Error saving a numpy.ndarray as an image (.png) using matplotlib.pyplot.imsave

Question

How can I export numpy.ndarray as a graphics file (png, jpg, ...)?

When I try the following:

test = zeros((500, 750, 3), dtype=numpy.uint8)
imsave('out.png',test)

I get this error:

TypeError: from_bounds() takes exactly 4 arguments (5 given)

Below is the complete error output:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-ff0e3e551b72> in <module>()
----> 1 imsave('out.png',test)

/usr/lib/pymodules/python2.7/matplotlib/pyplot.pyc in imsave(*args, **kwargs)
   1751 @docstring.copy_dedent(_imsave)
   1752 def imsave(*args, **kwargs):
-> 1753     return _imsave(*args, **kwargs)
   1754 
   1755 def matshow(A, fignum=None, **kw):

/usr/lib/pymodules/python2.7/matplotlib/image.pyc in imsave(fname, arr, vmin, vmax, cmap, format, origin, dpi)
   1229 
   1230     figsize = [x / float(dpi) for x in arr.shape[::-1]]
-> 1231     fig = Figure(figsize=figsize, dpi=dpi, frameon=False)
   1232     canvas = FigureCanvas(fig)
   1233     im = fig.figimage(arr, cmap=cmap, vmin=vmin, vmax=vmax, origin=origin)

/usr/lib/pymodules/python2.7/matplotlib/figure.pyc in __init__(self, figsize, dpi, facecolor, edgecolor, linewidth, frameon, subplotpars)
    266         self.dpi_scale_trans = Affine2D()
    267         self.dpi = dpi
--> 268         self.bbox_inches = Bbox.from_bounds(0, 0, *figsize)
    269         self.bbox = TransformedBbox(self.bbox_inches, self.dpi_scale_trans)
    270 

TypeError: from_bounds() takes exactly 4 arguments (5 given)

It would help if you showed us where you're importing imsave from — ali_m
– ali_m, Commented Aug 10, 2014 at 14:50
@John Zwinck - you are right. It should have been dtype=numpy.uint8. But even then, imsave does not work. — Martin Vegter
– Martin Vegter, Commented Aug 10, 2014 at 15:01
@ali_m - the function imsave comes from matplotlib.pyplot — Martin Vegter
– Martin Vegter, Commented Aug 10, 2014 at 15:46

ali_m · Accepted Answer · 2014-08-10 16:36:00Z

4

The cause of the error you're seeing is this line in the traceback:

1230     figsize = [x / float(dpi) for x in arr.shape[::-1]]

Your array is 3-dimensional, so figsize will be a list of length 3. Later on, this list gets unpacked in the arguments to Bbox.from_bounds():

--> 268         self.bbox_inches = Bbox.from_bounds(0, 0, *figsize)

Bbox.from_bounds() expects 4 arguments, but since the length of figsize is 3, it will get 5 arguments instead, hence the error.

This bug only affects RGB(A) image arrays, and was fixed in this commit - If you update your version of matplotlib to 1.3.1 or newer, the problem will go away.

Of course, there are lots of other ways to save numpy arrays to image files, and you could always use PIL (as in @enrico.bascis's answer), or one of the other methods from the question that @JohnZwink linked to instead.

edited Aug 10, 2014 at 16:36

answered Aug 10, 2014 at 16:16

ali_m

74.6k28 gold badges230 silver badges314 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

enrico.bacis · Accepted Answer · 2014-08-10 14:52:56Z

3

You can use PIL:

import Image
import numpy as np

test = np.zeros((500, 750, 3), np.int8)
im = Image.fromarray(test, 'RGB')
im.save('test.png')

answered Aug 10, 2014 at 14:52

enrico.bacis

31.9k10 gold badges90 silver badges116 bronze badges

Collectives™ on Stack Overflow

Error saving a numpy.ndarray as an image (.png) using matplotlib.pyplot.imsave

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related