Python 使用 matplotlib 将图像显示为灰度
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Display image as grayscale using matplotlib
提问by Ryan
I'm trying to display a grayscale image using matplotlib.pyplot.imshow(). My problem is that the grayscale image is displayed as a colormap. I need the grayscale because I want to draw on top of the image with color.
我正在尝试使用matplotlib.pyplot.imshow()显示灰度图像。我的问题是灰度图像显示为颜色图。我需要灰度，因为我想用颜色在图像上绘制。
I read in the image and convert to grayscale using PIL's Image.open().convert("L")
我读入图像并使用PIL 的 Image.open().convert("L")转换为灰度
image = Image.open(file).convert("L")Then I convert the image to a matrix so that I can easily do some image processing using
然后我将图像转换为矩阵，以便我可以轻松地使用
matrix = scipy.misc.fromimage(image, 0)However, when I do
但是，当我这样做时
figure()
matplotlib.pyplot.imshow(matrix)
show()it displays the image using a colormap (i.e. it's not grayscale).
它使用颜色图显示图像（即它不是灰度）。
What am I doing wrong here?
我在这里做错了什么？
采纳答案by unutbu
The following code will load an image from a file image.pngand will display it as grayscale.
以下代码将从文件加载图像image.png并将其显示为灰度。
import numpy as np
import matplotlib.pyplot as plt
from PIL import Image
fname = 'image.png'
image = Image.open(fname).convert("L")
arr = np.asarray(image)
plt.imshow(arr, cmap='gray', vmin=0, vmax=255)
plt.show()
If you want to display the inverse grayscale, switch the cmap to cmap='gray_r'.
如果要显示反灰度，请将cmap切换为cmap='gray_r'。
回答by janneb
Try to use a grayscale colormap?
尝试使用灰度颜色图？
E.g. something like
例如类似的东西
imshow(..., cmap=pyplot.cm.binary)
For a list of colormaps, see http://scipy-cookbook.readthedocs.org/items/Matplotlib_Show_colormaps.html
有关颜色图列表，请参阅http://scipy-cookbook.readthedocs.org/items/Matplotlib_Show_colormaps.html
回答by baco
try this:
尝试这个：
import pylab
from scipy import misc
pylab.imshow(misc.lena(),cmap=pylab.gray())
pylab.show()
回答by Eliel Van Hojman
import matplotlib.pyplot as plt
import matplotlib.pyplot as plt
You can also run once in your code
您也可以在代码中运行一次
plt.gray()
This will show the images in grayscale as default
这将默认以灰度显示图像
im = array(Image.open('I_am_batman.jpg').convert('L'))
plt.imshow(im)
plt.show()
回答by Al Conrad
I would use the get_cmap method. Ex.:
我会使用 get_cmap 方法。前任。：
import matplotlib.pyplot as plt
plt.imshow(matrix, cmap=plt.get_cmap('gray'))
回答by Stanley
@unutbu's answer is quite close to the right answer.
@unutbu 的答案非常接近正确答案。
By default, plt.imshow() will try to scale your (MxN) array data to 0.0~1.0. And then map to 0~255. For most natural taken images, this is fine, you won't see a different. But if you have narrow range of pixel value image, say the min pixel is 156 and the max pixel is 234. The gray image will looks totally wrong. The right way to show an image in gray is
默认情况下，plt.imshow() 会尝试将您的 (MxN) 数组数据缩放到 0.0~1.0。然后映射到0~255。对于大多数自然拍摄的图像，这很好，您不会看到任何不同。但是如果你的像素值范围很窄，比如最小像素为 156，最大像素为 234。灰色图像看起来完全错误。以灰色显示图像的正确方法是
from matplotlib.colors import NoNorm
...
plt.imshow(img,cmap='gray',norm=NoNorm())
...
Let's see an example:
让我们看一个例子：
this is the origianl image: original
这是原始图像：原始图像
this is using defaul norm setting,which is None: wrong pic
这是使用默认规范设置，即无： 错误图片
this is using NoNorm setting,which is NoNorm(): right pic
这是使用 NoNorm 设置，即 NoNorm()： 右图
回答by user3452134
Use no interpolation and set to gray.
不使用插值并设置为灰色。
import matplotlib.pyplot as plt
plt.imshow(img[:,:,1], cmap='gray',interpolation='none')
