James R. Barlow
a45505cf1d
Issue #73. The order of operations happens to not matter for scaling but does matter for translation. We only need scaling to find the DPI, so the error was not noticed. Mainly useful to other uses of this library.
336 lines
11 KiB
Python
336 lines
11 KiB
Python
#!/usr/bin/env python3
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# © 2015 James R. Barlow: github.com/jbarlow83
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from subprocess import Popen, PIPE
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from decimal import Decimal, getcontext
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from math import hypot
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import re
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import sys
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import PyPDF2 as pypdf
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from collections import namedtuple
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matrix_mult = pypdf.pdf.utils.matrixMultiply
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FRIENDLY_COLORSPACE = {
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'/DeviceGray': 'gray',
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'/CalGray': 'gray',
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'/DeviceRGB': 'rgb',
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'/CalRGB': 'rgb',
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'/DeviceCMYK': 'cmyk',
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'/Lab': 'lab',
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'/ICCBased': 'icc',
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'/Indexed': 'index',
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'/Separation': 'sep',
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'/DeviceN': 'devn',
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'/Pattern': '-',
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'/G': 'gray', # Abbreviations permitted in inline images
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'/RGB': 'rgb',
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'/CMYK': 'cmyk',
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'/I': 'index',
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}
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FRIENDLY_ENCODING = {
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'/CCITTFaxDecode': 'ccitt',
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'/DCTDecode': 'jpeg',
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'/JPXDecode': 'jpx',
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'/JBIG2Decode': 'jbig2',
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'/CCF': 'ccitt', # Abbreviations permitted in inline images
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'/DCT': 'jpeg',
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'/AHx': 'asciihex',
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'/A85': 'ascii85',
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'/LZW': 'lzw',
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'/Fl': 'flate',
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'/RL': 'runlength'
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}
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FRIENDLY_COMP = {
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'gray': 1,
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'rgb': 3,
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'cmyk': 4,
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'lab': 3,
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'index': 1
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}
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def _matrix_from_shorthand(shorthand):
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"""Convert from PDF matrix shorthand to full matrix
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PDF 1.7 spec defines a shorthand for describing the entries of a matrix
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since the last column is always (0, 0, 1).
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"""
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a, b, c, d, e, f = map(float, shorthand)
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return ((a, b, 0),
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(c, d, 0),
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(e, f, 1))
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def _shorthand_from_matrix(matrix):
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"""Convert from transformation matrix to PDF shorthand."""
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a, b = matrix[0][0], matrix[0][1]
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c, d = matrix[1][0], matrix[1][1]
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e, f = matrix[2][0], matrix[2][1]
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return tuple(map(float, (a, b, c, d, e, f)))
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ContentsInfo = namedtuple('ContentsInfo', ['raster_settings', 'inline_images'])
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def _interpret_contents(contentstream):
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operations = contentstream.operations
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stack = []
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ctm = _matrix_from_shorthand((1, 0, 0, 1, 0, 0))
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image_raster_settings = []
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inline_images = []
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for op in operations:
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operands, command = op
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if command == b'q':
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stack.append(ctm)
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if len(stack) > 32:
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raise RuntimeError("PDF graphics stack overflow")
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elif command == b'Q':
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ctm = stack.pop()
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elif command == b'cm':
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ctm = matrix_mult(
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_matrix_from_shorthand(operands), ctm)
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elif command == b'Do':
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image_name = operands[0]
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image_raster_settings.append(
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(image_name, _shorthand_from_matrix(ctm)))
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elif command == b'INLINE IMAGE':
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settings = operands['settings']
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inline_images.append(
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(settings, _shorthand_from_matrix(ctm)))
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return ContentsInfo(
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raster_settings=image_raster_settings,
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inline_images=inline_images)
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def _get_dpi(ctm_shorthand, image_size):
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"""Given the transformation matrix and image size, find the image DPI.
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PDFs do not include image resolution information within image data.
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Instead, the PDF page content stream describes the location where the
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image will be rasterized, and the effective resolution is the ratio of the
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pixel size to raster target size.
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Normally a scanned PDF has the paper size set appropriately but this is
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not guaranteed. The most common case is a cropped image will change the
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page size (/CropBox) without altering the page content stream. That means
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it is not sufficient to assume that the image fills the page, even though
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that is the most common case.
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A PDF image may be scaled (always), cropped, translated, rotated in place
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to an arbitrary angle (rarely) and skewed. Only equal area mappings can
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be expressed, that is, it is not necessary to consider distortions where
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the effective DPI varies with position.
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To determine the image scale, transform an offset axis vector v0 (0, 0),
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width-axis vector v0 (1, 0), height-axis vector vh (0, 1) with the matrix,
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which gives the dimensions of the image in PDF units. From there we can
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compare to actual image dimensions. PDF uses
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row vector * matrix_tranposed unlike the traditional
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matrix * column vector.
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The offset, width and height vectors can be combined in a matrix and
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multiplied by the transform matrix. Then we want to calculated
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magnitude(width_vector - offset_vector)
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and
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magnitude(height_vector - offset_vector)
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When the above is worked out algebraically, the effect of translation
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cancels out, and the vector magnitudes become functions of the nonzero
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transformation matrix indices. The results of the derivation are used
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in this code.
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pdfimages -list does calculate the DPI in some way that is not completely
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naive, but it does not get the DPI of rotated images right, so cannot be
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used anymore to validate this. Photoshop works, or using Acrobat to
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rotate the image back to normal.
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It does not matter if the image is partially cropped, or even out of the
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/MediaBox.
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"""
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a, b, c, d, _, _ = ctm_shorthand
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# Calculate the width and height of the image in PDF units
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image_drawn_width = hypot(a, b)
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image_drawn_height = hypot(c, d)
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# The scale of the image is pixels per PDF unit (1/72")
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scale_w = image_size[0] / image_drawn_width
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scale_h = image_size[1] / image_drawn_height
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# DPI = scale * 72
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dpi_w = scale_w * 72.0
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dpi_h = scale_h * 72.0
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return (dpi_w, dpi_h)
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def _find_page_inline_images(page, pageinfo, contentsinfo):
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"Find inline images on the page"
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for n, im in enumerate(contentsinfo.inline_images):
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settings, shorthand = im
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image = {}
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image['name'] = str('inline-%02d' % n)
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image['width'] = settings['/W']
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image['height'] = settings['/H']
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image['bpc'] = settings['/BPC']
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image['color'] = FRIENDLY_COLORSPACE.get(settings['/CS'], '-')
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image['comp'] = FRIENDLY_COMP.get(image['color'], '?')
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if '/F' in settings:
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filter_ = settings['/F']
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if isinstance(filter_, pypdf.generic.ArrayObject):
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filter_ = filter_[0]
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image['enc'] = FRIENDLY_ENCODING.get(filter_, 'image')
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else:
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image['enc'] = 'image'
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dpi_w, dpi_h = _get_dpi(shorthand, (image['width'], image['height']))
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image['dpi_w'], image['dpi_h'] = Decimal(dpi_w), Decimal(dpi_h)
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yield image
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def _find_page_regular_images(page, pageinfo, contentsinfo):
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"Find images stored in XObject resources"
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try:
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page['/Resources']['/XObject']
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except KeyError:
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return
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for xobj in page['/Resources']['/XObject']:
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# PyPDF2 returns the keys as an iterator
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pdfimage = page['/Resources']['/XObject'][xobj]
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if pdfimage['/Subtype'] != '/Image':
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continue
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image = {}
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image['name'] = str(xobj)
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image['width'] = pdfimage['/Width']
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image['height'] = pdfimage['/Height']
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image['bpc'] = pdfimage['/BitsPerComponent']
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if '/Filter' in pdfimage:
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filter_ = pdfimage['/Filter']
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if isinstance(filter_, pypdf.generic.ArrayObject):
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filter_ = filter_[0]
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image['enc'] = FRIENDLY_ENCODING.get(filter_, 'image')
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else:
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image['enc'] = 'image'
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if '/ColorSpace' in pdfimage:
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cs = pdfimage['/ColorSpace']
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if isinstance(cs, pypdf.generic.ArrayObject):
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cs = cs[0]
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image['color'] = FRIENDLY_COLORSPACE.get(cs, '-')
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else:
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image['color'] = 'jpx' if image['enc'] == 'jpx' else '?'
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image['comp'] = FRIENDLY_COMP.get(image['color'], '?')
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image['dpi_w'] = image['dpi_h'] = 0
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for raster in contentsinfo.raster_settings:
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# Loop in case the same image is display multiple times on a page
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if raster[0] != image['name']:
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continue
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shorthand = raster[1]
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dpi_w, dpi_h = _get_dpi(
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shorthand, (image['width'], image['height']))
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# When image is used multiple times take the highest DPI it is
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# rendered at
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image['dpi_w'] = max(dpi_w, image.get('dpi_w', 0))
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image['dpi_h'] = max(dpi_h, image.get('dpi_h', 0))
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image['dpi_w'] = Decimal(image['dpi_w'])
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image['dpi_h'] = Decimal(image['dpi_h'])
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image['dpi'] = (image['dpi_w'] * image['dpi_h']) ** Decimal(0.5)
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yield image
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def _find_page_images(page, pageinfo, contentsinfo):
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yield from _find_page_inline_images(page, pageinfo, contentsinfo)
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yield from _find_page_regular_images(page, pageinfo, contentsinfo)
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def _page_has_text(pdf, page):
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# Simple test
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text = page.extractText()
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if text.strip() != '':
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return True
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# More nuanced test to deal with quirks of Tesseract PDF generation
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# Check if there's a Glyphless font
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try:
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font = page['/Resources']['/Font']
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except KeyError:
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pass
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else:
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font_objects = list(font.keys())
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for font_object in font_objects:
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basefont = font[font_object]['/BaseFont']
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if basefont.endswith('GlyphLessFont'):
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return True
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return False
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def _pdf_get_pageinfo(infile, pageno: int):
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pageinfo = {}
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pageinfo['pageno'] = pageno
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pageinfo['images'] = []
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pdf = pypdf.PdfFileReader(infile)
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page = pdf.pages[pageno]
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pageinfo['has_text'] = _page_has_text(pdf, page)
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width_pt = page.mediaBox.getWidth()
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height_pt = page.mediaBox.getHeight()
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pageinfo['width_inches'] = width_pt / Decimal(72.0)
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pageinfo['height_inches'] = height_pt / Decimal(72.0)
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try:
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contentstream = pypdf.pdf.ContentStream(page.getContents(), pdf)
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except AttributeError as e:
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return pageinfo
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contentsinfo = _interpret_contents(contentstream)
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pageinfo['images'] = [im for im in _find_page_images(
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page, pageinfo, contentsinfo)]
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if pageinfo['images']:
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xres = max(image['dpi_w'] for image in pageinfo['images'])
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yres = max(image['dpi_h'] for image in pageinfo['images'])
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pageinfo['xres'], pageinfo['yres'] = xres, yres
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pageinfo['width_pixels'] = \
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int(round(xres * pageinfo['width_inches']))
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pageinfo['height_pixels'] = \
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int(round(yres * pageinfo['height_inches']))
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return pageinfo
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def pdf_get_all_pageinfo(infile):
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pdf = pypdf.PdfFileReader(infile)
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getcontext().prec = 6
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return [_pdf_get_pageinfo(infile, n) for n in range(pdf.numPages)]
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def main():
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import argparse
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parser = argparse.ArgumentParser()
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parser.add_argument('infile')
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args = parser.parse_args()
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info = pdf_get_all_pageinfo(args.infile)
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from pprint import pprint
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pprint(info)
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if __name__ == '__main__':
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main()
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