imshow(img，cmap = cm.gray)为128值显示白色 [英] imshow(img, cmap=cm.gray) shows a white for 128 value

问题描述

我正从MatLab转到python，并正在使用imshow函数.

I'm moving from MatLab to python and playing around with the imshow function.

我似乎无法理解为什么它没有将128值显示为灰色，而我已将cmap选择为灰度.

I can't seem to get my head around why it doesn't show the value 128 as grey with I have chosen the cmap to be gray-scale.

似乎它对最高(128)和最低值使用灰度..我希望它对[0:255]使用灰度.我该怎么办?

It seems as it uses the grayscale for highest (128) and lowest values.. I want it to use the grayscale for [0:255]. How do I do that?

推荐答案

使用vmin和vmax参数:

plt.imshow(bg, cmap=plt.get_cmap('gray'), vmin=0, vmax=255)

plt.imshow在未指定vmin和vmax的情况下，将其范围自动调整为数据的最小值和最大值.

Without specifying vmin and vmax, plt.imshow auto-adjusts its range to the min and max of the data.

我不知道为所有imshow图设置默认的vmin和vmax参数的方法，但是您可以使用functools.partial来准备一个自定义的类似imshow的命令，并设置默认参数:

I do not know of a way to set default vmin and vmax parameters for all imshow plots, but you could use functools.partial to prepare a custom imshow-like command with default parameters set:

import matplotlib.pyplot as plt
import numpy as np
import functools

bwimshow = functools.partial(plt.imshow, vmin=0, vmax=255,
                             cmap=plt.get_cmap('gray'))

dots = np.random.randn(10, 10)*255
bwimshow(dots)
cbar = plt.colorbar()

plt.show()

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