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linefind.cpp
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1
2 // File: linefind.cpp
3 // Description: Class to find vertical lines in an image and create
4 // a corresponding list of empty blobs.
5 // Author: Ray Smith
6 // Created: Thu Mar 20 09:49:01 PDT 2008
7 //
8 // (C) Copyright 2008, Google Inc.
9 // Licensed under the Apache License, Version 2.0 (the "License");
10 // you may not use this file except in compliance with the License.
11 // You may obtain a copy of the License at
12 // http://www.apache.org/licenses/LICENSE-2.0
13 // Unless required by applicable law or agreed to in writing, software
14 // distributed under the License is distributed on an "AS IS" BASIS,
15 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 // See the License for the specific language governing permissions and
17 // limitations under the License.
18 //
20
21 #ifdef _MSC_VER
22 #pragma warning(disable:4244) // Conversion warnings
23 #endif
24
25 #include "linefind.h"
26 #include "alignedblob.h"
27 #include "tabvector.h"
28 #include "blobbox.h"
29 #include "edgblob.h"
30 // This entire file is dependent upon leptonica. If you don't have it,
31 // then the code doesn't do anything useful.
32 #ifdef HAVE_CONFIG_H
33 #include "config_auto.h"
34 #endif
35 #include "allheaders.h"
36
37 namespace tesseract {
38
40 const int kThinLineFraction = 20;
42 const int kMinLineLengthFraction = 4;
44 const int kCrackSpacing = 100;
46 const int kLineFindGridSize = 50;
47 // Min width of a line in pixels to be considered thick.
48 const int kMinThickLineWidth = 12;
49 // Max size of line residue. (The pixels that fail the long thin opening, and
50 // therefore don't make it to the candidate line mask, but are nevertheless
51 // part of the line.)
52 const int kMaxLineResidue = 6;
53 // Min length in inches of a line segment that exceeds kMinThickLineWidth in
54 // thickness. (Such lines shouldn't break by simple image degradation.)
55 const double kThickLengthMultiple = 0.75;
56 // Max fraction of line box area that can be occupied by non-line pixels.
57 const double kMaxNonLineDensity = 0.25;
58 // Max height of a music stave in inches.
59 const double kMaxStaveHeight = 1.0;
60 // Minimum fraction of pixels in a music rectangle connected to the staves.
61 const double kMinMusicPixelFraction = 0.75;
62
63 // Erases the unused blobs from the line_pix image, taking into account
64 // whether this was a horizontal or vertical line set.
65 static void RemoveUnusedLineSegments(bool horizontal_lines,
66 BLOBNBOX_LIST* line_bblobs,
67 Pix* line_pix) {
68 int height = pixGetHeight(line_pix);
69 BLOBNBOX_IT bbox_it(line_bblobs);
70 for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
71 BLOBNBOX* blob = bbox_it.data();
72 if (blob->left_tab_type() == TT_MAYBE_ALIGNED) {
73 const TBOX& box = blob->bounding_box();
74 Box* pixbox = NULL;
75 if (horizontal_lines) {
76 // Horizontal lines are in tess format and also have x and y flipped
77 // (to use FindVerticalAlignment) so we have to flip x and y and then
78 // convert to Leptonica by height - flipped x (ie the right edge).
79 // See GetLineBoxes for more explanation.
80 pixbox = boxCreate(box.bottom(), height - box.right(),
81 box.height(), box.width());
82
83 } else {
84 // For vertical lines, just flip upside-down to convert to Leptonica.
85 // The y position of the box in Leptonica terms is the distance from
86 // the top of the image to the top of the box.
87 pixbox = boxCreate(box.left(), height - box.top(),
88 box.width(), box.height());
89 }
90 pixClearInRect(line_pix, pixbox);
91 boxDestroy(&pixbox);
92 }
93 }
94 }
95
96 // Helper subtracts the line_pix image from the src_pix, and removes residue
97 // as well by removing components that touch the line, but are not in the
98 // non_line_pix mask. It is assumed that the non_line_pix mask has already
99 // been prepared to required accuracy.
100 static void SubtractLinesAndResidue(Pix* line_pix, Pix* non_line_pix,
101 int resolution, Pix* src_pix) {
102 // First remove the lines themselves.
103 pixSubtract(src_pix, src_pix, line_pix);
104 // Subtract the non-lines from the image to get the residue.
105 Pix* residue_pix = pixSubtract(NULL, src_pix, non_line_pix);
106 // Dilate the lines so they touch the residue.
107 Pix* fat_line_pix = pixDilateBrick(NULL, line_pix, 3, 3);
108 // Seed fill the fat lines to get all the residue.
109 pixSeedfillBinary(fat_line_pix, fat_line_pix, residue_pix, 8);
110 // Subtract the residue from the original image.
111 pixSubtract(src_pix, src_pix, fat_line_pix);
112 pixDestroy(&fat_line_pix);
113 pixDestroy(&residue_pix);
114 }
115
116 // Returns the maximum strokewidth in the given binary image by doubling
117 // the maximum of the distance function.
118 static int MaxStrokeWidth(Pix* pix) {
119 Pix* dist_pix = pixDistanceFunction(pix, 4, 8, L_BOUNDARY_BG);
120 int width = pixGetWidth(dist_pix);
121 int height = pixGetHeight(dist_pix);
122 int wpl = pixGetWpl(dist_pix);
123 l_uint32* data = pixGetData(dist_pix);
124 // Find the maximum value in the distance image.
125 int max_dist = 0;
126 for (int y = 0; y < height; ++y) {
127 for (int x = 0; x < width; ++x) {
128 int pixel = GET_DATA_BYTE(data, x);
129 if (pixel > max_dist)
130 max_dist = pixel;
131 }
132 data += wpl;
133 }
134 pixDestroy(&dist_pix);
135 return max_dist * 2;
136 }
137
138 // Returns the number of components in the intersection_pix touched by line_box.
139 static int NumTouchingIntersections(Box* line_box, Pix* intersection_pix) {
140 if (intersection_pix == NULL) return 0;
141 Pix* rect_pix = pixClipRectangle(intersection_pix, line_box, NULL);
142 Boxa* boxa = pixConnComp(rect_pix, NULL, 8);
143 pixDestroy(&rect_pix);
144 if (boxa == NULL) return false;
145 int result = boxaGetCount(boxa);
146 boxaDestroy(&boxa);
147 return result;
148 }
149
150 // Returns the number of black pixels found in the box made by adding the line
151 // width to both sides of the line bounding box. (Increasing the smallest
152 // dimension of the bounding box.)
153 static int CountPixelsAdjacentToLine(int line_width, Box* line_box,
154 Pix* nonline_pix) {
155 l_int32 x, y, box_width, box_height;
156 boxGetGeometry(line_box, &x, &y, &box_width, &box_height);
157 if (box_width > box_height) {
158 // horizontal line.
159 int bottom = MIN(pixGetHeight(nonline_pix), y + box_height + line_width);
160 y = MAX(0, y - line_width);
161 box_height = bottom - y;
162 } else {
163 // Vertical line.
164 int right = MIN(pixGetWidth(nonline_pix), x + box_width + line_width);
165 x = MAX(0, x - line_width);
166 box_width = right - x;
167 }
168 Box* box = boxCreate(x, y, box_width, box_height);
169 Pix* rect_pix = pixClipRectangle(nonline_pix, box, NULL);
170 boxDestroy(&box);
171 l_int32 result;
172 pixCountPixels(rect_pix, &result, NULL);
173 pixDestroy(&rect_pix);
174 return result;
175 }
176
177 // Helper erases false-positive line segments from the input/output line_pix.
178 // 1. Since thick lines shouldn't really break up, we can eliminate some false
179 // positives by marking segments that are at least kMinThickLineWidth
180 // thickness, yet have a length less than min_thick_length.
181 // 2. Lines that don't have at least 2 intersections with other lines and have
182 // a lot of neighbouring non-lines are probably not lines (perhaps arabic
183 // or Hindi words, or underlines.)
184 // Bad line components are erased from line_pix.
185 // Returns the number of remaining connected components.
186 static int FilterFalsePositives(int resolution, Pix* nonline_pix,
187 Pix* intersection_pix, Pix* line_pix) {
188 int min_thick_length = static_cast<int>(resolution * kThickLengthMultiple);
189 Pixa* pixa = NULL;
190 Boxa* boxa = pixConnComp(line_pix, &pixa, 8);
191 // Iterate over the boxes to remove false positives.
192 int nboxes = boxaGetCount(boxa);
193 int remaining_boxes = nboxes;
194 for (int i = 0; i < nboxes; ++i) {
195 Box* box = boxaGetBox(boxa, i, L_CLONE);
196 l_int32 x, y, box_width, box_height;
197 boxGetGeometry(box, &x, &y, &box_width, &box_height);
198 Pix* comp_pix = pixaGetPix(pixa, i, L_CLONE);
199 int max_width = MaxStrokeWidth(comp_pix);
200 pixDestroy(&comp_pix);
201 bool bad_line = false;
202 // If the length is too short to stand-alone as a line, and the box width
203 // is thick enough, and the stroke width is thick enough it is bad.
204 if (box_width >= kMinThickLineWidth && box_height >= kMinThickLineWidth &&
205 box_width < min_thick_length && box_height < min_thick_length &&
206 max_width > kMinThickLineWidth) {
207 // Too thick for the length.
208 bad_line = true;
209 }
210 if (!bad_line &&
211 (intersection_pix == NULL ||
212 NumTouchingIntersections(box, intersection_pix) < 2)) {
213 // Test non-line density near the line.
214 int nonline_count = CountPixelsAdjacentToLine(max_width, box,
215 nonline_pix);
216 if (nonline_count > box_height * box_width * kMaxNonLineDensity)
217 bad_line = true;
218 }
219 if (bad_line) {
220 // Not a good line.
221 pixClearInRect(line_pix, box);
222 --remaining_boxes;
223 }
224 boxDestroy(&box);
225 }
226 pixaDestroy(&pixa);
227 boxaDestroy(&boxa);
228 return remaining_boxes;
229 }
230
231 // Finds vertical and horizontal line objects in the given pix.
232 // Uses the given resolution to determine size thresholds instead of any
233 // that may be present in the pix.
234 // The output vertical_x and vertical_y contain a sum of the output vectors,
235 // thereby giving the mean vertical direction.
236 // If pix_music_mask != NULL, and music is detected, a mask of the staves
237 // and anything that is connected (bars, notes etc.) will be returned in
238 // pix_music_mask, the mask subtracted from pix, and the lines will not
239 // appear in v_lines or h_lines.
240 // The output vectors are owned by the list and Frozen (cannot refit) by
241 // having no boxes, as there is no need to refit or merge separator lines.
242 // The detected lines are removed from the pix.
243 void LineFinder::FindAndRemoveLines(int resolution, bool debug, Pix* pix,
244 int* vertical_x, int* vertical_y,
245 Pix** pix_music_mask,
246 TabVector_LIST* v_lines,
247 TabVector_LIST* h_lines) {
248 if (pix == NULL || vertical_x == NULL || vertical_y == NULL) {
249 tprintf("Error in parameters for LineFinder::FindAndRemoveLines\n");
250 return;
251 }
252 Pix* pix_vline = NULL;
253 Pix* pix_non_vline = NULL;
254 Pix* pix_hline = NULL;
255 Pix* pix_non_hline = NULL;
256 Pix* pix_intersections = NULL;
257 Pixa* pixa_display = debug ? pixaCreate(0) : NULL;
258 GetLineMasks(resolution, pix, &pix_vline, &pix_non_vline, &pix_hline,
259 &pix_non_hline, &pix_intersections, pix_music_mask,
260 pixa_display);
261 // Find lines, convert to TabVector_LIST and remove those that are used.
262 FindAndRemoveVLines(resolution, pix_intersections, vertical_x, vertical_y,
263 &pix_vline, pix_non_vline, pix, v_lines);
264 if (pix_hline != NULL) {
265 // Recompute intersections and re-filter false positive h-lines.
266 if (pix_vline != NULL)
267 pixAnd(pix_intersections, pix_vline, pix_hline);
268 else
269 pixDestroy(&pix_intersections);
270 if (!FilterFalsePositives(resolution, pix_non_hline, pix_intersections,
271 pix_hline)) {
272 pixDestroy(&pix_hline);
273 }
274 }
275 FindAndRemoveHLines(resolution, pix_intersections, *vertical_x, *vertical_y,
276 &pix_hline, pix_non_hline, pix, h_lines);
277 if (pixa_display != NULL && pix_vline != NULL)
278 pixaAddPix(pixa_display, pix_vline, L_CLONE);
279 if (pixa_display != NULL && pix_hline != NULL)
280 pixaAddPix(pixa_display, pix_hline, L_CLONE);
281 if (pix_vline != NULL && pix_hline != NULL) {
282 // Remove joins (intersections) where lines cross, and the residue.
283 // Recalculate the intersections, since some lines have been deleted.
284 pixAnd(pix_intersections, pix_vline, pix_hline);
285 // Fatten up the intersections and seed-fill to get the intersection
286 // residue.
287 Pix* pix_join_residue = pixDilateBrick(NULL, pix_intersections, 5, 5);
288 pixSeedfillBinary(pix_join_residue, pix_join_residue, pix, 8);
289 // Now remove the intersection residue.
290 pixSubtract(pix, pix, pix_join_residue);
291 pixDestroy(&pix_join_residue);
292 }
293 // Remove any detected music.
294 if (pix_music_mask != NULL && *pix_music_mask != NULL) {
295 if (pixa_display != NULL)
296 pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
297 pixSubtract(pix, pix, *pix_music_mask);
298 }
299 if (pixa_display != NULL)
300 pixaAddPix(pixa_display, pix, L_CLONE);
301
302 pixDestroy(&pix_vline);
303 pixDestroy(&pix_non_vline);
304 pixDestroy(&pix_hline);
305 pixDestroy(&pix_non_hline);
306 pixDestroy(&pix_intersections);
307 if (pixa_display != NULL) {
308 #if LIBLEPT_MINOR_VERSION >= 69 || LIBLEPT_MAJOR_VERSION > 1
309 pixaConvertToPdf(pixa_display, resolution, 1.0f, 0, 0, "LineFinding",
310 "vhlinefinding.pdf");
311 #endif
312 pixaDestroy(&pixa_display);
313 }
314 }
315
316 // Converts the Boxa array to a list of C_BLOB, getting rid of severely
317 // overlapping outlines and those that are children of a bigger one.
318 // The output is a list of C_BLOBs that are owned by the list.
319 // The C_OUTLINEs in the C_BLOBs contain no outline data - just empty
320 // bounding boxes. The Boxa is consumed and destroyed.
321 void LineFinder::ConvertBoxaToBlobs(int image_width, int image_height,
322 Boxa** boxes, C_BLOB_LIST* blobs) {
323 C_OUTLINE_LIST outlines;
324 C_OUTLINE_IT ol_it = &outlines;
325 // Iterate the boxes to convert to outlines.
326 int nboxes = boxaGetCount(*boxes);
327 for (int i = 0; i < nboxes; ++i) {
328 l_int32 x, y, width, height;
329 boxaGetBoxGeometry(*boxes, i, &x, &y, &width, &height);
330 // Make a C_OUTLINE from the leptonica box. This is a bit of a hack,
331 // as there is no outline, just a bounding box, but with some very
332 // small changes to coutln.cpp, it works nicely.
333 ICOORD top_left(x, y);
334 ICOORD bot_right(x + width, y + height);
335 CRACKEDGE startpt;
336 startpt.pos = top_left;
337 C_OUTLINE* outline = new C_OUTLINE(&startpt, top_left, bot_right, 0);
338 ol_it.add_after_then_move(outline);
339 }
340 // Use outlines_to_blobs to convert the outlines to blobs and find
341 // overlapping and contained objects. The output list of blobs in the block
342 // has all the bad ones filtered out and deleted.
343 BLOCK block;
344 ICOORD page_tl(0, 0);
345 ICOORD page_br(image_width, image_height);
346 outlines_to_blobs(&block, page_tl, page_br, &outlines);
347 // Transfer the created blobs to the output list.
348 C_BLOB_IT blob_it(blobs);
349 blob_it.add_list_after(block.blob_list());
350 // The boxes aren't needed any more.
351 boxaDestroy(boxes);
352 }
353
354 // Finds vertical line objects in pix_vline and removes the from src_pix.
355 // Uses the given resolution to determine size thresholds instead of any
356 // that may be present in the pix.
357 // The output vertical_x and vertical_y contain a sum of the output vectors,
358 // thereby giving the mean vertical direction.
359 // The output vectors are owned by the list and Frozen (cannot refit) by
360 // having no boxes, as there is no need to refit or merge separator lines.
361 // If no good lines are found, pix_vline is destroyed.
362 // None of the input pointers may be NULL, and if *pix_vline is NULL then
363 // the function does nothing.
364 void LineFinder::FindAndRemoveVLines(int resolution,
365 Pix* pix_intersections,
366 int* vertical_x, int* vertical_y,
367 Pix** pix_vline, Pix* pix_non_vline,
368 Pix* src_pix, TabVector_LIST* vectors) {
369 if (pix_vline == NULL || *pix_vline == NULL) return;
370 C_BLOB_LIST line_cblobs;
371 BLOBNBOX_LIST line_bblobs;
372 GetLineBoxes(false, *pix_vline, pix_intersections,
373 &line_cblobs, &line_bblobs);
374 int width = pixGetWidth(src_pix);
375 int height = pixGetHeight(src_pix);
376 ICOORD bleft(0, 0);
377 ICOORD tright(width, height);
378 FindLineVectors(bleft, tright, &line_bblobs, vertical_x, vertical_y, vectors);
379 if (!vectors->empty()) {
380 RemoveUnusedLineSegments(false, &line_bblobs, *pix_vline);
381 SubtractLinesAndResidue(*pix_vline, pix_non_vline, resolution, src_pix);
382 ICOORD vertical;
383 vertical.set_with_shrink(*vertical_x, *vertical_y);
384 TabVector::MergeSimilarTabVectors(vertical, vectors, NULL);
385 } else {
386 pixDestroy(pix_vline);
387 }
388 }
389
390 // Finds horizontal line objects in pix_hline and removes them from src_pix.
391 // Uses the given resolution to determine size thresholds instead of any
392 // that may be present in the pix.
393 // The output vertical_x and vertical_y contain a sum of the output vectors,
394 // thereby giving the mean vertical direction.
395 // The output vectors are owned by the list and Frozen (cannot refit) by
396 // having no boxes, as there is no need to refit or merge separator lines.
397 // If no good lines are found, pix_hline is destroyed.
398 // None of the input pointers may be NULL, and if *pix_hline is NULL then
399 // the function does nothing.
400 void LineFinder::FindAndRemoveHLines(int resolution,
401 Pix* pix_intersections,
402 int vertical_x, int vertical_y,
403 Pix** pix_hline, Pix* pix_non_hline,
404 Pix* src_pix, TabVector_LIST* vectors) {
405 if (pix_hline == NULL || *pix_hline == NULL) return;
406 C_BLOB_LIST line_cblobs;
407 BLOBNBOX_LIST line_bblobs;
408 GetLineBoxes(true, *pix_hline, pix_intersections, &line_cblobs, &line_bblobs);
409 int width = pixGetWidth(src_pix);
410 int height = pixGetHeight(src_pix);
411 ICOORD bleft(0, 0);
412 ICOORD tright(height, width);
413 FindLineVectors(bleft, tright, &line_bblobs, &vertical_x, &vertical_y,
414 vectors);
415 if (!vectors->empty()) {
416 RemoveUnusedLineSegments(true, &line_bblobs, *pix_hline);
417 SubtractLinesAndResidue(*pix_hline, pix_non_hline, resolution, src_pix);
418 ICOORD vertical;
419 vertical.set_with_shrink(vertical_x, vertical_y);
420 TabVector::MergeSimilarTabVectors(vertical, vectors, NULL);
421 // Iterate the vectors to flip them. x and y were flipped for horizontal
422 // lines, so FindLineVectors can work just with the vertical case.
423 // See GetLineBoxes for more on the flip.
424 TabVector_IT h_it(vectors);
425 for (h_it.mark_cycle_pt(); !h_it.cycled_list(); h_it.forward()) {
426 h_it.data()->XYFlip();
427 }
428 } else {
429 pixDestroy(pix_hline);
430 }
431 }
432
433 // Finds vertical lines in the given list of BLOBNBOXes. bleft and tright
434 // are the bounds of the image on which the input line_bblobs were found.
435 // The input line_bblobs list is const really.
436 // The output vertical_x and vertical_y are the total of all the vectors.
437 // The output list of TabVector makes no reference to the input BLOBNBOXes.
438 void LineFinder::FindLineVectors(const ICOORD& bleft, const ICOORD& tright,
439 BLOBNBOX_LIST* line_bblobs,
440 int* vertical_x, int* vertical_y,
441 TabVector_LIST* vectors) {
442 BLOBNBOX_IT bbox_it(line_bblobs);
443 int b_count = 0;
444 // Put all the blobs into the grid to find the lines, and move the blobs
445 // to the output lists.
446 AlignedBlob blob_grid(kLineFindGridSize, bleft, tright);
447 for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
448 BLOBNBOX* bblob = bbox_it.data();
449 bblob->set_left_tab_type(TT_MAYBE_ALIGNED);
450 bblob->set_left_rule(bleft.x());
451 bblob->set_right_rule(tright.x());
452 bblob->set_left_crossing_rule(bleft.x());
453 bblob->set_right_crossing_rule(tright.x());
454 blob_grid.InsertBBox(false, true, bblob);
455 ++b_count;
456 }
457 if (b_count == 0)
458 return;
459
460 // Search the entire grid, looking for vertical line vectors.
461 BlobGridSearch lsearch(&blob_grid);
462 BLOBNBOX* bbox;
463 TabVector_IT vector_it(vectors);
464 *vertical_x = 0;
465 *vertical_y = 1;
466 lsearch.StartFullSearch();
467 while ((bbox = lsearch.NextFullSearch()) != NULL) {
468 if (bbox->left_tab_type() == TT_MAYBE_ALIGNED) {
469 const TBOX& box = bbox->bounding_box();
470 if (AlignedBlob::WithinTestRegion(2, box.left(), box.bottom()))
471 tprintf("Finding line vector starting at bbox (%d,%d)\n",
472 box.left(), box.bottom());
473 AlignedBlobParams align_params(*vertical_x, *vertical_y, box.width());
474 TabVector* vector = blob_grid.FindVerticalAlignment(align_params, bbox,
475 vertical_x,
476 vertical_y);
477 if (vector != NULL) {
478 vector->Freeze();
479 vector_it.add_to_end(vector);
480 }
481 }
482 }
483 }
484
485 // Returns a Pix music mask if music is detected.
486 // Any vertical line that has at least 5 intersections in sufficient density
487 // is taken to be a bar. Bars are used as a seed and the entire touching
488 // component is added to the output music mask and subtracted from the lines.
489 // Returns NULL and does minimal work if no music is found.
490 static Pix* FilterMusic(int resolution, Pix* pix_closed,
491 Pix* pix_vline, Pix* pix_hline,
492 l_int32* v_empty, l_int32* h_empty) {
493 int max_stave_height = static_cast<int>(resolution * kMaxStaveHeight);
494 Pix* intersection_pix = pixAnd(NULL, pix_vline, pix_hline);
495 Boxa* boxa = pixConnComp(pix_vline, NULL, 8);
496 // Iterate over the boxes to find music bars.
497 int nboxes = boxaGetCount(boxa);
498 Pix* music_mask = NULL;
499 for (int i = 0; i < nboxes; ++i) {
500 Box* box = boxaGetBox(boxa, i, L_CLONE);
501 l_int32 x, y, box_width, box_height;
502 boxGetGeometry(box, &x, &y, &box_width, &box_height);
503 int joins = NumTouchingIntersections(box, intersection_pix);
504 // Test for the join density being at least 5 per max_stave_height,
505 // ie (joins-1)/box_height >= (5-1)/max_stave_height.
506 if (joins >= 5 && (joins - 1) * max_stave_height >= 4 * box_height) {
507 // This is a music bar. Add to the mask.
508 if (music_mask == NULL)
509 music_mask = pixCreate(pixGetWidth(pix_vline), pixGetHeight(pix_vline),
510 1);
511 pixSetInRect(music_mask, box);
512 }
513 boxDestroy(&box);
514 }
515 boxaDestroy(&boxa);
516 pixDestroy(&intersection_pix);
517 if (music_mask != NULL) {
518 // The mask currently contains just the bars. Use the mask as a seed
519 // and the pix_closed as the mask for a seedfill to get all the
520 // intersecting staves.
521 pixSeedfillBinary(music_mask, music_mask, pix_closed, 8);
522 // Filter out false positives. CCs in the music_mask should be the vast
523 // majority of the pixels in their bounding boxes, as we expect just a
524 // tiny amount of text, a few phrase marks, and crescendo etc left.
525 Boxa* boxa = pixConnComp(music_mask, NULL, 8);
526 // Iterate over the boxes to find music components.
527 int nboxes = boxaGetCount(boxa);
528 for (int i = 0; i < nboxes; ++i) {
529 Box* box = boxaGetBox(boxa, i, L_CLONE);
530 Pix* rect_pix = pixClipRectangle(music_mask, box, NULL);
531 l_int32 music_pixels;
532 pixCountPixels(rect_pix, &music_pixels, NULL);
533 pixDestroy(&rect_pix);
534 rect_pix = pixClipRectangle(pix_closed, box, NULL);
535 l_int32 all_pixels;
536 pixCountPixels(rect_pix, &all_pixels, NULL);
537 pixDestroy(&rect_pix);
538 if (music_pixels < kMinMusicPixelFraction * all_pixels) {
539 // False positive. Delete from the music mask.
540 pixClearInRect(music_mask, box);
541 }
542 boxDestroy(&box);
543 }
544 l_int32 no_remaining_music;
545 boxaDestroy(&boxa);
546 pixZero(music_mask, &no_remaining_music);
547 if (no_remaining_music) {
548 pixDestroy(&music_mask);
549 } else {
550 pixSubtract(pix_vline, pix_vline, music_mask);
551 pixSubtract(pix_hline, pix_hline, music_mask);
552 // We may have deleted all the lines
553 pixZero(pix_vline, v_empty);
554 pixZero(pix_hline, h_empty);
555 }
556 }
557 return music_mask;
558 }
559
560 // Most of the heavy lifting of line finding. Given src_pix and its separate
561 // resolution, returns image masks:
562 // pix_vline candidate vertical lines.
563 // pix_non_vline pixels that didn't look like vertical lines.
564 // pix_hline candidate horizontal lines.
565 // pix_non_hline pixels that didn't look like horizontal lines.
566 // pix_intersections pixels where vertical and horizontal lines meet.
567 // pix_music_mask candidate music staves.
568 // This function promises to initialize all the output (2nd level) pointers,
569 // but any of the returns that are empty will be NULL on output.
570 // None of the input (1st level) pointers may be NULL except pix_music_mask,
571 // which will disable music detection, and pixa_display.
572 void LineFinder::GetLineMasks(int resolution, Pix* src_pix,
573 Pix** pix_vline, Pix** pix_non_vline,
574 Pix** pix_hline, Pix** pix_non_hline,
575 Pix** pix_intersections, Pix** pix_music_mask,
576 Pixa* pixa_display) {
577 int max_line_width = resolution / kThinLineFraction;
578 int min_line_length = resolution / kMinLineLengthFraction;
579 if (pixa_display != NULL) {
580 tprintf("Image resolution = %d, max line width = %d, min length=%d\n",
581 resolution, max_line_width, min_line_length);
582 }
583 int closing_brick = max_line_width / 3;
584
585 // Close up small holes, making it less likely that false alarms are found
586 // in thickened text (as it will become more solid) and also smoothing over
587 // some line breaks and nicks in the edges of the lines.
588 Pix* pix_closed = pixCloseBrick(NULL, src_pix, closing_brick, closing_brick);
589 if (pixa_display != NULL)
590 pixaAddPix(pixa_display, pix_closed, L_CLONE);
591 // Open up with a big box to detect solid areas, which can then be subtracted.
592 // This is very generous and will leave in even quite wide lines.
593 Pix* pix_solid = pixOpenBrick(NULL, pix_closed, max_line_width,
594 max_line_width);
595 if (pixa_display != NULL)
596 pixaAddPix(pixa_display, pix_solid, L_CLONE);
597 Pix* pix_hollow = pixSubtract(NULL, pix_closed, pix_solid);
598 pixDestroy(&pix_solid);
599 // Now open up in both directions independently to find lines of at least
600 // 1 inch/kMinLineLengthFraction in length.
601 if (pixa_display != NULL)
602 pixaAddPix(pixa_display, pix_hollow, L_CLONE);
603 *pix_vline = pixOpenBrick(NULL, pix_hollow, 1, min_line_length);
604 *pix_hline = pixOpenBrick(NULL, pix_hollow, min_line_length, 1);
605 pixDestroy(&pix_hollow);
606 // Lines are sufficiently rare, that it is worth checking for a zero image.
607 l_int32 v_empty = 0;
608 l_int32 h_empty = 0;
609 pixZero(*pix_vline, &v_empty);
610 pixZero(*pix_hline, &h_empty);
611 if (pix_music_mask != NULL) {
612 if (!v_empty && !h_empty) {
613 *pix_music_mask = FilterMusic(resolution, pix_closed,
614 *pix_vline, *pix_hline,
615 &v_empty, &h_empty);
616 } else {
617 *pix_music_mask = NULL;
618 }
619 }
620 pixDestroy(&pix_closed);
621 Pix* pix_nonlines = NULL;
622 *pix_intersections = NULL;
623 Pix* extra_non_hlines = NULL;
624 if (!v_empty) {
625 // Subtract both line candidates from the source to get definite non-lines.
626 pix_nonlines = pixSubtract(NULL, src_pix, *pix_vline);
627 if (!h_empty) {
628 pixSubtract(pix_nonlines, pix_nonlines, *pix_hline);
629 // Intersections are a useful indicator for likelihood of being a line.
630 *pix_intersections = pixAnd(NULL, *pix_vline, *pix_hline);
631 // Candidate vlines are not hlines (apart from the intersections)
632 // and vice versa.
633 extra_non_hlines = pixSubtract(NULL, *pix_vline, *pix_intersections);
634 }
635 *pix_non_vline = pixErodeBrick(NULL, pix_nonlines, kMaxLineResidue, 1);
636 pixSeedfillBinary(*pix_non_vline, *pix_non_vline, pix_nonlines, 8);
637 if (!h_empty) {
638 // Candidate hlines are not vlines.
639 pixOr(*pix_non_vline, *pix_non_vline, *pix_hline);
640 pixSubtract(*pix_non_vline, *pix_non_vline, *pix_intersections);
641 }
642 if (!FilterFalsePositives(resolution, *pix_non_vline, *pix_intersections,
643 *pix_vline))
644 pixDestroy(pix_vline); // No candidates left.
645 } else {
646 // No vertical lines.
647 pixDestroy(pix_vline);
648 *pix_non_vline = NULL;
649 if (!h_empty) {
650 pix_nonlines = pixSubtract(NULL, src_pix, *pix_hline);
651 }
652 }
653 if (h_empty) {
654 pixDestroy(pix_hline);
655 *pix_non_hline = NULL;
656 if (v_empty) {
657 return;
658 }
659 } else {
660 *pix_non_hline = pixErodeBrick(NULL, pix_nonlines, 1, kMaxLineResidue);
661 pixSeedfillBinary(*pix_non_hline, *pix_non_hline, pix_nonlines, 8);
662 if (extra_non_hlines != NULL) {
663 pixOr(*pix_non_hline, *pix_non_hline, extra_non_hlines);
664 pixDestroy(&extra_non_hlines);
665 }
666 if (!FilterFalsePositives(resolution, *pix_non_hline, *pix_intersections,
667 *pix_hline))
668 pixDestroy(pix_hline); // No candidates left.
669 }
670 if (pixa_display != NULL) {
671 if (*pix_vline != NULL) pixaAddPix(pixa_display, *pix_vline, L_CLONE);
672 if (*pix_hline != NULL) pixaAddPix(pixa_display, *pix_hline, L_CLONE);
673 if (pix_nonlines != NULL) pixaAddPix(pixa_display, pix_nonlines, L_CLONE);
674 if (*pix_non_vline != NULL)
675 pixaAddPix(pixa_display, *pix_non_vline, L_CLONE);
676 if (*pix_non_hline != NULL)
677 pixaAddPix(pixa_display, *pix_non_hline, L_CLONE);
678 if (*pix_intersections != NULL)
679 pixaAddPix(pixa_display, *pix_intersections, L_CLONE);
680 if (pix_music_mask != NULL && *pix_music_mask != NULL)
681 pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
682 }
683 pixDestroy(&pix_nonlines);
684 }
685
686 // Returns a list of boxes corresponding to the candidate line segments. Sets
687 // the line_crossings member of the boxes so we can later determin the number
688 // of intersections touched by a full line.
689 void LineFinder::GetLineBoxes(bool horizontal_lines,
690 Pix* pix_lines, Pix* pix_intersections,
691 C_BLOB_LIST* line_cblobs,
692 BLOBNBOX_LIST* line_bblobs) {
693 // Put a single pixel crack in every line at an arbitrary spacing,
694 // so they break up and the bounding boxes can be used to get the
695 // direction accurately enough without needing outlines.
696 int wpl = pixGetWpl(pix_lines);
697 int width = pixGetWidth(pix_lines);
698 int height = pixGetHeight(pix_lines);
699 l_uint32* data = pixGetData(pix_lines);
700 if (horizontal_lines) {
701 for (int y = 0; y < height; ++y, data += wpl) {
702 for (int x = kCrackSpacing; x < width; x += kCrackSpacing) {
703 CLEAR_DATA_BIT(data, x);
704 }
705 }
706 } else {
707 for (int y = kCrackSpacing; y < height; y += kCrackSpacing) {
708 memset(data + wpl * y, 0, wpl * sizeof(*data));
709 }
710 }
711 // Get the individual connected components
712 Boxa* boxa = pixConnComp(pix_lines, NULL, 8);
713 ConvertBoxaToBlobs(width, height, &boxa, line_cblobs);
714 // Make the BLOBNBOXes from the C_BLOBs.
715 C_BLOB_IT blob_it(line_cblobs);
716 BLOBNBOX_IT bbox_it(line_bblobs);
717 for (blob_it.mark_cycle_pt(); !blob_it.cycled_list(); blob_it.forward()) {
718 C_BLOB* cblob = blob_it.data();
719 BLOBNBOX* bblob = new BLOBNBOX(cblob);
720 bbox_it.add_to_end(bblob);
721 // Determine whether the line segment touches two intersections.
722 const TBOX& bbox = bblob->bounding_box();
723 Box* box = boxCreate(bbox.left(), bbox.bottom(),
724 bbox.width(), bbox.height());
725 bblob->set_line_crossings(NumTouchingIntersections(box, pix_intersections));
726 boxDestroy(&box);
727 // Transform the bounding box prior to finding lines. To save writing
728 // two line finders, flip x and y for horizontal lines and re-use the
729 // tab-stop detection code. For vertical lines we still have to flip the
730 // y-coordinates to switch from leptonica coords to tesseract coords.
731 if (horizontal_lines) {
732 // Note that we have Leptonica coords stored in a Tesseract box, so that
733 // bbox.bottom(), being the MIN y coord, is actually the top, so to get
734 // back to Leptonica coords in RemoveUnusedLineSegments, we have to
735 // use height - box.right() as the top, which looks very odd.
736 TBOX new_box(height - bbox.top(), bbox.left(),
737 height - bbox.bottom(), bbox.right());
738 bblob->set_bounding_box(new_box);
739 } else {
740 TBOX new_box(bbox.left(), height - bbox.top(),
741 bbox.right(), height - bbox.bottom());
742 bblob->set_bounding_box(new_box);
743 }
744 }
745 }
746
747 } // namespace tesseract.
748