Save matplotlib plot in grayscale


Question

I have some color plots that I need to be saved in grayscale. Is there an easy way to do this without changing the plotting formats?

1
18
5/16/2011 3:15:56 PM

Accepted Answer

Actually, this was asked before. Here is a pretty good answer, which comes 2nd on google (as of today):
Display image as grayscale using matplotlib

And the solution is VERY similar to Suki's...

Oh, well, I am bored, so I post here also a full blown code:

import numpy as np
import pylab as p
xv=np.ones(4)*.5
yv=np.arange(0,4,1)
xv1=np.ones(4)*-.5
yv1=np.arange(0,4,1)

#red vertical line on the right
yv2=np.arange(0,1.5,0.1)
xv2=np.ones_like(yv2)*.7

#red vertical line on the left
yv3=np.arange(0,2,0.01)
xv3=np.ones_like(yv3)*-0.7

###
xc=np.arange(-1.4,2,0.05)
yc=np.ones_like(xc)*1

fig = p.figure()
ax1 = fig.add_subplot(111)
#adjustprops = dict(left=0.12, bottom=0.2, right=0.965, top=0.96, wspace=0.13, hspace=0.37)
#fig.subplots_adjust(**adjustprops)
ax1.plot(xv,yv, color='blue', lw=1, linestyle='dashed')
ax1.plot(xv1,yv1, 'green', linestyle='dashed')
ax1.plot(np.r_[-1:1:0.2],np.r_[-1:1:0.2],'red')
ax1.plot(xc,yc, 'k.', markersize=3)

p.savefig('colored_image.png')

import matplotlib.image as mpimg
import matplotlib.cm as cm
import Image

figprops = dict(figsize=(10,10), dpi=100)
fig1 = p.figure(**figprops)
#fig1 = p.figure()
#ax1 = fig.add_subplot(111)
adjustprops = dict()
image=Image.open('colored_image.png').convert("L")
arr=np.asarray(image)
p.figimage(arr,cmap=cm.Greys_r)
p.savefig('grayed.png')
p.savefig('grayed.pdf',papertype='a4',orientation='portrait')

This will produce a graph in color, than read it, convert it to gray scale, and will save a png and pdf.

5
8/21/2017 4:38:12 PM

It's currently awkward to do directly from matplotlib, but in "the future" they plan to support a set_gray(True) call on the figure (see the mailing list thread here).

Your best options will be to save it in color and convert it, either in python with PIL:

import Image
Image.open('color.png').convert('L').save('bw.png')

or from the command line with imagemagick:

convert -type Grayscale color.png bw.png

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