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    1 /////////////////////////////////////////////////////////////////////
    2 // File:        ocrpara.h
    3 // Description: OCR Paragraph Output Type
    4 // Author:      David Eger
    5 //
    6 // (C) Copyright 2010, Google Inc.
    7 // Licensed under the Apache License, Version 2.0 (the "License");
    8 // you may not use this file except in compliance with the License.
    9 // You may obtain a copy of the License at
   10 // http://www.apache.org/licenses/LICENSE-2.0
   11 // Unless required by applicable law or agreed to in writing, software
   12 // distributed under the License is distributed on an "AS IS" BASIS,
   13 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   14 // See the License for the specific language governing permissions and
   15 // limitations under the License.
   16 //
   17 ///////////////////////////////////////////////////////////////////////
   18 
   19 #ifndef TESSERACT_CCSTRUCT_OCRPARA_H_
   20 #define TESSERACT_CCSTRUCT_OCRPARA_H_
   21 
   22 #include "elst.h"
   23 
   24 #include <tesseract/publictypes.h>
   25 
   26 namespace tesseract {
   27 
   28 class ParagraphModel;
   29 
   30 struct PARA : public ELIST_LINK {
   31 public:
   32   PARA()
   33       : model(nullptr)
   34       , is_list_item(false)
   35       , is_very_first_or_continuation(false)
   36       , has_drop_cap(false) {}
   37 
   38   // We do not own the model, we just reference it.
   39   // model may be nullptr if there is not a good model for this paragraph.
   40   const ParagraphModel *model;
   41 
   42   bool is_list_item;
   43 
   44   // The first paragraph on a page often lacks a first line indent, but should
   45   // still be modeled by the same model as other body text paragraphs on the
   46   // page.
   47   bool is_very_first_or_continuation;
   48 
   49   // Does this paragraph begin with a drop cap?
   50   bool has_drop_cap;
   51 };
   52 
   53 ELISTIZEH(PARA)
   54 
   55 // A geometric model of paragraph indentation and alignment.
   56 //
   57 // Measurements are in pixels. The meaning of the integer arguments changes
   58 // depending upon the value of justification.  Distances less than or equal
   59 // to tolerance apart we take as "equivalent" for the purpose of model
   60 // matching, and in the examples below, we assume tolerance is zero.
   61 //
   62 // justification = LEFT:
   63 //   margin       the "ignored" margin to the left block edge.
   64 //   first_indent indent from the left margin to a typical first text line.
   65 //   body_indent  indent from the left margin of a typical body text line.
   66 //
   67 // justification = RIGHT:
   68 //   margin       the "ignored" margin to the right block edge.
   69 //   first_indent indent from the right margin to a typical first text line.
   70 //   body_indent  indent from the right margin of a typical body text line.
   71 //
   72 // justification = CENTER:
   73 //   margin       ignored
   74 //   first_indent ignored
   75 //   body_indent  ignored
   76 //
   77 //  ====== Extended example, assuming each letter is ten pixels wide: =======
   78 //
   79 // +--------------------------------+
   80 // |      Awesome                   | ParagraphModel(CENTER, 0, 0, 0)
   81 // |   Centered Title               |
   82 // | Paragraph Detection            |
   83 // |      OCR TEAM                  |
   84 // |  10 November 2010              |
   85 // |                                |
   86 // |  Look here, I have a paragraph.| ParagraphModel(LEFT, 0, 20, 0)
   87 // |This paragraph starts at the top|
   88 // |of the page and takes 3 lines.  |
   89 // |  Here I have a second paragraph| ParagraphModel(LEFT, 0, 20, 0)
   90 // |which indicates that the first  |
   91 // |paragraph is not a continuation |
   92 // |from a previous page, as it is  |
   93 // |indented just like this second  |
   94 // |paragraph.                      |
   95 // |   Here is a block quote. It    | ParagraphModel(LEFT, 30, 0, 0)
   96 // |   looks like the prior text    |
   97 // |   but it  is indented  more    |
   98 // |   and is fully justified.      |
   99 // |  So how does one deal with     | ParagraphModel(LEFT, 0, 20, 0)
  100 // |centered text, block quotes,    |
  101 // |normal paragraphs, and lists    |
  102 // |like what follows?              |
  103 // |1. Make a plan.                 | ParagraphModel(LEFT, 0, 0, 30)
  104 // |2. Use a heuristic, for example,| ParagraphModel(LEFT, 0, 0, 30)
  105 // |   looking for lines where the  |
  106 // |   first word of the next line  |
  107 // |   would fit on the previous    |
  108 // |   line.                        |
  109 // |8. Try to implement the plan in | ParagraphModel(LEFT, 0, 0, 30)
  110 // |   Python and try it out.       |
  111 // |4. Determine how to fix the     | ParagraphModel(LEFT, 0, 0, 30)
  112 // |   mistakes.                    |
  113 // |5. Repeat.                      | ParagraphModel(LEFT, 0, 0, 30)
  114 // |  For extra painful penalty work| ParagraphModel(LEFT, 0, 20, 0)
  115 // |you can try to identify source  |
  116 // |code.  Ouch!                    |
  117 // +--------------------------------+
  118 class TESS_API ParagraphModel {
  119 public:
  120   ParagraphModel(tesseract::ParagraphJustification justification, int margin, int first_indent,
  121                  int body_indent, int tolerance)
  122       : justification_(justification)
  123       , margin_(margin)
  124       , first_indent_(first_indent)
  125       , body_indent_(body_indent)
  126       , tolerance_(tolerance) {
  127     // Make one of {first_indent, body_indent} is 0.
  128     int added_margin = first_indent;
  129     if (body_indent < added_margin) {
  130       added_margin = body_indent;
  131     }
  132     margin_ += added_margin;
  133     first_indent_ -= added_margin;
  134     body_indent_ -= added_margin;
  135   }
  136 
  137   ParagraphModel()
  138       : justification_(tesseract::JUSTIFICATION_UNKNOWN)
  139       , margin_(0)
  140       , first_indent_(0)
  141       , body_indent_(0)
  142       , tolerance_(0) {}
  143 
  144   // ValidFirstLine() and ValidBodyLine() take arguments describing a text line
  145   // in a block of text which we are trying to model:
  146   //   lmargin, lindent:  these add up to the distance from the leftmost ink
  147   //                      in the text line to the surrounding text block's left
  148   //                      edge.
  149   //   rmargin, rindent:  these add up to the distance from the rightmost ink
  150   //                      in the text line to the surrounding text block's right
  151   //                      edge.
  152   // The caller determines the division between "margin" and "indent", which
  153   // only actually affect whether we think the line may be centered.
  154   //
  155   // If the amount of whitespace matches the amount of whitespace expected on
  156   // the relevant side of the line (within tolerance_) we say it matches.
  157 
  158   // Return whether a given text line could be a first paragraph line according
  159   // to this paragraph model.
  160   bool ValidFirstLine(int lmargin, int lindent, int rindent, int rmargin) const;
  161 
  162   // Return whether a given text line could be a first paragraph line according
  163   // to this paragraph model.
  164   bool ValidBodyLine(int lmargin, int lindent, int rindent, int rmargin) const;
  165 
  166   tesseract::ParagraphJustification justification() const {
  167     return justification_;
  168   }
  169   int margin() const {
  170     return margin_;
  171   }
  172   int first_indent() const {
  173     return first_indent_;
  174   }
  175   int body_indent() const {
  176     return body_indent_;
  177   }
  178   int tolerance() const {
  179     return tolerance_;
  180   }
  181   bool is_flush() const {
  182     return (justification_ == tesseract::JUSTIFICATION_LEFT ||
  183             justification_ == tesseract::JUSTIFICATION_RIGHT) &&
  184            abs(first_indent_ - body_indent_) <= tolerance_;
  185   }
  186 
  187   // Return whether this model is likely to agree with the other model on most
  188   // paragraphs they are marked.
  189   bool Comparable(const ParagraphModel &other) const;
  190 
  191   std::string ToString() const;
  192 
  193 private:
  194   tesseract::ParagraphJustification justification_;
  195   int margin_;
  196   int first_indent_;
  197   int body_indent_;
  198   int tolerance_;
  199 };
  200 
  201 } // namespace tesseract
  202 
  203 #endif // TESSERACT_CCSTRUCT_OCRPARA_H_