tesseract/src/textord/linefind.h

///////////////////////////////////////////////////////////////////////
// File:        linefind.h
// Description: Class to find vertical lines in an image and create
//              a corresponding list of empty blobs.
// Author:      Ray Smith
// Created:     Thu Mar 20 09:49:01 PDT 2008
//
// (C) Copyright 2008, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
///////////////////////////////////////////////////////////////////////

#ifndef TESSERACT_TEXTORD_LINEFIND_H_
#define TESSERACT_TEXTORD_LINEFIND_H_

struct Boxa;
struct Pix;
struct Pixa;
class C_BLOB_LIST;
class BLOBNBOX_LIST;
class ICOORD;

namespace tesseract {

class TabVector_LIST;

/**
 * The LineFinder class is a simple static function wrapper class that mainly
 * exposes the FindVerticalLines function.
 */
class LineFinder {
 public:
  /**
   * Finds vertical and horizontal line objects in the given pix and removes
   * them.
   *
   * Uses the given resolution to determine size thresholds instead of any
   * that may be present in the pix.
   *
   * The output vertical_x and vertical_y contain a sum of the output vectors,
   * thereby giving the mean vertical direction.
   *
   * If pix_music_mask != nullptr, and music is detected, a mask of the staves
   * and anything that is connected (bars, notes etc.) will be returned in
   * pix_music_mask, the mask subtracted from pix, and the lines will not
   * appear in v_lines or h_lines.
   *
   * The output vectors are owned by the list and Frozen (cannot refit) by
   * having no boxes, as there is no need to refit or merge separator lines.
   *
   * The detected lines are removed from the pix.
   */
  static void FindAndRemoveLines(int resolution,  bool debug, Pix* pix,
                                 int* vertical_x, int* vertical_y,
                                 Pix** pix_music_mask,
                                 TabVector_LIST* v_lines,
                                 TabVector_LIST* h_lines);

  /**
   * Converts the Boxa array to a list of C_BLOB, getting rid of severely
   * overlapping outlines and those that are children of a bigger one.
   *
   * The output is a list of C_BLOBs that are owned by the list.
   *
   * The C_OUTLINEs in the C_BLOBs contain no outline data - just empty
   * bounding boxes. The Boxa is consumed and destroyed.
   */
  static void ConvertBoxaToBlobs(int image_width, int image_height,
                                 Boxa** boxes, C_BLOB_LIST* blobs);

 private:
  // Finds vertical line objects in pix_vline and removes them from src_pix.
  // Uses the given resolution to determine size thresholds instead of any
  // that may be present in the pix.
  // The output vertical_x and vertical_y contain a sum of the output vectors,
  // thereby giving the mean vertical direction.
  // The output vectors are owned by the list and Frozen (cannot refit) by
  // having no boxes, as there is no need to refit or merge separator lines.
  // If no good lines are found, pix_vline is destroyed.
  static void FindAndRemoveVLines(int resolution,
                                  Pix* pix_intersections,
                                  int* vertical_x, int* vertical_y,
                                  Pix** pix_vline, Pix* pix_non_vline,
                                  Pix* src_pix, TabVector_LIST* vectors);


  // Finds horizontal line objects in pix_vline and removes them from src_pix.
  // Uses the given resolution to determine size thresholds instead of any
  // that may be present in the pix.
  // The output vertical_x and vertical_y contain a sum of the output vectors,
  // thereby giving the mean vertical direction.
  // The output vectors are owned by the list and Frozen (cannot refit) by
  // having no boxes, as there is no need to refit or merge separator lines.
  // If no good lines are found, pix_hline is destroyed.
  static void FindAndRemoveHLines(int resolution,
                                  Pix* pix_intersections,
                                  int vertical_x, int vertical_y,
                                  Pix** pix_hline, Pix* pix_non_hline,
                                  Pix* src_pix, TabVector_LIST* vectors);

  // Finds vertical lines in the given list of BLOBNBOXes. bleft and tright
  // are the bounds of the image on which the input line_bblobs were found.
  // The input line_bblobs list is const really.
  // The output vertical_x and vertical_y are the total of all the vectors.
  // The output list of TabVector makes no reference to the input BLOBNBOXes.
  static void FindLineVectors(const ICOORD& bleft, const ICOORD& tright,
                              BLOBNBOX_LIST* line_bblobs,
                              int* vertical_x, int* vertical_y,
                              TabVector_LIST* vectors);

  // Most of the heavy lifting of line finding. Given src_pix and its separate
  // resolution, returns image masks:
  // Returns image masks:
  // pix_vline           candidate vertical lines.
  // pix_non_vline       pixels that didn't look like vertical lines.
  // pix_hline           candidate horizontal lines.
  // pix_non_hline       pixels that didn't look like horizontal lines.
  // pix_intersections   pixels where vertical and horizontal lines meet.
  // pix_music_mask      candidate music staves.
  // This function promises to initialize all the output (2nd level) pointers,
  // but any of the returns that are empty will be nullptr on output.
  // None of the input (1st level) pointers may be nullptr except pix_music_mask,
  // which will disable music detection, and pixa_display, which is for debug.
  static void GetLineMasks(int resolution, Pix* src_pix,
                           Pix** pix_vline, Pix** pix_non_vline,
                           Pix** pix_hline, Pix** pix_non_hline,
                           Pix** pix_intersections, Pix** pix_music_mask,
                           Pixa* pixa_display);

  // Returns a list of boxes corresponding to the candidate line segments. Sets
  // the line_crossings member of the boxes so we can later determine the number
  // of intersections touched by a full line.
  static void GetLineBoxes(bool horizontal_lines,
                           Pix* pix_lines, Pix* pix_intersections,
                           C_BLOB_LIST* line_cblobs,
                           BLOBNBOX_LIST* line_bblobs);
};

}  // namespace tesseract.

#endif  // TESSERACT_TEXTORD_LINEFIND_H_