Currently imsave (implemented in the image.py file) only deals with
greyscale single-plane images, i.e. 2D arrays, and in my defence, it's
in the docstring, so I wouldn't call it a bug. However, it's a
reasonable expectation that it support rgb and rgba since it is
basically a thin wrapper around figimage.
My first try at this was to change the line
fig = Figure(figsize=arr.shape[::-1], dpi=1, frameon=False)
to
fig = Figure(figsize=(arr.shape[1],arr.shape[0]), dpi=1, frameon=False)
since we just want to take the first two shape values.
(note figsize=arr.shape[:2][::-1] also works)
This may be all you need. My tests (in the attached test.py) appear to
work. However, I don't think it's what you want. By default, figimage
even expects NxMx3 and NxMx4 arrays to be float arrays nominally ranging
from 0-1. What you probably want is a raw RGB mapping where pixel planes
are unsigned 8 bit values. I thought calling figimage with a
norm=no_norm(0,255) instance achieved this but it doesn't work as I
expect. So the first question is, what is the expected behaviour here,
and a follow-up is does anyone here understand how to do the colour
mapping to achieve it?
Gary
Stéfan van der Walt wrote:
Hey all,
2009/2/10 Andrew Straw <straw...@astraw.com>:
Gary Ruben wrote:
Hi Andrew,
I don't have commit access. If you would check it in, that would be great.
Committed to the trunk in r6899... Thanks!
And, sheesh, SourceForge's SVN server is slooow today for me, although
it seems to have finally improved.
While trying to write a matplotlib plugin for scikits.image, we
noticed that `imsave` isn't currently working (that goes for the one
in Ubuntu [0.99 I think] as well as the latest SVN):
Traceback (most recent call last):
File "test_imsave.py", line 6, in <module>
plt.imsave('test.jpg', img)
File "/Users/stefan/lib/python2.6/site-packages/matplotlib/pyplot.py",
line 1412, in imsave
return _imsave(*args, **kwargs)
File "/Users/stefan/lib/python2.6/site-packages/matplotlib/image.py",
line 1025, in imsave
fig = Figure(figsize=arr.shape[::-1], dpi=1, frameon=False)
File "/Users/stefan/lib/python2.6/site-packages/matplotlib/figure.py",
line 180, in __init__
self.bbox_inches = Bbox.from_bounds(0, 0, *figsize)
TypeError: from_bounds() takes exactly 4 arguments (5 given)
The commands needed to reproduce the error are:
import matplotlib.pyplot as plt
import numpy as np
img = np.ones((50, 50, 3), dtype=np.uint8)
plt.imsave('test.jpg', img)
Regards
Stéfan
def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
origin=None):
"""
Saves a 2D :class:`numpy.array` as an image with one pixel per element.
The output formats available depend on the backend being used.
Arguments:
*fname*:
A string containing a path to a filename, or a Python file-like object.
If *format* is *None* and *fname* is a string, the output
format is deduced from the extension of the filename.
*arr*:
A 2D array.
Keyword arguments:
*vmin*/*vmax*: [ None | scalar ]
*vmin* and *vmax* set the color scaling for the image by fixing the
values that map to the colormap color limits. If either *vmin* or *vmax*
is None, that limit is determined from the *arr* min/max value.
*cmap*:
cmap is a colors.Colormap instance, eg cm.jet.
If None, default to the rc image.cmap value.
*format*:
One of the file extensions supported by the active
backend. Most backends support png, pdf, ps, eps and svg.
*origin*
[ 'upper' | 'lower' ] Indicates where the [0,0] index of
the array is in the upper left or lower left corner of
the axes. Defaults to the rc image.origin value.
"""
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure
fig = Figure(figsize=arr.shape[::-1], dpi=1, frameon=False)
canvas = FigureCanvas(fig)
fig.figimage(arr, cmap=cmap, vmin=vmin, vmax=vmax, origin=origin)
fig.savefig(fname, dpi=1, format=format)
def newimsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
origin=None):
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure
fig = Figure(figsize=arr.shape[:2][::-1], dpi=1, frameon=False)
canvas = FigureCanvas(fig)
fig.figimage(arr, cmap=cmap, vmin=vmin, vmax=vmax, origin=origin)
fig.savefig(fname, dpi=1, format=format)
import numpy as np
import matplotlib.pyplot as plt
from my_plottools import newimsave
arr = np.empty((20,20,3),dtype=np.uint16)
arr[...,0] = np.tri(20)*255/3
arr[...,1] = arr[:,::-1,0]
arr[...,2] = arr[::-1,:,0]
newimsave(r'd:\temp\test1.png', arr)
arr = np.empty((20,30,3),dtype=np.uint16)
arr[...,0] = np.outer(np.linspace(0,255,20), np.ones(30))
arr[...,1] = np.outer(np.ones(20), np.linspace(0,255,30))
arr[...,2] = np.outer(np.linspace(0,np.sqrt(255),20),
np.linspace(0,np.sqrt(255),30))
# arr[...,3] = np.mgrid[0,0:255:20]
newimsave(r'd:\temp\test2.png', arr)
arr = np.empty((20,30,4),dtype=np.uint16)
arr[...,0] = np.outer(np.linspace(0,255,20), np.ones(30))
arr[...,1] = np.outer(np.ones(20), np.linspace(0,255,30))
arr[...,2] = np.outer(np.linspace(0,np.sqrt(255),20),
np.linspace(0,np.sqrt(255),30))
arr[...,3] = np.outer(np.linspace(0,255,20),
np.hstack((np.zeros(15),np.ones(15))))
newimsave(r'd:\temp\test3.png', arr)
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