Matplotlib: converting a matrix to a raster imageΒΆ

Date:2009-02-26 (last modified), 2006-07-10 (created)

Scipy provides a command (imsave) to make a raster (png, jpg...) image from a 2D array, each pixel corresponding to one value of the array. Yet the image is black and white.

Here is a recipy to do this with Matplotlib, and use a colormap to give color to the image.

In [1]:
from matplotlib.pyplot import *
from scipy import mgrid

def imsave(filename, X, **kwargs):
    """ Homebrewed imsave to have nice colors... """
    figsize=(array(X.shape)/100.0)[::-1]
    rcParams.update({'figure.figsize':figsize})
    fig = figure(figsize=figsize)
    axes([0,0,1,1]) # Make the plot occupy the whole canvas
    axis('off')
    fig.set_size_inches(figsize)
    imshow(X,origin='lower', **kwargs)
    savefig(filename, facecolor='black', edgecolor='black', dpi=100)
    close(fig)


X,Y=mgrid[-5:5:0.1,-5:5:0.1]
Z=sin(X**2+Y**2+1e-4)/(X**2+Y**2+1e-4) # Create the data to be plotted
imsave('imsave.png', Z, cmap=cm.hot )
In [2]:
imshow(imread('imsave.png'))
Out[2]:
<matplotlib.image.AxesImage at 0x7f1733edf610>

Section author: GaelVaroquaux, Unknown[123], Unknown[124]

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