Display image as grayscale using matplotlib

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convert numpy array to grayscale

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.

I read in the image and convert to grayscale using PIL's Image.open().convert("L")

image = Image.open(file).convert("L")

Then I convert the image to a matrix so that I can easily do some image processing using

matrix = scipy.misc.fromimage(image, 0)

However, when I do

figure()  
matplotlib.pyplot.imshow(matrix)  
show()

it displays the image using a colormap (i.e. it's not grayscale).

What am I doing wrong here?

The following code will load an image from a file image.png and will display it as grayscale.

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'.

Display image as grayscale using matplotlib, Note: For actually displaying a grayscale image set up the color mapping using the parameters cmap='gray', vmin=0, vmax=255 . Answers: The following code will load an image from a file image.png and will display it as grayscale. 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') plt.show ()

Try to use a grayscale colormap?

E.g. something like

imshow(..., cmap=pyplot.cm.binary)

For a list of colormaps, see http://scipy-cookbook.readthedocs.org/items/Matplotlib_Show_colormaps.html

matplotlib.pyplot.imshow, To convert an image to grayscale using python, a solution is to use PIL example: How to from PIL import Image img = Image.open('lena.png').convert('LA') Display image as grayscale using matplotlib, stackoverflow  In the case you want a color image transformed and displayed in grayscale: import matplotlib as plt # Reading color image as grayscale img = cv2.imread(path, 0) plt.imshow(img, cmap='gray') plt.show() where path is file location. Another method is to the conversion by yourself. The filter you then should use is as follows:

import matplotlib.pyplot as plt

You can also run once in your code

plt.gray()

This will show the images in grayscale as default

im = array(Image.open('I_am_batman.jpg').convert('L'))
plt.imshow(im)
plt.show()

How to convert an image to grayscale using python ?, Generally, users would like to show the gray image with true pixel value, so why not default vmin and vmax to the above number in cmap='gray'  The basic steps you need to do are to transform from the RGB colorspace to a colorspace that encodes with something approximating the luma/chroma model, such as YUV/YIQ or HSL/HSV, then slice off the luma-like channel and use that as your greyscale image. matplotlib does not appear to provide a mechanism to convert to YUV/YIQ, but it does let you convert to HSV.

I would use the get_cmap method. Ex.:

import matplotlib.pyplot as plt

plt.imshow(matrix, cmap=plt.get_cmap('gray'))

Why does pyplot display wrong grayscale image? · Issue #7221 , Hello guys, Now I used PIL to convert my image from RGB to Grayscale, and then I use the matplotlib to show the coordinate value and  Using Matplotlib, with just a few lines of code we can easily display an image in Python. Display image using Matplotlib in python. Now let’s jump into the code without wasting time anymore: At the very beginning, first import our Matplotlib library and the Matplotlib image sub-package:

@unutbu's answer is quite close to the right answer.

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

from matplotlib.colors import NoNorm
...
plt.imshow(img,cmap='gray',norm=NoNorm())
...

Let's see an example:

this is the origianl image: original

this is using defaul norm setting,which is None: wrong pic

this is using NoNorm setting,which is NoNorm(): right pic

show grayscale image using matplotlib, 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  Display data as an image; i.e. on a 2D regular raster. The input may either be actual RGB (A) data, or 2D scalar data, which will be rendered as a pseudocolor image. Note: For actually displaying a grayscale image set up the color mapping using the parameters cmap='gray', vmin=0, vmax=255.

Display image as grayscale using matplotlib, You need to set the cmap properties of the imshow() function: https://matplotlib.​org/devdocs/api/_as_gen/matplotlib.pyplot.imshow.html. Use:. Use the function cv.imshow () to display an image in a window. The window automatically fits to the image size. First argument is a window name which is a string. Second argument is our image.

Convert RGB Image to Grayscale and Display It (Python + Matplotlib , im = array(Image.open('I_am_batman.jpg').convert('L')) plt.imshow(im) plt.show() import matplotlib.pyplot as plt plt.gray(). This will show the images in grayscale  If you are using matplotlib and want to show the image in your interactive notebook, try the following: %pylab inline import matplotlib.pyplot as plt import matplotlib.image as mpimg img=mpimg.imread('your_image.png') imgplot = plt.imshow(img) plt.show()

python Display image as grayscale using matplotlib?, This question already has an answer here: Display image as grayscale using matplotlib 7 answers I see an oddness when loading an image using opencv,  But they are consistent in that no matter its shape, the input is by default rendered as a natural image, i.e. using grayscale colormap with 0..255 or 0..1 value range in case of 2D. Matplotlib's imshow , on the other hand, kind of feels like a wrapper around two functionalities with different purpose: imshow and imagesc / pcolor .

Comments
  • @jay: Per this doc string, "Note that any colormap listed here can be reversed by appending _r."
  • Warning matplotlib adjust pixel scale intensity if you do not want use: plt.imshow(im_gray,cmap='gray', vmin = 0, vmax = 255)
  • Which library are you using for gray() or grey() ?
  • @SherylHohman, it is gray... gray is standard American spelling and grey is British spelling for the same color.
  • there is no pylab.grey(), maybe it has been removed?