1 /*====================================================================*
2 - Copyright (C) 2001 Leptonica. All rights reserved.
3 -
4 - Redistribution and use in source and binary forms, with or without
5 - modification, are permitted provided that the following conditions
6 - are met:
7 - 1. Redistributions of source code must retain the above copyright
8 - notice, this list of conditions and the following disclaimer.
9 - 2. Redistributions in binary form must reproduce the above
10 - copyright notice, this list of conditions and the following
11 - disclaimer in the documentation and/or other materials
12 - provided with the distribution.
13 -
14 - THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
15 - ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
16 - LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
17 - A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ANY
18 - CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
19 - EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
20 - PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
21 - PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
22 - OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
23 - NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
24 - SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 *====================================================================*/
26
27 /*!
28 * \file ccthin.c
29 * <pre>
30 *
31 * PIXA *pixaThinConnected()
32 * PIX *pixThinConnected()
33 * PIX *pixThinConnectedBySet()
34 * SELA *selaMakeThinSets()
35 * </pre>
36 */
37
38 #include "allheaders.h"
39
40 /* ------------------------------------------------------------
41 * The sels used here (and their rotated counterparts) are the
42 * useful 3x3 Sels for thinning. They are defined in sel2.c,
43 * and the sets are constructed in selaMakeThinSets().
44 * The notation is based on "Connectivity-preserving morphological
45 * image transformations", a version of which can be found at
46 * http://www.leptonica.com/papers/conn.pdf
47 * ------------------------------------------------------------ */
48
49 /*----------------------------------------------------------------*
50 * CC-preserving thinning *
51 *----------------------------------------------------------------*/
52 /*!
53 * \brief pixaThinConnected()
54 *
55 * \param[in] pixas of 1 bpp pix
56 * \param[in] type L_THIN_FG, L_THIN_BG
57 * \param[in] connectivity 4 or 8
58 * \param[in] maxiters max number of iters allowed; use 0 to iterate
59 * until completion
60 * \return pixds, or NULL on error
61 *
62 * <pre>
63 * Notes:
64 * (1) See notes in pixThinConnected().
65 * </pre>
66 */
67 PIXA *
pixaThinConnected(PIXA * pixas,l_int32 type,l_int32 connectivity,l_int32 maxiters)68 pixaThinConnected(PIXA *pixas,
69 l_int32 type,
70 l_int32 connectivity,
71 l_int32 maxiters)
72 {
73 l_int32 i, n, d, same;
74 PIX *pix1, *pix2;
75 PIXA *pixad;
76 SELA *sela;
77
78 PROCNAME("pixaThinConnected");
79
80 if (!pixas)
81 return (PIXA *)ERROR_PTR("pixas not defined", procName, NULL);
82 if (type != L_THIN_FG && type != L_THIN_BG)
83 return (PIXA *)ERROR_PTR("invalid fg/bg type", procName, NULL);
84 if (connectivity != 4 && connectivity != 8)
85 return (PIXA *)ERROR_PTR("connectivity not 4 or 8", procName, NULL);
86 if (maxiters == 0) maxiters = 10000;
87
88 pixaVerifyDepth(pixas, &same, &d);
89 if (d != 1)
90 return (PIXA *)ERROR_PTR("pix are not all 1 bpp", procName, NULL);
91
92 if (connectivity == 4)
93 sela = selaMakeThinSets(1, 0);
94 else /* connectivity == 8 */
95 sela = selaMakeThinSets(5, 0);
96
97 n = pixaGetCount(pixas);
98 pixad = pixaCreate(n);
99 for (i = 0; i < n; i++) {
100 pix1 = pixaGetPix(pixas, i, L_CLONE);
101 pix2 = pixThinConnectedBySet(pix1, type, sela, maxiters);
102 pixaAddPix(pixad, pix2, L_INSERT);
103 pixDestroy(&pix1);
104 }
105
106 selaDestroy(&sela);
107 return pixad;
108 }
109
110
111 /*!
112 * \brief pixThinConnected()
113 *
114 * \param[in] pixs 1 bpp
115 * \param[in] type L_THIN_FG, L_THIN_BG
116 * \param[in] connectivity 4 or 8
117 * \param[in] maxiters max number of iters allowed; use 0 to iterate
118 * until completion
119 * \return pixd, or NULL on error
120 *
121 * <pre>
122 * Notes:
123 * (1) See "Connectivity-preserving morphological image transformations,"
124 * Dan S. Bloomberg, in SPIE Visual Communications and Image
125 * Processing, Conference 1606, pp. 320-334, November 1991,
126 * Boston, MA. A web version is available at
127 * http://www.leptonica.com/papers/conn.pdf
128 * (2) This is a simple interface for two of the best iterative
129 * morphological thinning algorithms, for 4-c.c and 8-c.c.
130 * Each iteration uses a mixture of parallel operations
131 * (using several different 3x3 Sels) and serial operations.
132 * Specifically, each thinning iteration consists of
133 * four sequential thinnings from each of four directions.
134 * Each of these thinnings is a parallel composite
135 * operation, where the union of a set of HMTs are set
136 * subtracted from the input. For 4-cc thinning, we
137 * use 3 HMTs in parallel, and for 8-cc thinning we use 4 HMTs.
138 * (3) A "good" thinning algorithm is one that generates a skeleton
139 * that is near the medial axis and has neither pruned
140 * real branches nor left extra dendritic branches.
141 * (4) Duality between operations on fg and bg require switching
142 * the connectivity. To thin the foreground, which is the usual
143 * situation, use type == L_THIN_FG. Thickening the foreground
144 * is equivalent to thinning the background (type == L_THIN_BG),
145 * where the alternate connectivity gets preserved.
146 * For example, to thicken the fg with 2 rounds of iterations
147 * using 4-c.c., thin the bg using Sels that preserve 8-connectivity:
148 * Pix *pix = pixThinConnected(pixs, L_THIN_BG, 8, 2);
149 * (5) This makes and destroys the sela set each time. It's not a large
150 * overhead, but if you are calling this thousands of times on
151 * very small images, you can avoid the overhead; e.g.
152 * Sela *sela = selaMakeThinSets(1, 0); // for 4-c.c.
153 * Pix *pix = pixThinConnectedBySet(pixs, L_THIN_FG, sela, 0);
154 * using set 1 for 4-c.c. and set 5 for 8-c.c operations.
155 * </pre>
156 */
157 PIX *
pixThinConnected(PIX * pixs,l_int32 type,l_int32 connectivity,l_int32 maxiters)158 pixThinConnected(PIX *pixs,
159 l_int32 type,
160 l_int32 connectivity,
161 l_int32 maxiters)
162 {
163 PIX *pixd;
164 SELA *sela;
165
166 PROCNAME("pixThinConnected");
167
168 if (!pixs)
169 return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
170 if (pixGetDepth(pixs) != 1)
171 return (PIX *)ERROR_PTR("pixs not 1 bpp", procName, NULL);
172 if (type != L_THIN_FG && type != L_THIN_BG)
173 return (PIX *)ERROR_PTR("invalid fg/bg type", procName, NULL);
174 if (connectivity != 4 && connectivity != 8)
175 return (PIX *)ERROR_PTR("connectivity not 4 or 8", procName, NULL);
176 if (maxiters == 0) maxiters = 10000;
177
178 if (connectivity == 4)
179 sela = selaMakeThinSets(1, 0);
180 else /* connectivity == 8 */
181 sela = selaMakeThinSets(5, 0);
182
183 pixd = pixThinConnectedBySet(pixs, type, sela, maxiters);
184
185 selaDestroy(&sela);
186 return pixd;
187 }
188
189
190 /*!
191 * \brief pixThinConnectedBySet()
192 *
193 * \param[in] pixs 1 bpp
194 * \param[in] type L_THIN_FG, L_THIN_BG
195 * \param[in] sela of Sels for parallel composite HMTs
196 * \param[in] maxiters max number of iters allowed; use 0 to iterate
197 * until completion
198 * \return pixd, or NULL on error
199 *
200 * <pre>
201 * Notes:
202 * (1) See notes in pixThinConnected().
203 * (2) This takes a sela representing one of 11 sets of HMT Sels.
204 * The HMTs from this set are run in parallel and the result
205 * is OR'd before being subtracted from the source. For each
206 * iteration, this "parallel" thin is performed four times
207 * sequentially, for sels rotated by 90 degrees in all four
208 * directions.
209 * (3) The "parallel" and "sequential" nomenclature is standard
210 * in digital filtering. Here, "parallel" operations work on the
211 * same source (pixd), and accumulate the results in a temp
212 * image before actually applying them to the source (in this
213 * case, using an in-place subtraction). "Sequential" operations
214 * operate directly on the source (pixd) to produce the result
215 * (in this case, with four sequential thinning operations, one
216 * from each of four directions).
217 * </pre>
218 */
219 PIX *
pixThinConnectedBySet(PIX * pixs,l_int32 type,SELA * sela,l_int32 maxiters)220 pixThinConnectedBySet(PIX *pixs,
221 l_int32 type,
222 SELA *sela,
223 l_int32 maxiters)
224 {
225 l_int32 i, j, r, nsels, same;
226 PIXA *pixahmt;
227 PIX **pixhmt; /* array owned by pixahmt; do not destroy! */
228 PIX *pix1, *pix2, *pixd;
229 SEL *sel, *selr;
230
231 PROCNAME("pixThinConnectedBySet");
232
233 if (!pixs)
234 return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
235 if (pixGetDepth(pixs) != 1)
236 return (PIX *)ERROR_PTR("pixs not 1 bpp", procName, NULL);
237 if (type != L_THIN_FG && type != L_THIN_BG)
238 return (PIX *)ERROR_PTR("invalid fg/bg type", procName, NULL);
239 if (!sela)
240 return (PIX *)ERROR_PTR("sela not defined", procName, NULL);
241 if (maxiters == 0) maxiters = 10000;
242
243 /* Set up array of temp pix to hold hmts */
244 nsels = selaGetCount(sela);
245 pixahmt = pixaCreate(nsels);
246 for (i = 0; i < nsels; i++) {
247 pix1 = pixCreateTemplate(pixs);
248 pixaAddPix(pixahmt, pix1, L_INSERT);
249 }
250 pixhmt = pixaGetPixArray(pixahmt);
251 if (!pixhmt) {
252 pixaDestroy(&pixahmt);
253 return (PIX *)ERROR_PTR("pixhmt array not made", procName, NULL);
254 }
255
256 /* Set up initial image for fg thinning */
257 if (type == L_THIN_FG)
258 pixd = pixCopy(NULL, pixs);
259 else /* bg thinning */
260 pixd = pixInvert(NULL, pixs);
261
262 /* Thin the fg, with up to maxiters iterations */
263 for (i = 0; i < maxiters; i++) {
264 pix1 = pixCopy(NULL, pixd); /* test for completion */
265 for (r = 0; r < 4; r++) { /* over 90 degree rotations of Sels */
266 for (j = 0; j < nsels; j++) { /* over individual sels in sela */
267 sel = selaGetSel(sela, j); /* not a copy */
268 selr = selRotateOrth(sel, r);
269 pixHMT(pixhmt[j], pixd, selr);
270 selDestroy(&selr);
271 if (j > 0)
272 pixOr(pixhmt[0], pixhmt[0], pixhmt[j]); /* accum result */
273 }
274 pixSubtract(pixd, pixd, pixhmt[0]); /* remove result */
275 }
276 pixEqual(pixd, pix1, &same);
277 pixDestroy(&pix1);
278 if (same) {
279 /* L_INFO("%d iterations to completion\n", procName, i); */
280 break;
281 }
282 }
283
284 /* This is a bit tricky. If we're thickening the foreground, then
285 * we get a fg border of thickness equal to the number of
286 * iterations. This border is connected to all components that
287 * were initially touching the border, but as it grows, it does
288 * not touch other growing components -- it leaves a 1 pixel wide
289 * background between it and the growing components, and that
290 * thin background prevents the components from growing further.
291 * This border can be entirely removed as follows:
292 * (1) Subtract the original (unthickened) image pixs from the
293 * thickened image. This removes the pixels that were originally
294 * touching the border.
295 * (2) Get all remaining pixels that are connected to the border.
296 * (3) Remove those pixels from the thickened image. */
297 if (type == L_THIN_BG) {
298 pixInvert(pixd, pixd); /* finish with duality */
299 pix1 = pixSubtract(NULL, pixd, pixs);
300 pix2 = pixExtractBorderConnComps(pix1, 4);
301 pixSubtract(pixd, pixd, pix2);
302 pixDestroy(&pix1);
303 pixDestroy(&pix2);
304 }
305
306 pixaDestroy(&pixahmt);
307 return pixd;
308 }
309
310
311 /*!
312 * \brief selaMakeThinSets()
313 *
314 * \param[in] index into specific sets
315 * \param[in] debug 1 to output display of sela
316 * \return sela, or NULL on error
317 *
318 * <pre>
319 * Notes:
320 * (1) These are specific sets of HMTs to be used in parallel for
321 * for thinning from each of four directions.
322 * (2) The sets are indexed as follows:
323 * For thinning (e.g., run to completion):
324 * index = 1 sel_4_1, sel_4_2, sel_4_3
325 * index = 2 sel_4_1, sel_4_5, sel_4_6
326 * index = 3 sel_4_1, sel_4_7, sel_4_7_rot
327 * index = 4 sel_48_1, sel_48_1_rot, sel_48_2
328 * index = 5 sel_8_2, sel_8_3, sel_8_5, sel_8_6
329 * index = 6 sel_8_2, sel_8_3, sel_48_2
330 * index = 7 sel_8_1, sel_8_5, sel_8_6
331 * index = 8 sel_8_2, sel_8_3, sel_8_8, sel_8_9
332 * index = 9 sel_8_5, sel_8_6, sel_8_7, sel_8_7_rot
333 * For thickening (e.g., just a few iterations):
334 * index = 10 sel_4_2, sel_4_3
335 * index = 11 sel_8_4
336 * (3) For a very smooth skeleton, use set 1 for 4 connected and
337 * set 5 for 8 connected thins.
338 * </pre>
339 */
340 SELA *
selaMakeThinSets(l_int32 index,l_int32 debug)341 selaMakeThinSets(l_int32 index,
342 l_int32 debug)
343 {
344 SEL *sel;
345 SELA *sela1, *sela2, *sela3;
346
347 PROCNAME("selaMakeThinSets");
348
349 if (index < 1 || index > 11)
350 return (SELA *)ERROR_PTR("invalid index", procName, NULL);
351
352 sela2 = selaCreate(4);
353 switch(index)
354 {
355 case 1:
356 sela1 = sela4ccThin(NULL);
357 selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
358 selaAddSel(sela2, sel, NULL, L_COPY);
359 selaFindSelByName(sela1, "sel_4_2", NULL, &sel);
360 selaAddSel(sela2, sel, NULL, L_COPY);
361 selaFindSelByName(sela1, "sel_4_3", NULL, &sel);
362 selaAddSel(sela2, sel, NULL, L_COPY);
363 break;
364 case 2:
365 sela1 = sela4ccThin(NULL);
366 selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
367 selaAddSel(sela2, sel, NULL, L_COPY);
368 selaFindSelByName(sela1, "sel_4_5", NULL, &sel);
369 selaAddSel(sela2, sel, NULL, L_COPY);
370 selaFindSelByName(sela1, "sel_4_6", NULL, &sel);
371 selaAddSel(sela2, sel, NULL, L_COPY);
372 break;
373 case 3:
374 sela1 = sela4ccThin(NULL);
375 selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
376 selaAddSel(sela2, sel, NULL, L_COPY);
377 selaFindSelByName(sela1, "sel_4_7", NULL, &sel);
378 selaAddSel(sela2, sel, NULL, L_COPY);
379 sel = selRotateOrth(sel, 1);
380 selaAddSel(sela2, sel, "sel_4_7_rot", L_INSERT);
381 break;
382 case 4:
383 sela1 = sela4and8ccThin(NULL);
384 selaFindSelByName(sela1, "sel_48_1", NULL, &sel);
385 selaAddSel(sela2, sel, NULL, L_COPY);
386 sel = selRotateOrth(sel, 1);
387 selaAddSel(sela2, sel, "sel_48_1_rot", L_INSERT);
388 selaFindSelByName(sela1, "sel_48_2", NULL, &sel);
389 selaAddSel(sela2, sel, NULL, L_COPY);
390 break;
391 case 5:
392 sela1 = sela8ccThin(NULL);
393 selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
394 selaAddSel(sela2, sel, NULL, L_COPY);
395 selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
396 selaAddSel(sela2, sel, NULL, L_COPY);
397 selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
398 selaAddSel(sela2, sel, NULL, L_COPY);
399 selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
400 selaAddSel(sela2, sel, NULL, L_COPY);
401 break;
402 case 6:
403 sela1 = sela8ccThin(NULL);
404 sela3 = sela4and8ccThin(NULL);
405 selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
406 selaAddSel(sela2, sel, NULL, L_COPY);
407 selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
408 selaAddSel(sela2, sel, NULL, L_COPY);
409 selaFindSelByName(sela3, "sel_48_2", NULL, &sel);
410 selaAddSel(sela2, sel, NULL, L_COPY);
411 selaDestroy(&sela3);
412 break;
413 case 7:
414 sela1 = sela8ccThin(NULL);
415 selaFindSelByName(sela1, "sel_8_1", NULL, &sel);
416 selaAddSel(sela2, sel, NULL, L_COPY);
417 selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
418 selaAddSel(sela2, sel, NULL, L_COPY);
419 selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
420 selaAddSel(sela2, sel, NULL, L_COPY);
421 break;
422 case 8:
423 sela1 = sela8ccThin(NULL);
424 selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
425 selaAddSel(sela2, sel, NULL, L_COPY);
426 selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
427 selaAddSel(sela2, sel, NULL, L_COPY);
428 selaFindSelByName(sela1, "sel_8_8", NULL, &sel);
429 selaAddSel(sela2, sel, NULL, L_COPY);
430 selaFindSelByName(sela1, "sel_8_9", NULL, &sel);
431 selaAddSel(sela2, sel, NULL, L_COPY);
432 break;
433 case 9:
434 sela1 = sela8ccThin(NULL);
435 selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
436 selaAddSel(sela2, sel, NULL, L_COPY);
437 selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
438 selaAddSel(sela2, sel, NULL, L_COPY);
439 selaFindSelByName(sela1, "sel_8_7", NULL, &sel);
440 selaAddSel(sela2, sel, NULL, L_COPY);
441 sel = selRotateOrth(sel, 1);
442 selaAddSel(sela2, sel, "sel_8_7_rot", L_INSERT);
443 break;
444 case 10: /* thicken for this one; use just a few iterations */
445 sela1 = sela4ccThin(NULL);
446 selaFindSelByName(sela1, "sel_4_2", NULL, &sel);
447 selaAddSel(sela2, sel, NULL, L_COPY);
448 selaFindSelByName(sela1, "sel_4_3", NULL, &sel);
449 selaAddSel(sela2, sel, NULL, L_COPY);
450 break;
451 case 11: /* thicken for this one; use just a few iterations */
452 sela1 = sela8ccThin(NULL);
453 selaFindSelByName(sela1, "sel_8_4", NULL, &sel);
454 selaAddSel(sela2, sel, NULL, L_COPY);
455 break;
456 }
457
458 /* Optionally display the sel set */
459 if (debug) {
460 PIX *pix1;
461 char buf[32];
462 lept_mkdir("/lept/sels");
463 pix1 = selaDisplayInPix(sela2, 35, 3, 15, 4);
464 snprintf(buf, sizeof(buf), "/tmp/lept/sels/set%d.png", index);
465 pixWrite(buf, pix1, IFF_PNG);
466 pixDisplay(pix1, 100, 100);
467 pixDestroy(&pix1);
468 }
469
470 selaDestroy(&sela1);
471 return sela2;
472 }
473
474