#endif /* HAVE_CONFIG_H */
#include "allheaders.h"
/* ------------------------------------------------------------
* The sels used here (and their rotated counterparts) are the
* useful 3x3 Sels for thinning. They are defined in sel2.c,
* and the sets are constructed in selaMakeThinSets().
* The notation is based on "Connectivity-preserving morphological
* image transformations", a version of which can be found at
* http://www.leptonica.com/papers/conn.pdf
* ------------------------------------------------------------ */
/*----------------------------------------------------------------*
* CC-preserving thinning *
*----------------------------------------------------------------*/
/*!
* \brief pixaThinConnected()
*
* \param[in] pixas of 1 bpp pix
* \param[in] type L_THIN_FG, L_THIN_BG
* \param[in] connectivity 4 or 8
* \param[in] maxiters max number of iters allowed;
* use 0 to iterate until completion
* \return pixds, or NULL on error
*
*
* Notes:
* (1) See notes in pixThinConnected().
*
*/
PIXA *
pixaThinConnected(PIXA *pixas,
l_int32 type,
l_int32 connectivity,
l_int32 maxiters)
{
l_int32 i, n, d, same;
PIX *pix1, *pix2;
PIXA *pixad;
SELA *sela;
PROCNAME("pixaThinConnected");
if (!pixas)
return (PIXA *)ERROR_PTR("pixas not defined", procName, NULL);
if (type != L_THIN_FG && type != L_THIN_BG)
return (PIXA *)ERROR_PTR("invalid fg/bg type", procName, NULL);
if (connectivity != 4 && connectivity != 8)
return (PIXA *)ERROR_PTR("connectivity not 4 or 8", procName, NULL);
if (maxiters == 0) maxiters = 10000;
pixaVerifyDepth(pixas, &same, &d);
if (d != 1)
return (PIXA *)ERROR_PTR("pix are not all 1 bpp", procName, NULL);
if (connectivity == 4)
sela = selaMakeThinSets(1, 0);
else /* connectivity == 8 */
sela = selaMakeThinSets(5, 0);
n = pixaGetCount(pixas);
pixad = pixaCreate(n);
for (i = 0; i < n; i++) {
pix1 = pixaGetPix(pixas, i, L_CLONE);
pix2 = pixThinConnectedBySet(pix1, type, sela, maxiters);
pixaAddPix(pixad, pix2, L_INSERT);
pixDestroy(&pix1);
}
selaDestroy(&sela);
return pixad;
}
/*!
* \brief pixThinConnected()
*
* \param[in] pixs 1 bpp
* \param[in] type L_THIN_FG, L_THIN_BG
* \param[in] connectivity 4 or 8
* \param[in] maxiters max number of iters allowed;
* use 0 to iterate until completion
* \return pixd, or NULL on error
*
*
* Notes:
* (1) See "Connectivity-preserving morphological image transformations,"
* Dan S. Bloomberg, in SPIE Visual Communications and Image
* Processing, Conference 1606, pp. 320-334, November 1991,
* Boston, MA. A web version is available at
* http://www.leptonica.com/papers/conn.pdf
* (2) This is a simple interface for two of the best iterative
* morphological thinning algorithms, for 4-c.c and 8-c.c.
* Each iteration uses a mixture of parallel operations
* (using several different 3x3 Sels) and serial operations.
* Specifically, each thinning iteration consists of
* four sequential thinnings from each of four directions.
* Each of these thinnings is a parallel composite
* operation, where the union of a set of HMTs are set
* subtracted from the input. For 4-cc thinning, we
* use 3 HMTs in parallel, and for 8-cc thinning we use 4 HMTs.
* (3) A "good" thinning algorithm is one that generates a skeleton
* that is near the medial axis and has neither pruned
* real branches nor left extra dendritic branches.
* (4) Duality between operations on fg and bg require switching
* the connectivity. To thin the foreground, which is the usual
* situation, use type == L_THIN_FG. Thickening the foreground
* is equivalent to thinning the background (type == L_THIN_BG),
* where the alternate connectivity gets preserved.
* For example, to thicken the fg with 2 rounds of iterations
* using 4-c.c., thin the bg using Sels that preserve 8-connectivity:
* Pix *pix = pixThinConnected(pixs, L_THIN_BG, 8, 2);
* (5) This makes and destroys the sela set each time. It's not a large
* overhead, but if you are calling this thousands of times on
* very small images, you can avoid the overhead; e.g.
* Sela *sela = selaMakeThinSets(1, 0); // for 4-c.c.
* Pix *pix = pixThinConnectedBySet(pixs, L_THIN_FG, sela, 0);
* using set 1 for 4-c.c. and set 5 for 8-c.c operations.
*
*/
PIX *
pixThinConnected(PIX *pixs,
l_int32 type,
l_int32 connectivity,
l_int32 maxiters)
{
PIX *pixd;
SELA *sela;
PROCNAME("pixThinConnected");
if (!pixs)
return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
if (pixGetDepth(pixs) != 1)
return (PIX *)ERROR_PTR("pixs not 1 bpp", procName, NULL);
if (type != L_THIN_FG && type != L_THIN_BG)
return (PIX *)ERROR_PTR("invalid fg/bg type", procName, NULL);
if (connectivity != 4 && connectivity != 8)
return (PIX *)ERROR_PTR("connectivity not 4 or 8", procName, NULL);
if (maxiters == 0) maxiters = 10000;
if (connectivity == 4)
sela = selaMakeThinSets(1, 0);
else /* connectivity == 8 */
sela = selaMakeThinSets(5, 0);
pixd = pixThinConnectedBySet(pixs, type, sela, maxiters);
selaDestroy(&sela);
return pixd;
}
/*!
* \brief pixThinConnectedBySet()
*
* \param[in] pixs 1 bpp
* \param[in] type L_THIN_FG, L_THIN_BG
* \param[in] sela of Sels for parallel composite HMTs
* \param[in] maxiters max number of iters allowed;
* use 0 to iterate until completion
* \return pixd, or NULL on error
*
*
* Notes:
* (1) See notes in pixThinConnected().
* (2) This takes a sela representing one of 11 sets of HMT Sels.
* The HMTs from this set are run in parallel and the result
* is OR'd before being subtracted from the source. For each
* iteration, this "parallel" thin is performed four times
* sequentially, for sels rotated by 90 degrees in all four
* directions.
* (3) The "parallel" and "sequential" nomenclature is standard
* in digital filtering. Here, "parallel" operations work on the
* same source (pixd), and accumulate the results in a temp
* image before actually applying them to the source (in this
* case, using an in-place subtraction). "Sequential" operations
* operate directly on the source (pixd) to produce the result
* (in this case, with four sequential thinning operations, one
* from each of four directions).
*
*/
PIX *
pixThinConnectedBySet(PIX *pixs,
l_int32 type,
SELA *sela,
l_int32 maxiters)
{
l_int32 i, j, r, nsels, same;
PIXA *pixahmt;
PIX **pixhmt; /* array owned by pixahmt; do not destroy! */
PIX *pix1, *pix2, *pixd;
SEL *sel, *selr;
PROCNAME("pixThinConnectedBySet");
if (!pixs)
return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
if (pixGetDepth(pixs) != 1)
return (PIX *)ERROR_PTR("pixs not 1 bpp", procName, NULL);
if (type != L_THIN_FG && type != L_THIN_BG)
return (PIX *)ERROR_PTR("invalid fg/bg type", procName, NULL);
if (!sela)
return (PIX *)ERROR_PTR("sela not defined", procName, NULL);
if (maxiters == 0) maxiters = 10000;
/* Set up array of temp pix to hold hmts */
nsels = selaGetCount(sela);
pixahmt = pixaCreate(nsels);
for (i = 0; i < nsels; i++) {
pix1 = pixCreateTemplate(pixs);
pixaAddPix(pixahmt, pix1, L_INSERT);
}
pixhmt = pixaGetPixArray(pixahmt);
if (!pixhmt) {
pixaDestroy(&pixahmt);
return (PIX *)ERROR_PTR("pixhmt array not made", procName, NULL);
}
/* Set up initial image for fg thinning */
if (type == L_THIN_FG)
pixd = pixCopy(NULL, pixs);
else /* bg thinning */
pixd = pixInvert(NULL, pixs);
/* Thin the fg, with up to maxiters iterations */
for (i = 0; i < maxiters; i++) {
pix1 = pixCopy(NULL, pixd); /* test for completion */
for (r = 0; r < 4; r++) { /* over 90 degree rotations of Sels */
for (j = 0; j < nsels; j++) { /* over individual sels in sela */
sel = selaGetSel(sela, j); /* not a copy */
selr = selRotateOrth(sel, r);
pixHMT(pixhmt[j], pixd, selr);
selDestroy(&selr);
if (j > 0)
pixOr(pixhmt[0], pixhmt[0], pixhmt[j]); /* accum result */
}
pixSubtract(pixd, pixd, pixhmt[0]); /* remove result */
}
pixEqual(pixd, pix1, &same);
pixDestroy(&pix1);
if (same) {
/* L_INFO("%d iterations to completion\n", procName, i); */
break;
}
}
/* This is a bit tricky. If we're thickening the foreground, then
* we get a fg border of thickness equal to the number of
* iterations. This border is connected to all components that
* were initially touching the border, but as it grows, it does
* not touch other growing components -- it leaves a 1 pixel wide
* background between it and the growing components, and that
* thin background prevents the components from growing further.
* This border can be entirely removed as follows:
* (1) Subtract the original (unthickened) image pixs from the
* thickened image. This removes the pixels that were originally
* touching the border.
* (2) Get all remaining pixels that are connected to the border.
* (3) Remove those pixels from the thickened image. */
if (type == L_THIN_BG) {
pixInvert(pixd, pixd); /* finish with duality */
pix1 = pixSubtract(NULL, pixd, pixs);
pix2 = pixExtractBorderConnComps(pix1, 4);
pixSubtract(pixd, pixd, pix2);
pixDestroy(&pix1);
pixDestroy(&pix2);
}
pixaDestroy(&pixahmt);
return pixd;
}
/*!
* \brief selaMakeThinSets()
*
* \param[in] index into specific sets
* \param[in] debug 1 to output display of sela
* \return sela, or NULL on error
*
*
* Notes:
* (1) These are specific sets of HMTs to be used in parallel for
* for thinning from each of four directions.
* (2) The sets are indexed as follows:
* For thinning (e.g., run to completion):
* index = 1 sel_4_1, sel_4_2, sel_4_3
* index = 2 sel_4_1, sel_4_5, sel_4_6
* index = 3 sel_4_1, sel_4_7, sel_4_7_rot
* index = 4 sel_48_1, sel_48_1_rot, sel_48_2
* index = 5 sel_8_2, sel_8_3, sel_8_5, sel_8_6
* index = 6 sel_8_2, sel_8_3, sel_48_2
* index = 7 sel_8_1, sel_8_5, sel_8_6
* index = 8 sel_8_2, sel_8_3, sel_8_8, sel_8_9
* index = 9 sel_8_5, sel_8_6, sel_8_7, sel_8_7_rot
* For thickening (e.g., just a few iterations):
* index = 10 sel_4_2, sel_4_3
* index = 11 sel_8_4
* (3) For a very smooth skeleton, use set 1 for 4 connected and
* set 5 for 8 connected thins.
*
*/
SELA *
selaMakeThinSets(l_int32 index,
l_int32 debug)
{
SEL *sel;
SELA *sela1, *sela2, *sela3;
PROCNAME("selaMakeThinSets");
if (index < 1 || index > 11)
return (SELA *)ERROR_PTR("invalid index", procName, NULL);
sela2 = selaCreate(4);
switch(index)
{
case 1:
sela1 = sela4ccThin(NULL);
selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_3", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 2:
sela1 = sela4ccThin(NULL);
selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_5", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_6", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 3:
sela1 = sela4ccThin(NULL);
selaFindSelByName(sela1, "sel_4_1", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_7", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
sel = selRotateOrth(sel, 1);
selaAddSel(sela2, sel, "sel_4_7_rot", L_INSERT);
break;
case 4:
sela1 = sela4and8ccThin(NULL);
selaFindSelByName(sela1, "sel_48_1", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
sel = selRotateOrth(sel, 1);
selaAddSel(sela2, sel, "sel_48_1_rot", L_INSERT);
selaFindSelByName(sela1, "sel_48_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 5:
sela1 = sela8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 6:
sela1 = sela8ccThin(NULL);
sela3 = sela4and8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela3, "sel_48_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaDestroy(&sela3);
break;
case 7:
sela1 = sela8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_1", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 8:
sela1 = sela8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_3", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_8", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_9", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 9:
sela1 = sela8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_5", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_6", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_8_7", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
sel = selRotateOrth(sel, 1);
selaAddSel(sela2, sel, "sel_8_7_rot", L_INSERT);
break;
case 10: /* thicken for this one; use just a few iterations */
sela1 = sela4ccThin(NULL);
selaFindSelByName(sela1, "sel_4_2", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
selaFindSelByName(sela1, "sel_4_3", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
case 11: /* thicken for this one; use just a few iterations */
sela1 = sela8ccThin(NULL);
selaFindSelByName(sela1, "sel_8_4", NULL, &sel);
selaAddSel(sela2, sel, NULL, L_COPY);
break;
}
/* Optionally display the sel set */
if (debug) {
PIX *pix1;
char buf[32];
lept_mkdir("/lept/sels");
pix1 = selaDisplayInPix(sela2, 35, 3, 15, 4);
snprintf(buf, sizeof(buf), "/tmp/lept/sels/set%d.png", index);
pixWrite(buf, pix1, IFF_PNG);
pixDisplay(pix1, 100, 100);
pixDestroy(&pix1);
}
selaDestroy(&sela1);
return sela2;
}