
    ncols, nrows = fig.canvas.get_width_height()
    a = np.fromstring(buf, dtype=np.uint8).reshape(nrows, ncols, 3)
    plt.close()
    plt.pause(0.01)
    return Image.fromarray(a)

它从一个 numpy 矩阵生成一个图像.它没有情节，几乎.绘图一会儿，然后图像关闭.我接下来可以保存图像，这一切麻烦的原因是什么.

It generates an image from a numpy matrix. And it does not plot, well almost. It plots for a brief moment but then the image closes. I next can save the image what was the reason for all this hassle.

我想知道是否有更简单的方法可以达到相同的目标.我尝试使用枕头，通过在第一个示例的代码后面添加一些语句:

I wondered whether there was a simpler method to reach the same goal. I tried to use pillow, by adding some statements behind the code of the first example:

# Handle with pillow.Image
img = Image.fromarray(mat, 'RGB')
img.show()
img.save('/home/user/tmp/figure.png')

但这会产生一个不全面的图像.可能是由于我的一些错误，但我不知道是哪个.

But that generates an incomprehensive image. Probably due to some mistake of mine but I do not know which.

我不知道如何通过其他方式(例如通过枕头)获取具有类似 imshow 之类输出的numpy数组的图像.有人知道我如何以与 matplotlibs imshow() 相同的方式从 numpy 矩阵生成图像而没有闪烁的图?并且以一种比我使用 create_img 函数构想的方式更简单的方式?

I do not know how to get an image of a numpy array with similar output like imshow by other means, for example by pillow. Does someone know how I can generate an image from a numpy matrix in the same way as matplotlibs imshow() without the flashing plots? And in a simpler way than I have concocted with the create_img function?

推荐答案

这个简单的案例可能最好由 plt.imsave.

This simple case can probably best be handled by plt.imsave.

import matplotlib.pyplot as plt
import numpy as np

rows, cols = 200, 200
r,c = np.meshgrid(np.arange(rows), np.arange(cols))
mat = r*c

# saving as image
plt.imsave("output.png", mat)
# or in some other format
# plt.imsave("output.jpg", mat, format="jpg")

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