336 lines
11 KiB
Python
336 lines
11 KiB
Python
#!/usr/bin/env python2
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# -*- coding: utf-8 -*-
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#
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# © 2013-15: 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 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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from ctypes.util import find_library
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from .lib._leptonica import ffi
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from functools import lru_cache
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lept = ffi.dlopen(find_library('lept'))
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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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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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class Pix:
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"""Wrapper around leptonica's PIX object.
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Leptonica uses referencing counting on PIX objects. Also, many Leptonica
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functions return the original object with an increased reference count
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if the operation had no effect (for example, image skew was found to be 0).
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This has complications for memory management in Python. Whenever Leptonica
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returns a PIX object (new or old), we wrap it in this class, which
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registers it with the FFI garbage collector. pixDestroy() decrements the
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reference count and only destroys when the last reference is removed.
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Leptonica's reference counting is not threadsafe. This class can be used
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in a threadsafe manner if a Python threading.Lock protects the data.
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"""
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def __init__(self, cpix):
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self.cpix = ffi.gc(cpix, Pix._pix_destroy)
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def __repr__(self):
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if self.cpix:
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s = "<leptonica.Pix image size={0}x{1} depth={2} at 0x{3:x}>"
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return s.format(self.cpix.w, self.cpix.h, self.cpix.d,
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int(ffi.cast("intptr_t", self.cpix)))
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else:
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return "<leptonica.Pix image NULL>"
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def __getstate__(self):
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data = ffi.new('l_uint32 **')
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size = ffi.new('size_t *')
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err = lept.pixSerializeToMemory(self.cpix, data, size)
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if err != 0:
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raise LeptonicaIOError("pixSerializeToMemory")
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char_data = ffi.cast('char *', data[0])
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data_bytes = ffi.buffer(char_data, size[0])[:]
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lept.lept_free(char_data)
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return dict(data=data_bytes)
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def __setstate__(self, state):
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cdata_bytes = ffi.new('char[]', state['data'])
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cdata_uint32 = ffi.cast('l_uint32 *', cdata_bytes)
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self.cpix = lept.pixDeserializeFromMemory(
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cdata_uint32, len(state['data']))
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@property
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def width(self):
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return self.cpix.w
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@property
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def height(self):
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return self.cpix.h
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@classmethod
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def read(cls, 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
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loading 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 cls(lept.pixRead(
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filename.encode(sys.getfilesystemencoding())))
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def write_implied_format(
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self, filename, 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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with LeptonicaErrorTrap():
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lept.pixWriteImpliedFormat(
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filename.encode(sys.getfilesystemencoding()),
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self.cpix, jpeg_quality, jpeg_progressive)
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def deskew(self, 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
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skew 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 Pix(lept.pixDeskew(self.cpix, reduction_factor))
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def scale(self, 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 Pix(lept.pixScale(self.cpix, scalex, scaley))
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def rotate180(self):
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with LeptonicaErrorTrap():
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return Pix(lept.pixRotate180(ffi.NULL, self.cpix))
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def find_skew(self):
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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 = ffi.new('float *', 0.0)
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confidence = ffi.new('float *', 0.0)
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result = lept.pixFindSkew(self.cpix, angle, confidence)
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if result == 0:
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return (angle[0], confidence[0])
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else:
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return (None, None)
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def otsu_adaptive_threshold(
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self, tile_size=(300, 300), kernel_size=(4, 4), scorefract=0.1):
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with LeptonicaErrorTrap():
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sx, sy = tile_size
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smoothx, smoothy = kernel_size
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p_cpix = ffi.new('PIX **')
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result = lept.pixOtsuAdaptiveThreshold(
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self.cpix,
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sx, sy,
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smoothx, smoothy,
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scorefract,
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ffi.NULL,
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p_cpix)
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if result == 0:
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return Pix(p_cpix[0])
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else:
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return None
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@staticmethod
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@lru_cache(maxsize=1)
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def make_pixel_sum_tab8():
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return lept.makePixelSumTab8()
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@staticmethod
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def correlation_binary(pix1, pix2):
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if get_leptonica_version() < 'leptonica-1.72':
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# Older versions of Leptonica (pre-1.72) have a buggy
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# implementation of pixCorrelationBinary that overflows on larger
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# images.
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pix1_count = ffi.new('l_int32 *')
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pix2_count = ffi.new('l_int32 *')
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pixn_count = ffi.new('l_int32 *')
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tab8 = Pix.make_pixel_sum_tab8()
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lept.pixCountPixels(pix1.cpix, pix1_count, tab8)
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lept.pixCountPixels(pix2.cpix, pix2_count, tab8)
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pixn = Pix(lept.pixAnd(ffi.NULL, pix1.cpix, pix2.cpix))
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lept.pixCountPixels(pixn.cpix, pixn_count, tab8)
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# Python converts these int32s to larger units as needed
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# to avoid overflow. Overflow happens easily here.
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correlation = (
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(pixn_count[0] * pixn_count[0]) /
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(pix1_count[0] * pix2_count[0])
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)
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return correlation
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else:
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correlation = ffi.new('float *', 0.0)
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result = lept.pixCorrelationBinary(pix1.cpix, pix2.cpix,
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correlation)
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if result != 0:
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raise LeptonicaError("Correlation failed")
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return correlation[0]
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@staticmethod
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def _pix_destroy(pix):
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ptr_to_pix = ffi.new('PIX **', pix)
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lept.pixDestroy(ptr_to_pix)
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# print('pix destroy ' + repr(pix))
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@lru_cache(maxsize=1)
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def get_leptonica_version():
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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 ffi.string(lept.getLeptonicaVersion()).decode()
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def deskew(infile, outfile, dpi):
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try:
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pix_source = Pix.read(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 = pix_source.deskew(reduction_factor)
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try:
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pix_deskewed.write_implied_format(outfile)
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except LeptonicaIOError:
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raise LeptonicaIOError("Failed to open destination file: %s" % outfile)
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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 get_leptonica_version() != 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_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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print('{0} {1} {2}'.format(rotate_angle, angle, confidence), file=sys.stderr)
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