pageinfo: handle stencil masks when stack depth > 0
This commit is contained in:
James R. Barlow
+53
-24
@@ -72,11 +72,38 @@ def _shorthand_from_matrix(matrix):
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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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RasterSettings = namedtuple('RasterSettings',
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['name', 'shorthand', 'stack_depth'])
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InlineSettings = namedtuple('InlineSettings',
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['settings', 'shorthand', 'stack_depth'])
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ContentsInfo = namedtuple('ContentsInfo', ['raster_settings', 'inline_images'])
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def _interpret_contents(contentstream):
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"""Interpret the PDF content stream
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The stack represents the state of the PDF graphics stack. We are only
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interested in the current transformation matrix (CTM) so we only track
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this object; a full implementation would need to track many other items.
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The CTM is initialized to the mapping from user space to device space.
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PDF units are 1/72". In a PDF viewer or printer this matrix is initialized
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to the transformation to device space. For example if set to
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(1/72, 0, 0, 1/72, 0, 0) then all units would be calculated in inches.
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Images are always considered to be (0, 0) -> (1, 1). Before drawing an
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image there should be a 'cm' that sets up an image coordinate system
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where drawing from (0, 0) -> (1, 1) will draw on the desired area of the
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page.
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PDF units suit our needs so we initialize ctm to the identity matrix.
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PyPDF2 replaces inline images with a fake "INLINE IMAGE" operator.
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"""
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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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@@ -96,12 +123,15 @@ def _interpret_contents(contentstream):
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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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raster = RasterSettings(
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name=image_name, shorthand=_shorthand_from_matrix(ctm),
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stack_depth=len(stack))
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image_raster_settings.append(raster)
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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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inline = InlineSettings(
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settings=settings, shorthand=_shorthand_from_matrix(ctm),
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stack_depth=len(stack))
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return ContentsInfo(
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raster_settings=image_raster_settings,
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@@ -175,24 +205,24 @@ def _get_dpi(ctm_shorthand, image_size):
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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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for n, inline in enumerate(contentsinfo.inline_images):
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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['width'] = inline.settings['/W']
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image['height'] = inline.settings['/H']
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image['bpc'] = inline.settings['/BPC']
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image['color'] = FRIENDLY_COLORSPACE.get(inline.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 '/F' in inline.settings:
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filter_ = inline.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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dpi_w, dpi_h = _get_dpi(
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inline.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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@@ -253,19 +283,18 @@ def _find_page_regular_images(page, pageinfo, contentsinfo):
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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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if raster.name != image['name']:
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continue
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shorthand = raster[1]
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if image['type'] == 'stencil':
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# Stencil masks are implicitly scaled over the whole page
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# Images that are used in explicit masks are not drawn directly
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# but drawn by the image they mask over, so they will never
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# be called for in raster settings
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if shorthand != (1, 0, 0, 1, 0, 0):
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raise NotImplementedError(
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"Don't know how to handle "
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"stencil masks when graphics stack depth > 0.")
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shorthand = raster.shorthand
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if image['type'] == 'stencil' and raster.stack_depth == 0:
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# By observation, it seems that stencil masks are implicitly
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# scaled over the whole page if they are ever drawn when the
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# graphics stack depth is 0. I can't find this documented
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# in the reference manual but it is consistent with how
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# Acrobat and OS X Preview behave. I also can't find a
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# description, generally, of what should happen when an image
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# is drawn with the default CTM.
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page_w = float(pageinfo['width_inches']) * 72.0
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page_h = float(pageinfo['height_inches']) * 72.0
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shorthand = (page_w, 0.0, 0.0,
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