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POSaving a Numpy array as an image (instructions)
 

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  1. POSaving a Numpy array as an image (instructions)
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    <p>I found my answer in a previous post: <a href="https://stackoverflow.com/questions/902761/saving-a-numpy-array-as-an-image">Saving a Numpy array as an image</a>. The only problem being, there isn't much instruction on using the PyPNG module.</p> <p>There are only a few examples online-- <a href="http://packages.python.org/pypng/ex.html#numpy" rel="nofollow noreferrer">http://packages.python.org/pypng/ex.html#numpy</a> <a href="http://nullege.com/codes/search/png.Writer.write" rel="nofollow noreferrer">http://nullege.com/codes/search/png.Writer.write</a></p> <p>But what do I do in light of .write errors like this:</p> <pre><code>Traceback (most recent call last): File "&lt;stdin&gt;", line 1, in &lt;module&gt; File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/png.py", line 638, in write nrows = self.write_passes(outfile, rows) File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/png.py", line 783, in write_passes extend(row) File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/png.py", line 780, in &lt;lambda&gt; return lambda sl: f(map(int, sl)) TypeError: argument 2 to map() must support iteration </code></pre> <p>Here's where the error happens in my code, PCA_tool.py (The error comes after "folder.write(outfilename, PrincipalComponent"):</p> <pre><code>#PrincipalComponent.save(path+'transform_'+str(each)+'.png', format='PNG') outfilename = open(str(path)+'transformed/transform_'+str(each)+'.png', 'wb') folder = png.Writer(m,n,greyscale=True) folder.write(outfilename, PrincipalComponent) outfilename.close() sys.exit(0) </code></pre> <p>I'm trying to save a 8400 element numpy.ndarray as a n=80 column, m=105 row greyscale png image.</p> <p>Thanks,</p>
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    1. COPIL, for all it's problems, is at least more widely used, and therefore a bit better supported. http://www.pythonware.com/products/pil/ You'd probably be better off just doing any rescaling you need to (e.g. rescale and convert to `uint8`) and then `Image.fromarray(data).save('whatever.png')`
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      1. POSaving a Numpy array as an image (instructions)
      1. USJoe Kington
    2. COI should say, PrincipalComponent is of numpy.ndarray type and not a list. I can rescale the array using PrincipalComponent.reshape(row,col), but conversion of a numpy.ndarray into a writable image file?
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    3. COThat's (a `numpy.ndarray`) what `Image.fromarray` expects, for what it's worth.
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      1. POSaving a Numpy array as an image (instructions)
      1. USJoe Kington
 

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