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POHow to write PIL image filter for plain pgm format?
 

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  1. POHow to write PIL image filter for plain pgm format?
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    <p>How can I write a filter for python imaging library for pgm plain ascii format (P2). Problem here is that basic PIL filter assumes constant number of bytes per pixel. </p> <p>My goal is to open feep.pgm with Image.open(). See <a href="http://netpbm.sourceforge.net/doc/pgm.html" rel="nofollow">http://netpbm.sourceforge.net/doc/pgm.html</a> or below.</p> <p>Alternative solution is that I find other well documented ascii grayscale format that is supported by PIL and all major graphics programs. Any suggestions?</p> <p>feep.pgm:</p> <pre><code>P2 # feep.pgm 24 7 15 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0 0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0 0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0 0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0 0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 </code></pre> <p><strong>edit:</strong> Thanks for the answer, It works... <strong>but</strong> I need a solution that uses Image.open(). Most of python programs out there use PIL for graphics manipulation (google: python image open). Thus, I need to be able to register a filter to PIL. Then, I can use any software that uses PIL. I now think mostly scipy, pylab, etc. dependent programs.</p> <p><strong>edit</strong> Ok, I think I got it now. Below is the wrapper pgm2pil.py:</p> <pre><code>import Image import numpy def pgm2pil(filename): try: inFile = open(filename) header = None size = None maxGray = None data = [] for line in inFile: stripped = line.strip() if stripped[0] == '#': continue elif header == None: if stripped != 'P2': return None header = stripped elif size == None: size = map(int, stripped.split()) elif maxGray == None: maxGray = int(stripped) else: for item in stripped.split(): data.append(int(item.strip())) data = numpy.reshape(data, (size[1],size[0]))/float(maxGray)*255 return numpy.flipud(data) except: pass return None def imageOpenWrapper(fname): pgm = pgm2pil(fname) if pgm is not None: return Image.fromarray(pgm) return origImageOpen(fname) origImageOpen = Image.open Image.open = imageOpenWrapper </code></pre> <p>There is a slight upgrade to misha's answer. Image.open has to be saved in order to prevent never ending loops. If pgm2pil returns None wrapper calls pgm2pil which returns None which calls pgm2pil...</p> <p>Below is the test function (feep_false.pgm is a malformed pgm e.g. "P2" -> "FOO" and lena.pgm is just <strong>the</strong> image file):</p> <pre><code>import pgm2pil import pylab try: pylab.imread('feep_false.pgm') except IOError: pass else: raise ValueError("feep_false should fail") pylab.subplot(2,1,1) a = pylab.imread('feep.pgm') pylab.imshow(a) pylab.subplot(2,1,2) b = pylab.imread('lena.png') pylab.imshow(b) pylab.show() </code></pre>
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