184 lines
6.3 KiB
HTML
184 lines
6.3 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<title>Programming with PDFMiner</title>
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<style type="text/css"><!--
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blockquote { background: #eeeeee; }
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.comment { color: darkgreen; }
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--></style>
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</head><body>
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<p>
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<a href="index.html">[Back to PDFMiner homepage]</a>
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<h1>Programming with PDFMiner</h1>
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<p>
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This document explains how to use PDFMiner as a library
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from other applications.
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<ul>
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<li> <a href="#basic">Basic Usage</a>
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<li> <a href="#layout">Layout Analysis</a>
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<li> <a href="#toc">TOC Extraction</a>
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</ul>
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<a name="basic">
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<hr noshade>
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<h2>Basic Usage</h2>
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<p>
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A typical way to parse a PDF file is the following:
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<blockquote><pre>
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from pdfminer.pdfparser import PDFParser, PDFDocument
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from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter
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from pdfminer.pdfdevice import PDFDevice
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<span class="comment"># Open a PDF file.</span>
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fp = open('mypdf.pdf', 'rb')
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<span class="comment"># Create a PDF parser object associated with the file object.</span>
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parser = PDFParser(fp)
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<span class="comment"># Create a PDF document object that stores the document structure.</span>
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doc = PDFDocument()
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<span class="comment"># Connect the parser and document objects.</span>
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parser.set_document(doc)
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doc.set_parser(parser)
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<span class="comment"># Supply the password for initialization.</span>
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<span class="comment"># (If no password is set, give an empty string.)</span>
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doc.initialize(password)
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<span class="comment"># Check if the document allows text extraction. If not, abort.</span>
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if not doc.is_extractable:
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raise PDFTextExtractionNotAllowed
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<span class="comment"># Create a PDF resource manager object that stores shared resources.</span>
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rsrcmgr = PDFResourceManager()
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<span class="comment"># Create a PDF device object.</span>
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device = PDFDevice(rsrcmgr)
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<span class="comment"># Create a PDF interpreter object.</span>
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interpreter = PDFPageInterpreter(rsrcmgr, device)
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<span class="comment"># Process each page contained in the document.</span>
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for page in doc.get_pages():
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interpreter.process_page(page)
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</pre></blockquote>
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<p>
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In PDFMiner, there are several Python classes involved in parsing a PDF file,
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as shown in Figure 1.
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<div align=center>
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<img src="objrel.png"><br>
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<small>Figure 1. Relationships between PDFMiner objects</small>
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</div>
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<a name="layout">
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<hr noshade>
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<h2>Accessing Layout Objects</h2>
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<p>
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PDF documents are more like graphics, rather than text documents.
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It presents no logical structure such as sentences or paragraphs (for most cases).
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PDFMiner attempts to reconstruct some of these structures by performing
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basic layout analysis.
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<p>
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Here is a typical way to do it:
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<blockquote><pre>
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from pdfminer.layout import LAParams
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from pdfminer.converter import PDFPageAggregator
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<span class="comment"># Set parameters for analysis.</span>
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laparams = LAParams()
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<span class="comment"># Create a PDF page aggregator object.</span>
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device = PDFPageAggregator(rsrcmgr, laparams=laparams)
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interpreter = PDFPageInterpreter(rsrcmgr, device)
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for page in doc.get_pages():
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interpreter.process_page(page)
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<span class="comment"># receive the LTPage object for the page.</span>
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layout = device.get_result()
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</pre></blockquote>
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The layout analyzer gives a "<code>LTPage</code>" object for each page
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in the PDF document. The object contains child objects within the page,
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forming a tree-like structure. Figure 2 shows the relationship between
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these objects.
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<div align=center>
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<img src="layout.png"><br>
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<small>Figure 2. Layout objects and its tree structure</small>
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</div>
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<dl>
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<dt> <code>LTPage</code>
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<dd> Represents an entire page. May contain child objects like
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<code>LTTextBox</code>, <code>LTFigure</code>, <code>LTImage</code>, <code>LTRect</code>,
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<code>LTPolygon</code> and <code>LTLine</code>.
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<dt> <code>LTTextBox</code>
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<dd> Represents a group of text chunks that can be contained in a rectangular area.
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Note that this box is created by geometric analysis and does not necessarily
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represents a logical boundary of the text.
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It contains a list of <code>LTTextLine</code> objects.
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<dt> <code>LTTextLine</code>
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<dd> Contains a list of <code>LTChar</code> objects that represent
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a single text line. The characters are aligned either horizontaly
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or vertically, depending on the text's writing mode.
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<dt> <code>LTChar</code>
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<dt> <code>LTText</code>
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<dd> These objects represent an actual letter in the text as a Unicode string.
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Note that, while a <code>LTChar</code> object has actual boundaries,
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<code>LTText</code> objects does not, as these are "virtual" characters,
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inserted by a layout analyzer according to the relationship between two characters
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(e.g. a space).
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<dt> <code>LTFigure</code>
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<dd> Represents an area used by PDF Form objects. PDF Forms can be used to
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present figures or pictures by embedding yet another PDF document within a page.
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Note that <code>LTFigure</code> objects can appear recursively.
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<dt> <code>LTImage</code>
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<dd> Represents an image object. Embedded images can be
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in JPEG or other formats, but currently PDFMiner does not
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pay much attention to graphical objects.
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<dt> <code>LTLine</code>
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<dd> Represents a single straight line shown in a page.
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Could be used for separating texts or figures.
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<dt> <code>LTRect</code>
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<dd> Represents a rectangle shown in a page.
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Could be used for framing another pictures or figures.
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<dt> <code>LTPolygon</code>
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<dd> Represents a polygon in a page.
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</dl>
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<a name="toc">
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<hr noshade>
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<h2>TOC Extraction</h2>
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<p>
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PDFMiner provides functions to access the document's table of contents
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("Outlines").
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<blockquote><pre>
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from pdfminer.pdfparser import PDFParser, PDFDocument
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fp = open('mypdf.pdf', 'rb')
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parser = PDFParser(fp)
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doc = PDFDocument()
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parser.set_document(doc)
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doc.set_parser(parser)
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doc.initialize(password)
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<span class="comment"># Get the outlines of the document.</span>
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outlines = doc.get_outlines()
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for (level,title,dest,a,se) in outlines:
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print (level, title)
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</pre></blockquote>
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<p>
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In some PDF documents, destinations are referred to as page numbers.
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In other PDF documents, destinations are referred to as page numbers plus
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the location within the page. Since PDF does not provide a way to
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point to graphical objects in a page, normally these in-page destinations
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are specified by physical coordinates.
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<hr noshade>
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<address>Yusuke Shinyama</address>
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</body>
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