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332 lines
10 KiB
Python
332 lines
10 KiB
Python
#!/usr/bin/env python2
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# -*- coding: utf-8 -*-
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#
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# © 2013-14: jbarlow83 from Github (https://github.com/jbarlow83)
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#
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#
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# Use Leptonica to detect find and remove page skew. Leptonica uses the method
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# of differential square sums, which its author claim is faster and more robust
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# than the Hough transform used by ImageMagick.
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from __future__ import print_function, absolute_import, division
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import argparse
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import ctypes as C
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import sys
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import os
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import logging
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from tempfile import TemporaryFile
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logger = logging.getLogger(__name__)
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def stderr(*objs):
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"""Python 2/3 compatible print to stderr.
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"""
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print("leptonica.py:", *objs, file=sys.stderr)
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from ctypes.util import find_library
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lept_lib = find_library('lept')
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if not lept_lib:
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stderr("Could not find the Leptonica library")
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sys.exit(3)
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try:
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lept = C.cdll.LoadLibrary(lept_lib)
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except Exception:
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stderr("Could not load the Leptonica library from %s", lept_lib)
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sys.exit(3)
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class _PIXCOLORMAP(C.Structure):
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"""struct PixColormap from Leptonica src/pix.h
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"""
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_fields_ = [
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("array", C.c_void_p),
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("depth", C.c_int32),
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("nalloc", C.c_int32),
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("n", C.c_int32)
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]
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class _PIX(C.Structure):
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"""struct Pix from Leptonica src/pix.h
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"""
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_fields_ = [
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("w", C.c_uint32),
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("h", C.c_uint32),
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("d", C.c_uint32),
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("wpl", C.c_uint32),
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("refcount", C.c_uint32),
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("xres", C.c_int32),
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("yres", C.c_int32),
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("informat", C.c_int32),
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("text", C.POINTER(C.c_char)),
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("colormap", C.POINTER(_PIXCOLORMAP)),
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("data", C.POINTER(C.c_uint32))
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]
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PIX = C.POINTER(_PIX)
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lept.pixRead.argtypes = [C.c_char_p]
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lept.pixRead.restype = PIX
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lept.pixScale.argtypes = [PIX, C.c_float, C.c_float]
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lept.pixScale.restype = PIX
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lept.pixDeskew.argtypes = [PIX, C.c_int32]
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lept.pixDeskew.restype = PIX
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lept.pixFindSkew.argtypes = [PIX, C.POINTER(C.c_float), C.POINTER(C.c_float)]
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lept.pixFindSkew.restype = C.c_int32
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lept.pixWriteImpliedFormat.argtypes = [C.c_char_p, PIX, C.c_int32, C.c_int32]
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lept.pixWriteImpliedFormat.restype = C.c_int32
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lept.pixDestroy.argtypes = [C.POINTER(PIX)]
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lept.pixDestroy.restype = None
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lept.getLeptonicaVersion.argtypes = []
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lept.getLeptonicaVersion.restype = C.c_char_p
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class LeptonicaErrorTrap(object):
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"""Context manager to trap errors reported by Leptonica.
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Leptonica's error return codes are unreliable to the point of being
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almost useless. It does, however, write errors to stderr provided that is
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not disabled at its compile time. Fortunately this is done using error
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macros so it is very self-consistent.
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This context manager redirects stderr to a temporary file which is then
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read and parsed for error messages. As a side benefit, debug messages
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from Leptonica are also suppressed.
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"""
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def __enter__(self):
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self.tmpfile = TemporaryFile()
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# Save the old stderr, and redirect stderr to temporary file
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self.old_stderr_fileno = os.dup(sys.stderr.fileno())
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os.dup2(self.tmpfile.fileno(), sys.stderr.fileno())
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return
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def __exit__(self, exc_type, exc_value, traceback):
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# Restore old stderr
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os.dup2(self.old_stderr_fileno, sys.stderr.fileno())
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# Get data from tmpfile (in with block to ensure it is closed)
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with self.tmpfile as tmpfile:
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tmpfile.seek(0) # Cursor will be at end, so move back to beginning
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leptonica_output = tmpfile.read().decode(errors='replace')
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# If there are Python errors, let them bubble up
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if exc_type:
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logger.warning(leptonica_output)
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return False
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# If there are Leptonica errors, wrap them in Python excpetions
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if 'Error' in leptonica_output:
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if 'image file not found' in leptonica_output:
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raise FileNotFoundError()
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if 'pixWrite: stream not opened' in leptonica_output:
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raise LeptonicaIOError()
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raise LeptonicaError(leptonica_output)
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return False
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class LeptonicaError(Exception):
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pass
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class LeptonicaIOError(LeptonicaError):
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pass
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def pixRead(filename):
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"""Load an image file into a PIX object.
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Leptonica can load TIFF, PNM (PBM, PGM, PPM), PNG, and JPEG. If loading
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fails then the object will wrap a C null pointer.
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"""
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with LeptonicaErrorTrap():
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return lept.pixRead(filename.encode(sys.getfilesystemencoding()))
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def pixScale(pix, scalex, scaley):
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"""Returns the pix object rescaled according to the proportions given."""
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with LeptonicaErrorTrap():
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return lept.pixScale(pix, scalex, scaley)
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def pixDeskew(pix, reduction_factor=0):
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"""Returns the deskewed pix object.
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A clone of the original is returned when the algorithm cannot find a skew
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angle with sufficient confidence.
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reduction_factor -- amount to downsample (0 for default) when searching
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for skew angle
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"""
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with LeptonicaErrorTrap():
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return lept.pixDeskew(pix, reduction_factor)
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def pixFindSkew(pix):
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"""Returns a tuple (deskew angle in degrees, confidence value).
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Returns (None, None) if no angle is available.
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"""
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with LeptonicaErrorTrap():
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angle = C.c_float(0.0)
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confidence = C.c_float(0.0)
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result = lept.pixFindSkew(pix, C.byref(angle), C.byref(confidence))
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if result == 0:
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return (angle.value, confidence.value)
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else:
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return (None, None)
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def pixWriteImpliedFormat(filename, pix, jpeg_quality=0, jpeg_progressive=0):
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"""Write pix to the filename, with the extension indicating format.
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jpeg_quality -- quality (iff JPEG; 1 - 100, 0 for default)
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jpeg_progressive -- (iff JPEG; 0 for baseline seq., 1 for progressive)
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"""
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fileroot, extension = os.path.splitext(filename)
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fix_pnm = False
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if extension.lower() in ('.pbm', '.pgm', '.ppm'):
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# Leptonica does not process handle these extensions correctly, but
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# does handle .pnm correctly. Add another .pnm suffix.
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filename += '.pnm'
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fix_pnm = True
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with LeptonicaErrorTrap():
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lept.pixWriteImpliedFormat(
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filename.encode(sys.getfilesystemencoding()),
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pix, jpeg_quality, jpeg_progressive)
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if fix_pnm:
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from shutil import move
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move(filename, filename[:-4]) # Remove .pnm suffix
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def pixDestroy(pix):
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"""Destroy the pix object.
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Function signature is pixDestroy(struct Pix **), hence C.byref() to pass
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the address of the pointer.
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"""
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with LeptonicaErrorTrap():
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lept.pixDestroy(C.byref(pix))
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def getLeptonicaVersion():
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"""Get Leptonica version string.
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Caveat: Leptonica expects the caller to free this memory. We don't,
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since that would involve binding to libc to access libc.free(),
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a pointless effort to reclaim 100 bytes of memory.
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"""
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return lept.getLeptonicaVersion().decode()
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def deskew(infile, outfile, dpi):
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try:
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pix_source = pixRead(infile)
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except LeptonicaIOError:
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raise LeptonicaIOError("Failed to open file: %s" % infile)
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if dpi < 150:
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reduction_factor = 1 # Don't downsample too much if DPI is already low
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else:
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reduction_factor = 0 # Use default
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pix_deskewed = pixDeskew(pix_source, reduction_factor)
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try:
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pixWriteImpliedFormat(outfile, pix_deskewed)
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except LeptonicaIOError:
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raise LeptonicaIOError("Failed to open destination file: %s" % outfile)
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pixDestroy(pix_source)
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pixDestroy(pix_deskewed)
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if __name__ == '__main__':
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parser = argparse.ArgumentParser(
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description="Python wrapper to access Leptonica")
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subparsers = parser.add_subparsers(title='commands',
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description='supported operations')
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parser_deskew = subparsers.add_parser('deskew')
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parser_deskew.add_argument('-r', '--dpi', dest='dpi', action='store',
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type=int, default=300, help='input resolution')
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parser_deskew.add_argument('infile', help='image to deskew')
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parser_deskew.add_argument('outfile', help='deskewed output image')
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parser_deskew.set_defaults(func=deskew)
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args = parser.parse_args()
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if getLeptonicaVersion() != u'leptonica-1.69':
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print("Unexpected leptonica version: %s" % getLeptonicaVersion())
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args.func(args)
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def _test_output(mode, extension, im_format):
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from PIL import Image
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from tempfile import NamedTemporaryFile
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with NamedTemporaryFile(prefix='test-lept-pnm', suffix=extension, delete=True) as tmpfile:
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im = Image.new(mode=mode, size=(100, 100))
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im.save(tmpfile)
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pix = pixRead(tmpfile.name)
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pixWriteImpliedFormat(tmpfile.name, pix)
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pixDestroy(pix)
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im_roundtrip = Image.open(tmpfile.name)
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assert im_roundtrip.mode == im.mode, "leptonica mode differs"
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assert im_roundtrip.format == im_format, \
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"{0}: leptonica produced a {1}".format(
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extension,
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im_roundtrip.format)
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def test_pnm_output():
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params = [['1', '.pbm', 'PPM'], ['L', '.pgm', 'PPM'],
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['RGB', '.ppm', 'PPM']]
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for param in params:
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_test_output(*param)
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def test_skew_angle():
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from PIL import Image, ImageDraw
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from tempfile import NamedTemporaryFile
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im = Image.new(mode='1', size=(1000, 1000), color=1)
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draw = ImageDraw.Draw(im)
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for n in range(20):
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draw.line([(50, 25 + 50*n), (950, 25 + 50*n)], width=1)
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del draw
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test_angles = [0.1 * ang for ang in range(1, 10)] + \
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[float(ang) for ang in range(1, 7)]
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test_angles += [-ang for ang in test_angles]
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test_angles = sorted(test_angles)
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for rotate_angle in test_angles:
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rotated_im = im.rotate(rotate_angle)
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with NamedTemporaryFile(prefix='lept-skew', suffix='.png', delete=True) as tmpfile:
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rotated_im.save(tmpfile)
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pix = pixRead(tmpfile.name)
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angle, confidence = pixFindSkew(pix)
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pixDestroy(pix)
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print('{0} {1} {2}'.format(rotate_angle, angle, confidence), file=sys.stderr)
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