--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/tesseract/src/textord/linefind.cpp	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,744 @@
+///////////////////////////////////////////////////////////////////////
+// File:        linefind.cpp
+// Description: Class to find vertical lines in an image and create
+//              a corresponding list of empty blobs.
+// Author:      Ray Smith
+//
+// (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.
+//
+///////////////////////////////////////////////////////////////////////
+
+#ifdef HAVE_CONFIG_H
+#  include "config_auto.h"
+#endif
+
+#include "alignedblob.h"
+#include "blobbox.h"
+#include "crakedge.h" // for CRACKEDGE
+#include "edgblob.h"
+#include "linefind.h"
+#include "tabvector.h"
+
+#include <algorithm>
+
+namespace tesseract {
+
+/// Denominator of resolution makes max pixel width to allow thin lines.
+const int kThinLineFraction = 20;
+/// Denominator of resolution makes min pixels to demand line lengths to be.
+const int kMinLineLengthFraction = 4;
+/// Spacing of cracks across the page to break up tall vertical lines.
+const int kCrackSpacing = 100;
+/// Grid size used by line finder. Not very critical.
+const int kLineFindGridSize = 50;
+// Min width of a line in pixels to be considered thick.
+const int kMinThickLineWidth = 12;
+// Max size of line residue. (The pixels that fail the long thin opening, and
+// therefore don't make it to the candidate line mask, but are nevertheless
+// part of the line.)
+const int kMaxLineResidue = 6;
+// Min length in inches of a line segment that exceeds kMinThickLineWidth in
+// thickness. (Such lines shouldn't break by simple image degradation.)
+const double kThickLengthMultiple = 0.75;
+// Max fraction of line box area that can be occupied by non-line pixels.
+const double kMaxNonLineDensity = 0.25;
+// Max height of a music stave in inches.
+const double kMaxStaveHeight = 1.0;
+// Minimum fraction of pixels in a music rectangle connected to the staves.
+const double kMinMusicPixelFraction = 0.75;
+
+// Erases the unused blobs from the line_pix image, taking into account
+// whether this was a horizontal or vertical line set.
+static void RemoveUnusedLineSegments(bool horizontal_lines, BLOBNBOX_LIST *line_bblobs,
+                                     Image line_pix) {
+  int height = pixGetHeight(line_pix);
+  BLOBNBOX_IT bbox_it(line_bblobs);
+  for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
+    BLOBNBOX *blob = bbox_it.data();
+    if (blob->left_tab_type() != TT_VLINE) {
+      const TBOX &box = blob->bounding_box();
+      Box *pixbox = nullptr;
+      if (horizontal_lines) {
+        // Horizontal lines are in tess format and also have x and y flipped
+        // (to use FindVerticalAlignment) so we have to flip x and y and then
+        // convert to Leptonica by height - flipped x (ie the right edge).
+        // See GetLineBoxes for more explanation.
+        pixbox = boxCreate(box.bottom(), height - box.right(), box.height(), box.width());
+      } else {
+        // For vertical lines, just flip upside-down to convert to Leptonica.
+        // The y position of the box in Leptonica terms is the distance from
+        // the top of the image to the top of the box.
+        pixbox = boxCreate(box.left(), height - box.top(), box.width(), box.height());
+      }
+      pixClearInRect(line_pix, pixbox);
+      boxDestroy(&pixbox);
+    }
+  }
+}
+
+// Helper subtracts the line_pix image from the src_pix, and removes residue
+// as well by removing components that touch the line, but are not in the
+// non_line_pix mask. It is assumed that the non_line_pix mask has already
+// been prepared to required accuracy.
+static void SubtractLinesAndResidue(Image line_pix, Image non_line_pix,
+                                    Image src_pix) {
+  // First remove the lines themselves.
+  pixSubtract(src_pix, src_pix, line_pix);
+  // Subtract the non-lines from the image to get the residue.
+  Image residue_pix = pixSubtract(nullptr, src_pix, non_line_pix);
+  // Dilate the lines so they touch the residue.
+  Image fat_line_pix = pixDilateBrick(nullptr, line_pix, 3, 3);
+  // Seed fill the fat lines to get all the residue.
+  pixSeedfillBinary(fat_line_pix, fat_line_pix, residue_pix, 8);
+  // Subtract the residue from the original image.
+  pixSubtract(src_pix, src_pix, fat_line_pix);
+  fat_line_pix.destroy();
+  residue_pix.destroy();
+}
+
+// Returns the maximum strokewidth in the given binary image by doubling
+// the maximum of the distance function.
+static int MaxStrokeWidth(Image pix) {
+  Image dist_pix = pixDistanceFunction(pix, 4, 8, L_BOUNDARY_BG);
+  int width = pixGetWidth(dist_pix);
+  int height = pixGetHeight(dist_pix);
+  int wpl = pixGetWpl(dist_pix);
+  l_uint32 *data = pixGetData(dist_pix);
+  // Find the maximum value in the distance image.
+  int max_dist = 0;
+  for (int y = 0; y < height; ++y) {
+    for (int x = 0; x < width; ++x) {
+      int pixel = GET_DATA_BYTE(data, x);
+      if (pixel > max_dist) {
+        max_dist = pixel;
+      }
+    }
+    data += wpl;
+  }
+  dist_pix.destroy();
+  return max_dist * 2;
+}
+
+// Returns the number of components in the intersection_pix touched by line_box.
+static int NumTouchingIntersections(Box *line_box, Image intersection_pix) {
+  if (intersection_pix == nullptr) {
+    return 0;
+  }
+  Image rect_pix = pixClipRectangle(intersection_pix, line_box, nullptr);
+  Boxa *boxa = pixConnComp(rect_pix, nullptr, 8);
+  rect_pix.destroy();
+  if (boxa == nullptr) {
+    return false;
+  }
+  int result = boxaGetCount(boxa);
+  boxaDestroy(&boxa);
+  return result;
+}
+
+// Returns the number of black pixels found in the box made by adding the line
+// width to both sides of the line bounding box. (Increasing the smallest
+// dimension of the bounding box.)
+static int CountPixelsAdjacentToLine(int line_width, Box *line_box, Image nonline_pix) {
+  l_int32 x, y, box_width, box_height;
+  boxGetGeometry(line_box, &x, &y, &box_width, &box_height);
+  if (box_width > box_height) {
+    // horizontal line.
+    int bottom = std::min(pixGetHeight(nonline_pix), y + box_height + line_width);
+    y = std::max(0, y - line_width);
+    box_height = bottom - y;
+  } else {
+    // Vertical line.
+    int right = std::min(pixGetWidth(nonline_pix), x + box_width + line_width);
+    x = std::max(0, x - line_width);
+    box_width = right - x;
+  }
+  Box *box = boxCreate(x, y, box_width, box_height);
+  Image rect_pix = pixClipRectangle(nonline_pix, box, nullptr);
+  boxDestroy(&box);
+  l_int32 result;
+  pixCountPixels(rect_pix, &result, nullptr);
+  rect_pix.destroy();
+  return result;
+}
+
+// Helper erases false-positive line segments from the input/output line_pix.
+// 1. Since thick lines shouldn't really break up, we can eliminate some false
+//    positives by marking segments that are at least kMinThickLineWidth
+//    thickness, yet have a length less than min_thick_length.
+// 2. Lines that don't have at least 2 intersections with other lines and have
+//    a lot of neighbouring non-lines are probably not lines (perhaps arabic
+//    or Hindi words, or underlines.)
+// Bad line components are erased from line_pix.
+// Returns the number of remaining connected components.
+static int FilterFalsePositives(int resolution, Image nonline_pix, Image intersection_pix,
+                                Image line_pix) {
+  int min_thick_length = static_cast<int>(resolution * kThickLengthMultiple);
+  Pixa *pixa = nullptr;
+  Boxa *boxa = pixConnComp(line_pix, &pixa, 8);
+  // Iterate over the boxes to remove false positives.
+  int nboxes = boxaGetCount(boxa);
+  int remaining_boxes = nboxes;
+  for (int i = 0; i < nboxes; ++i) {
+    Box *box = boxaGetBox(boxa, i, L_CLONE);
+    l_int32 x, y, box_width, box_height;
+    boxGetGeometry(box, &x, &y, &box_width, &box_height);
+    Image comp_pix = pixaGetPix(pixa, i, L_CLONE);
+    int max_width = MaxStrokeWidth(comp_pix);
+    comp_pix.destroy();
+    bool bad_line = false;
+    // If the length is too short to stand-alone as a line, and the box width
+    // is thick enough, and the stroke width is thick enough it is bad.
+    if (box_width >= kMinThickLineWidth && box_height >= kMinThickLineWidth &&
+        box_width < min_thick_length && box_height < min_thick_length &&
+        max_width > kMinThickLineWidth) {
+      // Too thick for the length.
+      bad_line = true;
+    }
+    if (!bad_line && (NumTouchingIntersections(box, intersection_pix) < 2)) {
+      // Test non-line density near the line.
+      int nonline_count = CountPixelsAdjacentToLine(max_width, box, nonline_pix);
+      if (nonline_count > box_height * box_width * kMaxNonLineDensity) {
+        bad_line = true;
+      }
+    }
+    if (bad_line) {
+      // Not a good line.
+      pixClearInRect(line_pix, box);
+      --remaining_boxes;
+    }
+    boxDestroy(&box);
+  }
+  pixaDestroy(&pixa);
+  boxaDestroy(&boxa);
+  return remaining_boxes;
+}
+
+// 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) {
+  C_OUTLINE_LIST outlines;
+  C_OUTLINE_IT ol_it = &outlines;
+  // Iterate the boxes to convert to outlines.
+  int nboxes = boxaGetCount(*boxes);
+  for (int i = 0; i < nboxes; ++i) {
+    l_int32 x, y, width, height;
+    boxaGetBoxGeometry(*boxes, i, &x, &y, &width, &height);
+    // Make a C_OUTLINE from the leptonica box. This is a bit of a hack,
+    // as there is no outline, just a bounding box, but with some very
+    // small changes to coutln.cpp, it works nicely.
+    ICOORD top_left(x, y);
+    ICOORD bot_right(x + width, y + height);
+    CRACKEDGE startpt;
+    startpt.pos = top_left;
+    auto *outline = new C_OUTLINE(&startpt, top_left, bot_right, 0);
+    ol_it.add_after_then_move(outline);
+  }
+  // Use outlines_to_blobs to convert the outlines to blobs and find
+  // overlapping and contained objects. The output list of blobs in the block
+  // has all the bad ones filtered out and deleted.
+  BLOCK block;
+  ICOORD page_tl(0, 0);
+  ICOORD page_br(image_width, image_height);
+  outlines_to_blobs(&block, page_tl, page_br, &outlines);
+  // Transfer the created blobs to the output list.
+  C_BLOB_IT blob_it(blobs);
+  blob_it.add_list_after(block.blob_list());
+  // The boxes aren't needed any more.
+  boxaDestroy(boxes);
+}
+
+// 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, Image pix_lines, Image pix_intersections,
+                         C_BLOB_LIST *line_cblobs, BLOBNBOX_LIST *line_bblobs) {
+  // Put a single pixel crack in every line at an arbitrary spacing,
+  // so they break up and the bounding boxes can be used to get the
+  // direction accurately enough without needing outlines.
+  int wpl = pixGetWpl(pix_lines);
+  int width = pixGetWidth(pix_lines);
+  int height = pixGetHeight(pix_lines);
+  l_uint32 *data = pixGetData(pix_lines);
+  if (horizontal_lines) {
+    for (int y = 0; y < height; ++y, data += wpl) {
+      for (int x = kCrackSpacing; x < width; x += kCrackSpacing) {
+        CLEAR_DATA_BIT(data, x);
+      }
+    }
+  } else {
+    for (int y = kCrackSpacing; y < height; y += kCrackSpacing) {
+      memset(data + wpl * y, 0, wpl * sizeof(*data));
+    }
+  }
+  // Get the individual connected components
+  Boxa *boxa = pixConnComp(pix_lines, nullptr, 8);
+  ConvertBoxaToBlobs(width, height, &boxa, line_cblobs);
+  // Make the BLOBNBOXes from the C_BLOBs.
+  C_BLOB_IT blob_it(line_cblobs);
+  BLOBNBOX_IT bbox_it(line_bblobs);
+  for (blob_it.mark_cycle_pt(); !blob_it.cycled_list(); blob_it.forward()) {
+    C_BLOB *cblob = blob_it.data();
+    auto *bblob = new BLOBNBOX(cblob);
+    bbox_it.add_to_end(bblob);
+    // Determine whether the line segment touches two intersections.
+    const TBOX &bbox = bblob->bounding_box();
+    Box *box = boxCreate(bbox.left(), bbox.bottom(), bbox.width(), bbox.height());
+    bblob->set_line_crossings(NumTouchingIntersections(box, pix_intersections));
+    boxDestroy(&box);
+    // Transform the bounding box prior to finding lines. To save writing
+    // two line finders, flip x and y for horizontal lines and re-use the
+    // tab-stop detection code. For vertical lines we still have to flip the
+    // y-coordinates to switch from leptonica coords to tesseract coords.
+    if (horizontal_lines) {
+      // Note that we have Leptonica coords stored in a Tesseract box, so that
+      // bbox.bottom(), being the MIN y coord, is actually the top, so to get
+      // back to Leptonica coords in RemoveUnusedLineSegments, we have to
+      // use height - box.right() as the top, which looks very odd.
+      TBOX new_box(height - bbox.top(), bbox.left(), height - bbox.bottom(), bbox.right());
+      bblob->set_bounding_box(new_box);
+    } else {
+      TBOX new_box(bbox.left(), height - bbox.top(), bbox.right(), height - bbox.bottom());
+      bblob->set_bounding_box(new_box);
+    }
+  }
+}
+
+// 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) {
+  BLOBNBOX_IT bbox_it(line_bblobs);
+  int b_count = 0;
+  // Put all the blobs into the grid to find the lines, and move the blobs
+  // to the output lists.
+  AlignedBlob blob_grid(kLineFindGridSize, bleft, tright);
+  for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
+    BLOBNBOX *bblob = bbox_it.data();
+    bblob->set_left_tab_type(TT_MAYBE_ALIGNED);
+    bblob->set_left_rule(bleft.x());
+    bblob->set_right_rule(tright.x());
+    bblob->set_left_crossing_rule(bleft.x());
+    bblob->set_right_crossing_rule(tright.x());
+    blob_grid.InsertBBox(false, true, bblob);
+    ++b_count;
+  }
+  if (b_count == 0) {
+    return;
+  }
+
+  // Search the entire grid, looking for vertical line vectors.
+  BlobGridSearch lsearch(&blob_grid);
+  BLOBNBOX *bbox;
+  TabVector_IT vector_it(vectors);
+  *vertical_x = 0;
+  *vertical_y = 1;
+  lsearch.StartFullSearch();
+  while ((bbox = lsearch.NextFullSearch()) != nullptr) {
+    if (bbox->left_tab_type() == TT_MAYBE_ALIGNED) {
+      const TBOX &box = bbox->bounding_box();
+      if (AlignedBlob::WithinTestRegion(2, box.left(), box.bottom())) {
+        tprintf("Finding line vector starting at bbox (%d,%d)\n", box.left(), box.bottom());
+      }
+      AlignedBlobParams align_params(*vertical_x, *vertical_y, box.width());
+      TabVector *vector =
+          blob_grid.FindVerticalAlignment(align_params, bbox, vertical_x, vertical_y);
+      if (vector != nullptr) {
+        vector->Freeze();
+        vector_it.add_to_end(vector);
+      }
+    }
+  }
+}
+
+// Returns a Pix music mask if music is detected.
+// Any vertical line that has at least 5 intersections in sufficient density
+// is taken to be a bar. Bars are used as a seed and the entire touching
+// component is added to the output music mask and subtracted from the lines.
+// Returns nullptr and does minimal work if no music is found.
+static Image FilterMusic(int resolution, Image pix_closed, Image pix_vline, Image pix_hline,
+                        bool &v_empty, bool &h_empty) {
+  int max_stave_height = static_cast<int>(resolution * kMaxStaveHeight);
+  Image intersection_pix = pix_vline & pix_hline;
+  Boxa *boxa = pixConnComp(pix_vline, nullptr, 8);
+  // Iterate over the boxes to find music bars.
+  int nboxes = boxaGetCount(boxa);
+  Image music_mask = nullptr;
+  for (int i = 0; i < nboxes; ++i) {
+    Box *box = boxaGetBox(boxa, i, L_CLONE);
+    l_int32 x, y, box_width, box_height;
+    boxGetGeometry(box, &x, &y, &box_width, &box_height);
+    int joins = NumTouchingIntersections(box, intersection_pix);
+    // Test for the join density being at least 5 per max_stave_height,
+    // ie (joins-1)/box_height >= (5-1)/max_stave_height.
+    if (joins >= 5 && (joins - 1) * max_stave_height >= 4 * box_height) {
+      // This is a music bar. Add to the mask.
+      if (music_mask == nullptr) {
+        music_mask = pixCreate(pixGetWidth(pix_vline), pixGetHeight(pix_vline), 1);
+      }
+      pixSetInRect(music_mask, box);
+    }
+    boxDestroy(&box);
+  }
+  boxaDestroy(&boxa);
+  intersection_pix.destroy();
+  if (music_mask != nullptr) {
+    // The mask currently contains just the bars. Use the mask as a seed
+    // and the pix_closed as the mask for a seedfill to get all the
+    // intersecting staves.
+    pixSeedfillBinary(music_mask, music_mask, pix_closed, 8);
+    // Filter out false positives. CCs in the music_mask should be the vast
+    // majority of the pixels in their bounding boxes, as we expect just a
+    // tiny amount of text, a few phrase marks, and crescendo etc left.
+    Boxa *boxa = pixConnComp(music_mask, nullptr, 8);
+    // Iterate over the boxes to find music components.
+    int nboxes = boxaGetCount(boxa);
+    for (int i = 0; i < nboxes; ++i) {
+      Box *box = boxaGetBox(boxa, i, L_CLONE);
+      Image rect_pix = pixClipRectangle(music_mask, box, nullptr);
+      l_int32 music_pixels;
+      pixCountPixels(rect_pix, &music_pixels, nullptr);
+      rect_pix.destroy();
+      rect_pix = pixClipRectangle(pix_closed, box, nullptr);
+      l_int32 all_pixels;
+      pixCountPixels(rect_pix, &all_pixels, nullptr);
+      rect_pix.destroy();
+      if (music_pixels < kMinMusicPixelFraction * all_pixels) {
+        // False positive. Delete from the music mask.
+        pixClearInRect(music_mask, box);
+      }
+      boxDestroy(&box);
+    }
+    boxaDestroy(&boxa);
+    if (music_mask.isZero()) {
+      music_mask.destroy();
+    } else {
+      pixSubtract(pix_vline, pix_vline, music_mask);
+      pixSubtract(pix_hline, pix_hline, music_mask);
+      // We may have deleted all the lines
+      v_empty = pix_vline.isZero();
+      h_empty = pix_hline.isZero();
+    }
+  }
+  return music_mask;
+}
+
+// Most of the heavy lifting of line finding. Given src_pix and its separate
+// resolution, 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, Image src_pix, Image *pix_vline, Image *pix_non_vline,
+                         Image *pix_hline, Image *pix_non_hline, Image *pix_intersections,
+                         Image *pix_music_mask, Pixa *pixa_display) {
+  Image pix_closed = nullptr;
+  Image pix_hollow = nullptr;
+
+  int max_line_width = resolution / kThinLineFraction;
+  int min_line_length = resolution / kMinLineLengthFraction;
+  if (pixa_display != nullptr) {
+    tprintf("Image resolution = %d, max line width = %d, min length=%d\n", resolution,
+            max_line_width, min_line_length);
+  }
+  int closing_brick = max_line_width / 3;
+
+  // Close up small holes, making it less likely that false alarms are found
+  // in thickened text (as it will become more solid) and also smoothing over
+  // some line breaks and nicks in the edges of the lines.
+  pix_closed = pixCloseBrick(nullptr, src_pix, closing_brick, closing_brick);
+  if (pixa_display != nullptr) {
+    pixaAddPix(pixa_display, pix_closed, L_CLONE);
+  }
+  // Open up with a big box to detect solid areas, which can then be
+  // subtracted. This is very generous and will leave in even quite wide
+  // lines.
+  Image pix_solid = pixOpenBrick(nullptr, pix_closed, max_line_width, max_line_width);
+  if (pixa_display != nullptr) {
+    pixaAddPix(pixa_display, pix_solid, L_CLONE);
+  }
+  pix_hollow = pixSubtract(nullptr, pix_closed, pix_solid);
+
+  pix_solid.destroy();
+
+  // Now open up in both directions independently to find lines of at least
+  // 1 inch/kMinLineLengthFraction in length.
+  if (pixa_display != nullptr) {
+    pixaAddPix(pixa_display, pix_hollow, L_CLONE);
+  }
+  *pix_vline = pixOpenBrick(nullptr, pix_hollow, 1, min_line_length);
+  *pix_hline = pixOpenBrick(nullptr, pix_hollow, min_line_length, 1);
+
+  pix_hollow.destroy();
+
+  // Lines are sufficiently rare, that it is worth checking for a zero image.
+  bool v_empty = pix_vline->isZero();
+  bool h_empty = pix_hline->isZero();
+  if (pix_music_mask != nullptr) {
+    if (!v_empty && !h_empty) {
+      *pix_music_mask =
+          FilterMusic(resolution, pix_closed, *pix_vline, *pix_hline, v_empty, h_empty);
+    } else {
+      *pix_music_mask = nullptr;
+    }
+  }
+  pix_closed.destroy();
+  Image pix_nonlines = nullptr;
+  *pix_intersections = nullptr;
+  Image extra_non_hlines = nullptr;
+  if (!v_empty) {
+    // Subtract both line candidates from the source to get definite non-lines.
+    pix_nonlines = pixSubtract(nullptr, src_pix, *pix_vline);
+    if (!h_empty) {
+      pixSubtract(pix_nonlines, pix_nonlines, *pix_hline);
+      // Intersections are a useful indicator for likelihood of being a line.
+      *pix_intersections = *pix_vline & *pix_hline;
+      // Candidate vlines are not hlines (apart from the intersections)
+      // and vice versa.
+      extra_non_hlines = pixSubtract(nullptr, *pix_vline, *pix_intersections);
+    }
+    *pix_non_vline = pixErodeBrick(nullptr, pix_nonlines, kMaxLineResidue, 1);
+    pixSeedfillBinary(*pix_non_vline, *pix_non_vline, pix_nonlines, 8);
+    if (!h_empty) {
+      // Candidate hlines are not vlines.
+      *pix_non_vline |= *pix_hline;
+      pixSubtract(*pix_non_vline, *pix_non_vline, *pix_intersections);
+    }
+    if (!FilterFalsePositives(resolution, *pix_non_vline, *pix_intersections, *pix_vline)) {
+      pix_vline->destroy(); // No candidates left.
+    }
+  } else {
+    // No vertical lines.
+    pix_vline->destroy();
+    *pix_non_vline = nullptr;
+    if (!h_empty) {
+      pix_nonlines = pixSubtract(nullptr, src_pix, *pix_hline);
+    }
+  }
+  if (h_empty) {
+    pix_hline->destroy();
+    *pix_non_hline = nullptr;
+    if (v_empty) {
+      return;
+    }
+  } else {
+    *pix_non_hline = pixErodeBrick(nullptr, pix_nonlines, 1, kMaxLineResidue);
+    pixSeedfillBinary(*pix_non_hline, *pix_non_hline, pix_nonlines, 8);
+    if (extra_non_hlines != nullptr) {
+      *pix_non_hline |= extra_non_hlines;
+      extra_non_hlines.destroy();
+    }
+    if (!FilterFalsePositives(resolution, *pix_non_hline, *pix_intersections, *pix_hline)) {
+      pix_hline->destroy(); // No candidates left.
+    }
+  }
+  if (pixa_display != nullptr) {
+    if (*pix_vline != nullptr) {
+      pixaAddPix(pixa_display, *pix_vline, L_CLONE);
+    }
+    if (*pix_hline != nullptr) {
+      pixaAddPix(pixa_display, *pix_hline, L_CLONE);
+    }
+    if (pix_nonlines != nullptr) {
+      pixaAddPix(pixa_display, pix_nonlines, L_CLONE);
+    }
+    if (*pix_non_vline != nullptr) {
+      pixaAddPix(pixa_display, *pix_non_vline, L_CLONE);
+    }
+    if (*pix_non_hline != nullptr) {
+      pixaAddPix(pixa_display, *pix_non_hline, L_CLONE);
+    }
+    if (*pix_intersections != nullptr) {
+      pixaAddPix(pixa_display, *pix_intersections, L_CLONE);
+    }
+    if (pix_music_mask != nullptr && *pix_music_mask != nullptr) {
+      pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
+    }
+  }
+  pix_nonlines.destroy();
+}
+
+// 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.
+// None of the input pointers may be nullptr, and if *pix_vline is nullptr then
+// the function does nothing.
+static void FindAndRemoveVLines(Image pix_intersections, int *vertical_x,
+                                int *vertical_y, Image *pix_vline, Image pix_non_vline,
+                                Image src_pix, TabVector_LIST *vectors) {
+  if (pix_vline == nullptr || *pix_vline == nullptr) {
+    return;
+  }
+  C_BLOB_LIST line_cblobs;
+  BLOBNBOX_LIST line_bblobs;
+  GetLineBoxes(false, *pix_vline, pix_intersections, &line_cblobs, &line_bblobs);
+  int width = pixGetWidth(src_pix);
+  int height = pixGetHeight(src_pix);
+  ICOORD bleft(0, 0);
+  ICOORD tright(width, height);
+  FindLineVectors(bleft, tright, &line_bblobs, vertical_x, vertical_y, vectors);
+  if (!vectors->empty()) {
+    RemoveUnusedLineSegments(false, &line_bblobs, *pix_vline);
+    SubtractLinesAndResidue(*pix_vline, pix_non_vline, src_pix);
+    ICOORD vertical;
+    vertical.set_with_shrink(*vertical_x, *vertical_y);
+    TabVector::MergeSimilarTabVectors(vertical, vectors, nullptr);
+  } else {
+    pix_vline->destroy();
+  }
+}
+
+// Finds horizontal line objects in pix_hline 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.
+// None of the input pointers may be nullptr, and if *pix_hline is nullptr then
+// the function does nothing.
+static void FindAndRemoveHLines(Image pix_intersections, int vertical_x,
+                                int vertical_y, Image *pix_hline, Image pix_non_hline,
+                                Image src_pix, TabVector_LIST *vectors) {
+  if (pix_hline == nullptr || *pix_hline == nullptr) {
+    return;
+  }
+  C_BLOB_LIST line_cblobs;
+  BLOBNBOX_LIST line_bblobs;
+  GetLineBoxes(true, *pix_hline, pix_intersections, &line_cblobs, &line_bblobs);
+  int width = pixGetWidth(src_pix);
+  int height = pixGetHeight(src_pix);
+  ICOORD bleft(0, 0);
+  ICOORD tright(height, width);
+  FindLineVectors(bleft, tright, &line_bblobs, &vertical_x, &vertical_y, vectors);
+  if (!vectors->empty()) {
+    RemoveUnusedLineSegments(true, &line_bblobs, *pix_hline);
+    SubtractLinesAndResidue(*pix_hline, pix_non_hline, src_pix);
+    ICOORD vertical;
+    vertical.set_with_shrink(vertical_x, vertical_y);
+    TabVector::MergeSimilarTabVectors(vertical, vectors, nullptr);
+    // Iterate the vectors to flip them. x and y were flipped for horizontal
+    // lines, so FindLineVectors can work just with the vertical case.
+    // See GetLineBoxes for more on the flip.
+    TabVector_IT h_it(vectors);
+    for (h_it.mark_cycle_pt(); !h_it.cycled_list(); h_it.forward()) {
+      h_it.data()->XYFlip();
+    }
+  } else {
+    pix_hline->destroy();
+  }
+}
+
+// Finds vertical and horizontal line objects in the given 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.
+// 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.
+void LineFinder::FindAndRemoveLines(int resolution, bool debug, Image pix, int *vertical_x,
+                                    int *vertical_y, Image *pix_music_mask, TabVector_LIST *v_lines,
+                                    TabVector_LIST *h_lines) {
+  if (pix == nullptr || vertical_x == nullptr || vertical_y == nullptr) {
+    tprintf("Error in parameters for LineFinder::FindAndRemoveLines\n");
+    return;
+  }
+  Image pix_vline = nullptr;
+  Image pix_non_vline = nullptr;
+  Image pix_hline = nullptr;
+  Image pix_non_hline = nullptr;
+  Image pix_intersections = nullptr;
+  Pixa *pixa_display = debug ? pixaCreate(0) : nullptr;
+  GetLineMasks(resolution, pix, &pix_vline, &pix_non_vline, &pix_hline, &pix_non_hline,
+               &pix_intersections, pix_music_mask, pixa_display);
+  // Find lines, convert to TabVector_LIST and remove those that are used.
+  FindAndRemoveVLines(pix_intersections, vertical_x, vertical_y, &pix_vline,
+                      pix_non_vline, pix, v_lines);
+  pix_intersections.destroy();
+  if (pix_hline != nullptr) {
+    // Recompute intersections and re-filter false positive h-lines.
+    if (pix_vline != nullptr) {
+      pix_intersections = pix_vline & pix_hline;
+    }
+    if (!FilterFalsePositives(resolution, pix_non_hline, pix_intersections, pix_hline)) {
+      pix_hline.destroy();
+    }
+  }
+  FindAndRemoveHLines(pix_intersections, *vertical_x, *vertical_y, &pix_hline,
+                      pix_non_hline, pix, h_lines);
+  if (pixa_display != nullptr && pix_vline != nullptr) {
+    pixaAddPix(pixa_display, pix_vline, L_CLONE);
+  }
+  if (pixa_display != nullptr && pix_hline != nullptr) {
+    pixaAddPix(pixa_display, pix_hline, L_CLONE);
+  }
+  pix_intersections.destroy();
+  if (pix_vline != nullptr && pix_hline != nullptr) {
+    // Remove joins (intersections) where lines cross, and the residue.
+    // Recalculate the intersections, since some lines have been deleted.
+    pix_intersections = pix_vline & pix_hline;
+    // Fatten up the intersections and seed-fill to get the intersection
+    // residue.
+    Image pix_join_residue = pixDilateBrick(nullptr, pix_intersections, 5, 5);
+    pixSeedfillBinary(pix_join_residue, pix_join_residue, pix, 8);
+    // Now remove the intersection residue.
+    pixSubtract(pix, pix, pix_join_residue);
+    pix_join_residue.destroy();
+  }
+  // Remove any detected music.
+  if (pix_music_mask != nullptr && *pix_music_mask != nullptr) {
+    if (pixa_display != nullptr) {
+      pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
+    }
+    pixSubtract(pix, pix, *pix_music_mask);
+  }
+  if (pixa_display != nullptr) {
+    pixaAddPix(pixa_display, pix, L_CLONE);
+  }
+
+  pix_vline.destroy();
+  pix_non_vline.destroy();
+  pix_hline.destroy();
+  pix_non_hline.destroy();
+  pix_intersections.destroy();
+  if (pixa_display != nullptr) {
+    pixaConvertToPdf(pixa_display, resolution, 1.0f, 0, 0, "LineFinding", "vhlinefinding.pdf");
+    pixaDestroy(&pixa_display);
+  }
+}
+
+} // namespace tesseract.