Saving a Numpy array as an image


Question

I have a matrix in the type of a Numpy array. How would I write it to disk it as an image? Any format works (png, jpeg, bmp...). One important constraint is that PIL is not present.

1
224
5/24/2009 10:36:16 AM

Accepted Answer

You can use PyPNG. It's a pure Python (no dependencies) open source PNG encoder/decoder and it supports writing NumPy arrays as images.

53
8/1/2016 11:45:24 AM

This uses PIL, but maybe some might find it useful:

import scipy.misc
scipy.misc.imsave('outfile.jpg', image_array)

EDIT: The current scipy version started to normalize all images so that min(data) become black and max(data) become white. This is unwanted if the data should be exact grey levels or exact RGB channels. The solution:

import scipy.misc
scipy.misc.toimage(image_array, cmin=0.0, cmax=...).save('outfile.jpg')

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