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pdftron::PDF::TextExtractor Class Reference

#include <TextExtractor.h>

Public Types

enum  ProcessingFlags {
  e_no_ligature_exp = 1, e_no_dup_remove = 2, e_punct_break = 4, e_remove_hidden_text = 8,
  e_no_invisible_text = 16, e_no_watermarks = 128
}
 
enum  XMLOutputFlags { e_words_as_elements = 1, e_output_bbox = 2, e_output_style_info = 4 }
 
typedef pdftron::PDF::Style Style
 
typedef pdftron::PDF::Word Word
 
typedef pdftron::PDF::Line Line
 

Public Member Functions

 TextExtractor ()
 
 ~TextExtractor ()
 
void Begin (Page page, const Rect *clip_ptr=0, UInt32 flags=0)
 
void SetOCGContext (OCG::Context *ctx)
 
int GetWordCount ()
 
void SetRightToLeftLanguage (bool rtl)
 
bool GetRightToLeftLanguage ()
 
UString GetAsText (bool dehyphen=true)
 
void GetAsText (UString &out_str, bool dehyphen=true)
 
UString GetTextUnderAnnot (const Annot &annot)
 
void GetTextUnderAnnot (UString &out_str, const Annot &annot)
 
UString GetAsXML (UInt32 xml_output_flags=0)
 
void GetAsXML (UString &out_xml, UInt32 xml_output_flags=0)
 
int GetNumLines ()
 
Line GetFirstLine ()
 
void Destroy ()
 

Detailed Description

TextExtractor is used to analyze a PDF page and extract words and logical structure within a given region. The resulting list of lines and words can be traversed element by element or accessed as a string buffer. The class also includes utility methods to extract PDF text as HTML or XML.

Possible use case scenarios for TextExtractor include:

  • Converting PDF pages to text or XML for content repurposing.
  • Searching PDF pages for specific words or keywords.
  • Indexing large PDF repositories for indexing or content retrieval purposes (i.e. implementing a PDF search engine).
  • Classifying or summarizing PDF documents based on their text content.
  • Finding specific words for content editing purposes (such as splitting pages based on keywords etc).

The main task of TextExtractor is to interpret PDF pages and offer a simple to use API to:

  • Normalize all text content to Unicode.
  • Extract inferred logical structure (word by word, line by line, or paragraph by paragraph).
  • Extract positioning information for every line, word, or a glyph.
  • Extract style information (such as information about the font, font size, font styles, etc) for every line, word, or a glyph.
  • Control the content analysis process. A number of options (such as removal of text obscured by images) is available to let the user direct the flow of content recognition algorithms that will meet their requirements.
  • Offer utility methods to convert PDF page content to text, XML, or HTML.

Note: TextExtractor is analyzing only textual content of the page. This means that the rasterized (e.g. in scanned pages) or vectorized text (where glyphs are converted to path outlines) will not be recognized as text. Please note that it is still possible to extract this content using pdftron.PDF.ElementReader interface.

In some cases TextExtractor may extract text that does not appear to be on the visible page (e.g. when text is obscured by an image or a rectangle). In these situations it is possible to use processing flags such as 'e_remove_hidden_text' and 'e_no_invisible_text' to remove hidden text.

A sample use case (in C++):

... Initialize PDFNet ...
PDFDoc doc(filein);
doc.InitSecurityHandler();
Page page = *doc.PageBegin();
UString text;
txt.GetAsText(text);
// or traverse words one by one...
TextExtractor::Line line = txt.GetFirstLine(), lend;
for (; line!=lend; line=line.GetNextLine()) {
for (word=line.GetFirstWord(); word!=wend; word=word.GetNextWord()) {
text.Assign(word.GetString(), word.GetStringLen());
cout << text << '\n';
}
}

A sample use case (in C#):

... Initialize PDFNet ...
PDFDoc doc = new PDFDoc(filein);
doc.InitSecurityHandler();
Page page = doc.PageBegin().Current();
txt.Begin(page, 0, TextExtractor.ProcessingFlags.e_remove_hidden_text);
string text = txt.GetAsText();
// or traverse words one by one...
TextExtractor.Word word;
for (TextExtractor.Line line = txt.GetFirstLine(); line.IsValid(); line=line.GetNextLine()) {
for (word=line.GetFirstWord(); word.IsValid(); word=word.GetNextWord()) {
Console.WriteLine(word.GetString());
}
}

For full sample code, please take a look at TextExtract sample project.

Definition at line 106 of file TextExtractor.h.

Member Typedef Documentation

Member Enumeration Documentation

Processing options that can be passed in Begin() method to direct the flow of content recognition algorithms

Enumerator
e_no_ligature_exp 
e_no_dup_remove 
e_punct_break 
e_remove_hidden_text 
e_no_invisible_text 
e_no_watermarks 

Definition at line 123 of file TextExtractor.h.

Flags controlling the structure of XML output in a call to GetAsXML().

Enumerator
e_words_as_elements 
e_output_bbox 
e_output_style_info 

Definition at line 227 of file TextExtractor.h.

Constructor & Destructor Documentation

pdftron::PDF::TextExtractor::TextExtractor ( )

Constructor and destructor

pdftron::PDF::TextExtractor::~TextExtractor ( )

Member Function Documentation

void pdftron::PDF::TextExtractor::Begin ( Page  page,
const Rect clip_ptr = 0,
UInt32  flags = 0 
)

Start reading the page.

Parameters
pagePage to read.
clip_ptrA pointer to the optional clipping rectangle. This parameter can be used to selectively read text from a given rectangle.
flagsA list of ProcessingFlags used to control text extraction algorithm.
void pdftron::PDF::TextExtractor::Destroy ( )

Frees the native memory of the object.

UString pdftron::PDF::TextExtractor::GetAsText ( bool  dehyphen = true)

Get all words in the current selection as a single string.

Parameters
out_strThe string containing all words in the current selection. Words will be separated with space (i.e. ' ') or new line (i.e. '
') characters.
dehyphenIf true, finds and removes hyphens that split words across two lines. Hyphens are often used a the end of lines as an indicator that a word spans two lines. Hyphen detection enables removal of hyphen character and merging of text runs to form a single word. This option has no effect on Tagged PDF files.
void pdftron::PDF::TextExtractor::GetAsText ( UString out_str,
bool  dehyphen = true 
)
UString pdftron::PDF::TextExtractor::GetAsXML ( UInt32  xml_output_flags = 0)

Get text content in a form of an XML string.

Parameters
out_xml- The string containing XML output.
xml_output_flags- flags controlling XML output. For more information, please see TextExtract::XMLOutputFlags.

XML output will be encoded in UTF-8 and will have the following structure:

<Page num="1 crop_box="0, 0, 612, 792" media_box="0, 0, 612, 792" rotate="0">
<Flow id="1">
<Para id="1">
<Line box="72, 708.075, 467.895, 10.02" style="font-family:Calibri; font-size:10.02; color: #000000;">
<Word box="72, 708.075, 30.7614, 10.02">PDFNet</Word>
<Word box="106.188, 708.075, 15.9318, 10.02">SDK</Word>
<Word box="125.617, 708.075, 6.22242, 10.02">is</Word>
...
</Line>
</Para>
</Flow>
</Page>

The above XML output was generated by passing the following union of flags in the call to GetAsXML(): (TextExtractor::e_words_as_elements | TextExtractor::e_output_bbox | TextExtractor::e_output_style_info)

In case 'xml_output_flags' was not specified, the default XML output would look as follows:

<Page num="1 crop_box="0, 0, 612, 792" media_box="0, 0, 612, 792" rotate="0"> <Flow id="1"> <Para id="1"> <Line>PDFNet SDK is an amazingly comprehensive, high-quality PDF developer toolkit...</Line> <Line>levels. Using the PDFNet PDF library, ...</Line> ...

</Flow> </Page>

void pdftron::PDF::TextExtractor::GetAsXML ( UString out_xml,
UInt32  xml_output_flags = 0 
)
Line pdftron::PDF::TextExtractor::GetFirstLine ( )
Returns
The first line of text on the selected page.
Note
To traverse the list of all text lines on the page use line.GetNextLine().
To traverse the list of all word on a given line use line.GetFirstWord().
int pdftron::PDF::TextExtractor::GetNumLines ( )
Returns
The number of lines of text on the selected page.
bool pdftron::PDF::TextExtractor::GetRightToLeftLanguage ( )
Returns
the directionality of text extractor.
UString pdftron::PDF::TextExtractor::GetTextUnderAnnot ( const Annot annot)

Get all the characters that intersect an annotation.

Parameters
annotThe annotation to intersect with.
void pdftron::PDF::TextExtractor::GetTextUnderAnnot ( UString out_str,
const Annot annot 
)
int pdftron::PDF::TextExtractor::GetWordCount ( )
Returns
the number of words on the page.
void pdftron::PDF::TextExtractor::SetOCGContext ( OCG::Context ctx)

Sets the Optional Content Group (OCG) context that should be used when processing the document. This function can be used to change the current OCG context. Optional content (such as PDF layers) will be selectively processed based on the states of optional content groups in the given context.

Parameters
ctxOptional Content Group (OCG) context, or NULL if TextExtractor should process all content on the page.
void pdftron::PDF::TextExtractor::SetRightToLeftLanguage ( bool  rtl)

Sets the directionality of text extractor. Must be called before the processing of a page started.

Parameters
rtlmode reverses the directionality of TextExtractor algorithm.

The documentation for this class was generated from the following file: