/*====================================================================*
- Copyright (C) 2001 Leptonica. All rights reserved.
- This software is distributed in the hope that it will be
- useful, but with NO WARRANTY OF ANY KIND.
- No author or distributor accepts responsibility to anyone for the
- consequences of using this software, or for whether it serves any
- particular purpose or works at all, unless he or she says so in
- writing. Everyone is granted permission to copy, modify and
- redistribute this source code, for commercial or non-commercial
- purposes, with the following restrictions: (1) the origin of this
- source code must not be misrepresented; (2) modified versions must
- be plainly marked as such; and (3) this notice may not be removed
- or altered from any source or modified source distribution.
*====================================================================*/
/*
* flipdetect.c
*
* Page orientation detection (pure rotation by 90 degree increments):
* l_int32 pixOrientDetect()
* l_int32 makeOrientDecision()
* l_int32 pixUpDownDetect()
* l_int32 pixUpDownDetectGeneral()
* l_int32 pixOrientDetectDwa()
* l_int32 pixUpDownDetectDwa()
* l_int32 pixUpDownDetectGeneralDwa()
*
* Page mirror detection (flip 180 degrees about line in plane of image):
* l_int32 pixMirrorDetect()
* l_int32 pixMirrorDetectDwa()
*
* Static debug helper
* void pixDebugFlipDetect()
*
* ===================================================================
*
* Page transformation detection:
*
* Once a page is deskewed, there are 8 possible states that it
* can be in, shown symbolically below. Suppose state 0 is correct.
*
* 0: correct 1 2 3
* +------+ +------+ +------+ +------+
* | **** | | * | | **** | | * |
* | * | | * | | * | | * |
* | * | | **** | | * | | **** |
* +------+ +------+ +------+ +------+
*
* 4 5 6 7
* +-----+ +-----+ +-----+ +-----+
* | *** | | * | | *** | | * |
* | * | | * | | * | | * |
* | * | | * | | * | | * |
* | * | | *** | | * | | *** |
* +-----+ +-----+ +-----+ +-----+
*
* Each of the other seven can be derived from state 0 by applying some
* combination of a 90 degree clockwise rotation, a flip about
* a horizontal line, and a flip about a vertical line,
* all abbreviated as:
* R = Rotation (about a line perpendicular to the image)
* H = Horizontal flip (about a vertical line in the plane of the image)
* V = Vertical flip (about a horizontal line in the plane of the image)
*
* We get these transformations:
* RHV
* 000 -> 0
* 001 -> 1
* 010 -> 2
* 011 -> 3
* 100 -> 4
* 101 -> 5
* 110 -> 6
* 111 -> 7
*
* Note that in four of these, the sum of H and V is 1 (odd).
* For these four, we have a change in parity (handedness) of
* the image, and the transformation cannot be performed by
* rotation about a vertical line out of the page. Under
* rotation R, the set of 8 transformations decomposes into
* two subgroups linking {0, 3, 4, 7} and {1, 2, 5, 6} independently.
*
* pixOrientDetect*() tests for a pure rotation (0, 90, 180, 270 degrees).
* It doesn't change parity.
*
* pixMirrorDetect*() tests for a horizontal flip about the vertical axis.
* It changes parity.
*
* The landscape/portrait rotation can be detected in two ways:
*
* (1) Compute the deskew confidence for an image segment,
* both as is and rotated 90 degrees (see skew.c).
*
* (2) Compute the ascender/descender signal for the image,
* both as is and rotated 90 degrees (implemented here).
*
* The ascender/descender signal is useful for determining text
* orientation in Roman alphabets because the incidence of letters
* with straight-line ascenders (b, d, h, k, l, <t>) outnumber
* those with descenders (<g>, p, q). The letters <t> and <g>
* will respond variably to the filter, depending on the type face.
*
* What about the mirror image situations? These aren't common
* unless you're dealing with film, for example.
* But you can reliably test if the image has undergone a
* parity-changing flip once about some axis in the plane
* of the image, using pixMirrorDetect*(). This works ostensibly by
* counting the number of characters with ascenders that
* stick out to the left and right of the ascender. Characters
* that are not mirror flipped are more likely to extend to the
* right (b, h, k) than to the left (d). Of course, that is for
* text that is rightside-up. So before you apply the mirror
* test, it is necessary to insure that the text has the ascenders
* going up, and not down or to the left or right. But here's
* what *really* happens. It turns out that the pre-filtering before
* the hit-miss transform (HMT) is crucial, and surprisingly, when
* the pre-filtering is chosen to generate a large signal, the majority
* of the signal comes from open regions of common lower-case
* letters such as 'e', 'c' and 'f'.
*
* All operations are given in two implementations whose results are
* identical: rasterop morphology and dwa morphology. The dwa
* implementations are between 2x and 3x faster.
*
* The set of operations you actually use depends on your prior knowledge:
*
* (1) If the page is known to be either rightside-up or upside-down, use
* either pixOrientDetect*() with pleftconf = NULL, or
* pixUpDownDetect*(). [The '*' refers to either the rasterop
* or dwa versions.]
*
* (2) If any of the four orientations are possible, use pixOrientDetect*().
*
* (3) If the text is horizontal and rightside-up, the only remaining
* degree of freedom is a left-right mirror flip: use
* pixMirrorDetect*().
*
* (4) If you have a relatively large amount of numbers on the page,
* us the slower pixUpDownDetectGeneral().
*
* We summarize the full orientation and mirror flip detection process:
*
* (1) First determine which of the four 90 degree rotations
* causes the text to be rightside-up. This can be done
* with either skew confidence or the pixOrientDetect*()
* signals. For the latter, see the table for pixOrientDetect().
*
* (2) Then, with ascenders pointing up, apply pixMirrorDetect*().
* In the normal situation the confidence confidence will be
* large and positive. However, if mirror flipped, the
* confidence will be large and negative.
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "allheaders.h"
/* Sels for pixOrientDetect() and pixMirrorDetect() */
static const char *textsel1 = "x oo "
"x oOo "
"x o "
"x "
"xxxxxx";
static const char *textsel2 = " oo x"
" oOo x"
" o x"
" x"
"xxxxxx";
static const char *textsel3 = "xxxxxx"
"x "
"x o "
"x oOo "
"x oo ";
static const char *textsel4 = "xxxxxx"
" x"
" o x"
" oOo x"
" oo x";
/* Parameters for determining orientation */
static const l_int32 DEFAULT_MIN_UP_DOWN_COUNT = 70;
static const l_float32 DEFAULT_MIN_UP_DOWN_CONF = 7.0;
static const l_float32 DEFAULT_MIN_UP_DOWN_RATIO = 2.5;
/* Parameters for determining mirror flip */
static const l_int32 DEFAULT_MIN_MIRROR_FLIP_COUNT = 100;
static const l_float32 DEFAULT_MIN_MIRROR_FLIP_CONF = 5.0;
/* Static debug function */
static void pixDebugFlipDetect(const char *filename, PIX *pixs,
PIX *pixhm, l_int32 enable);
/*----------------------------------------------------------------*
* Orientation detection (four 90 degree angles) *
* Rasterop implementation *
*----------------------------------------------------------------*/
/*!
* pixOrientDetect()
*
* Input: pixs (1 bpp, deskewed, English text, 150 - 300 ppi)
* &upconf (<optional return> ; may be null)
* &leftconf (<optional return> ; may be null)
* mincount (min number of up + down; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) See "Measuring document image skew and orientation"
* Dan S. Bloomberg, Gary E. Kopec and Lakshmi Dasari
* IS&T/SPIE EI'95, Conference 2422: Document Recognition II
* pp 302-316, Feb 6-7, 1995, San Jose, CA
* (2) upconf is the normalized difference between up ascenders
* and down ascenders. The image is analyzed without rotation
* for being rightside-up or upside-down. Set &upconf to null
* to skip this operation.
* (3) leftconf is the normalized difference between up ascenders
* and down ascenders in the image after it has been
* rotated 90 degrees clockwise. With that rotation, ascenders
* projecting to the left in the source image will project up
* in the rotated image. We compute this by rotating 90 degrees
* clockwise and testing for up and down ascenders. Set
* &leftconf to null to skip this operation.
* (4) Note that upconf and leftconf are not linear measures of
* confidence, e.g., in a range between 0 and 100. They
* measure how far you are out on the tail of a (presumably)
* normal distribution. For example, a confidence of 10 means
* that it is nearly certain that the difference did not
* happen at random. However, these values must be interpreted
* cautiously, taking into consideration the estimated prior
* for a particular orientation or mirror flip. The up-down
* signal is very strong if applied to text with ascenders
* up and down, and relatively weak for text at 90 degrees,
* but even at 90 degrees, the difference can look significant.
* For example, suppose the ascenders are oriented horizontally,
* but the test is done vertically. Then upconf can
* be < -MIN_CONF_FOR_UP_DOWN, suggesting the text may be
* upside-down. However, if instead the test were done
* horizontally, leftconf will be very much larger
* (in absolute value), giving the correct orientation.
* (5) If you compute both upconf and leftconf, and there is
* sufficient signal, the following table determines the
* cw angle necessary to rotate pixs so that the text is
* rightside-up:
* 0 deg : upconf >> 1, abs(upconf) >> abs(leftconf)
* 90 deg : leftconf >> 1, abs(leftconf) >> abs(upconf)
* 180 deg : upconf << -1, abs(upconf) >> abs(leftconf)
* 270 deg : leftconf << -1, abs(leftconf) >> abs(upconf)
* (6) One should probably not interpret the direction unless
* there are a sufficient number of counts for both orientations,
* in which case neither upconf nor leftconf will be 0.0.
* (7) Uses rasterop implementation of HMT.
*/
l_int32
pixOrientDetect(PIX *pixs,
l_float32 *pupconf,
l_float32 *pleftconf,
l_int32 mincount,
l_int32 debug)
{
PIX *pixt;
PROCNAME("pixOrientDetect");
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (pixGetDepth(pixs) != 1)
return ERROR_INT("pixs not 1 bpp", procName, 1);
if (!pupconf && !pleftconf)
return ERROR_INT("nothing to do", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_UP_DOWN_COUNT;
if (pupconf)
pixUpDownDetect(pixs, pupconf, mincount, debug);
if (pleftconf) {
pixt = pixRotate90(pixs, 1);
pixUpDownDetect(pixt, pleftconf, mincount, debug);
pixDestroy(&pixt);
}
return 0;
}
/*!
* makeOrientDecision()
*
* Input: upconf (nonzero)
* leftconf (nonzero)
* minupconf (minimum value for which a decision can be made)
* minratio (minimum conf ratio required for a decision)
* &orient (<return> text orientation enum {0,1,2,3,4})
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) This can be run after pixOrientDetect()
* (2) Both upconf and leftconf must be nonzero; otherwise the
* orientation cannot be determined.
* (3) The abs values of the input confidences are compared to
* minupconf.
* (4) The abs value of the largest of (upconf/leftconf) and
* (leftconf/upconf) is compared with minratio.
* (5) Input 0.0 for the default values for minupconf and minratio.
* (6) The return value of orient is interpreted thus:
* L_TEXT_ORIENT_UNKNOWN: not enough evidence to determine
* L_TEXT_ORIENT_UP: text rightside-up
* L_TEXT_ORIENT_LEFT: landscape, text up facing left
* L_TEXT_ORIENT_DOWN: text upside-down
* L_TEXT_ORIENT_RIGHT: landscape, text up facing right
*/
l_int32
makeOrientDecision(l_float32 upconf,
l_float32 leftconf,
l_float32 minupconf,
l_float32 minratio,
l_int32 *porient,
l_int32 debug)
{
l_float32 absupconf, absleftconf;
PROCNAME("makeOrientDecision");
if (!porient)
return ERROR_INT("&orient not defined", procName, 1);
*porient = L_TEXT_ORIENT_UNKNOWN; /* default: no decision */
if (upconf == 0.0 || leftconf == 0.0)
return ERROR_INT("not enough conf to get orientation", procName, 1);
if (minupconf == 0.0)
minupconf = DEFAULT_MIN_UP_DOWN_CONF;
if (minratio == 0.0)
minratio = DEFAULT_MIN_UP_DOWN_RATIO;
absupconf = L_ABS(upconf);
absleftconf = L_ABS(leftconf);
/* Here are the four possible orientation decisions, based
* on satisfaction of two threshold constraints. */
if (upconf > minupconf && absupconf > minratio * absleftconf)
*porient = L_TEXT_ORIENT_UP;
else if (leftconf > minupconf && absleftconf > minratio * absupconf)
*porient = L_TEXT_ORIENT_LEFT;
else if (upconf < -minupconf && absupconf > minratio * absleftconf)
*porient = L_TEXT_ORIENT_DOWN;
else if (leftconf < -minupconf && absleftconf > minratio * absupconf)
*porient = L_TEXT_ORIENT_RIGHT;
if (debug) {
fprintf(stderr, "upconf = %7.3f, leftconf = %7.3f\n", upconf, leftconf);
if (*porient == L_TEXT_ORIENT_UNKNOWN)
fprintf(stderr, "Confidence is low; no determination is made\n");
else if (*porient == L_TEXT_ORIENT_UP)
fprintf(stderr, "Text is rightside-up\n");
else if (*porient == L_TEXT_ORIENT_LEFT)
fprintf(stderr, "Text is rotated 90 deg ccw\n");
else if (*porient == L_TEXT_ORIENT_DOWN)
fprintf(stderr, "Text is upside-down\n");
else /* *porient == L_TEXT_ORIENT_RIGHT */
fprintf(stderr, "Text is rotated 90 deg cw\n");
}
return 0;
}
/*!
* pixUpDownDetect()
*
* Input: pixs (1 bpp, deskewed, English text, 150 - 300 ppi)
* &conf (<return> confidence that text is rightside-up)
* mincount (min number of up + down; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) Special (typical, slightly faster) case, where the pixels
* identified through the HMT (hit-miss transform) are not
* clipped by a truncated word mask pixm. See pixOrientDetect()
* and pixUpDownDetectGeneral() for details.
* (2) The returned confidence is the normalized difference
* between the number of detected up and down ascenders,
* assuming that the text is either rightside-up or upside-down
* and not rotated at a 90 degree angle.
*/
l_int32
pixUpDownDetect(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 debug)
{
return pixUpDownDetectGeneral(pixs, pconf, mincount, 0, debug);
}
/*!
* pixUpDownDetectGeneral()
*
* Input: pixs (1 bpp, deskewed, English text, 150 - 300 ppi)
* &conf (<return> confidence that text is rightside-up)
* mincount (min number of up + down; use 0 for default)
* npixels (number of pixels removed from each side of word box)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) See pixOrientDetect() for other details.
* (2) @conf is the normalized difference between the number of
* detected up and down ascenders, assuming that the text
* is either rightside-up or upside-down and not rotated
* at a 90 degree angle.
* (3) The typical mode of operation is @npixels == 0.
* If @npixels > 0, this removes HMT matches at the
* beginning and ending of "words." This is useful for
* pages that may have mostly digits, because if npixels == 0,
* leading "1" and "3" digits can register as having
* ascenders or descenders, and "7" digits can match descenders.
* Consequently, a page image of only digits may register
* as being upside-down.
* (4) We want to count the number of instances found using the HMT.
* An expensive way to do this would be to count the
* number of connected components. A cheap way is to do a rank
* reduction cascade that reduces each component to a single
* pixel, and results (after two or three 2x reductions)
* in one pixel for each of the original components.
* After the reduction, you have a much smaller pix over
* which to count pixels. We do only 2 reductions, because
* this function is designed to work for input pix between
* 150 and 300 ppi, and an 8x reduction on a 150 ppi image
* is going too far -- components will get merged.
*/
l_int32
pixUpDownDetectGeneral(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 npixels,
l_int32 debug)
{
l_int32 countup, countdown, nmax;
l_float32 nup, ndown;
PIX *pixt0, *pixt1, *pixt2, *pixt3, *pixm;
SEL *sel1, *sel2, *sel3, *sel4;
PROCNAME("pixUpDownDetectGeneral");
if (!pconf)
return ERROR_INT("&conf not defined", procName, 1);
*pconf = 0.0;
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_UP_DOWN_COUNT;
if (npixels < 0)
npixels = 0;
sel1 = selCreateFromString(textsel1, 5, 6, NULL);
sel2 = selCreateFromString(textsel2, 5, 6, NULL);
sel3 = selCreateFromString(textsel3, 5, 6, NULL);
sel4 = selCreateFromString(textsel4, 5, 6, NULL);
/* One of many reasonable pre-filtering sequences: (1, 8) and (30, 1).
* This closes holes in x-height characters and joins them at
* the x-height. There is more noise in the descender detection
* from this, but it works fairly well. */
pixt0 = pixMorphCompSequence(pixs, "c1.8 + c30.1", 0);
/* Optionally, make a mask of the word bounding boxes, shortening
* each of them by a fixed amount at each end. */
pixm = NULL;
if (npixels > 0) {
l_int32 i, nbox, x, y, w, h;
BOX *box;
BOXA *boxa;
pixt1 = pixMorphSequence(pixt0, "o10.1", 0);
boxa = pixConnComp(pixt1, NULL, 8);
pixm = pixCreateTemplate(pixt1);
pixDestroy(&pixt1);
nbox = boxaGetCount(boxa);
for (i = 0; i < nbox; i++) {
box = boxaGetBox(boxa, i, L_CLONE);
boxGetGeometry(box, &x, &y, &w, &h);
if (w > 2 * npixels)
pixRasterop(pixm, x + npixels, y - 6, w - 2 * npixels, h + 13,
PIX_SET, NULL, 0, 0);
boxDestroy(&box);
}
boxaDestroy(&boxa);
}
/* Find the ascenders and optionally filter with pixm.
* For an explanation of the procedure used for counting the result
* of the HMT, see comments at the beginning of this function. */
pixt1 = pixHMT(NULL, pixt0, sel1);
pixt2 = pixHMT(NULL, pixt0, sel2);
pixOr(pixt1, pixt1, pixt2);
if (pixm)
pixAnd(pixt1, pixt1, pixm);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &countup, NULL);
pixDebugFlipDetect("junkpixup", pixs, pixt1, debug);
pixDestroy(&pixt1);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
/* Find the ascenders and optionally filter with pixm. */
pixt1 = pixHMT(NULL, pixt0, sel3);
pixt2 = pixHMT(NULL, pixt0, sel4);
pixOr(pixt1, pixt1, pixt2);
if (pixm)
pixAnd(pixt1, pixt1, pixm);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &countdown, NULL);
pixDebugFlipDetect("junkpixdown", pixs, pixt1, debug);
pixDestroy(&pixt1);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
/* Evaluate statistically, generating a confidence that is
* related to the probability with a gaussian distribution. */
nup = (l_float32)(countup);
ndown = (l_float32)(countdown);
nmax = L_MAX(countup, countdown);
if (nmax > mincount)
*pconf = 2. * ((nup - ndown) / sqrt(nup + ndown));
if (debug) {
if (pixm) pixWrite("junkpixm1", pixm, IFF_PNG);
fprintf(stderr, "nup = %7.3f, ndown = %7.3f, conf = %7.3f\n",
nup, ndown, *pconf);
if (*pconf > DEFAULT_MIN_UP_DOWN_CONF)
fprintf(stderr, "Text is rightside-up\n");
if (*pconf < -DEFAULT_MIN_UP_DOWN_CONF)
fprintf(stderr, "Text is upside-down\n");
}
pixDestroy(&pixt0);
pixDestroy(&pixm);
selDestroy(&sel1);
selDestroy(&sel2);
selDestroy(&sel3);
selDestroy(&sel4);
return 0;
}
/*----------------------------------------------------------------*
* Orientation detection (four 90 degree angles) *
* DWA implementation *
*----------------------------------------------------------------*/
/*!
* pixOrientDetectDwa()
*
* Input: pixs (1 bpp, deskewed, English text)
* &upconf (<optional return> ; may be null)
* &leftconf (<optional return> ; may be null)
* mincount (min number of up + down; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) Same interface as for pixOrientDetect(). See notes
* there for usage.
* (2) Uses auto-gen'd code for the Sels defined at the
* top of this file, with some renaming of functions.
* The auto-gen'd code is in fliphmtgen.c, and can
* be generated by a simple executable; see prog/flipselgen.c.
* (3) This runs about 2.5 times faster than the pixOrientDetect().
*/
l_int32
pixOrientDetectDwa(PIX *pixs,
l_float32 *pupconf,
l_float32 *pleftconf,
l_int32 mincount,
l_int32 debug)
{
PIX *pixt;
PROCNAME("pixOrientDetectDwa");
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (pixGetDepth(pixs) != 1)
return ERROR_INT("pixs not 1 bpp", procName, 1);
if (!pupconf && !pleftconf)
return ERROR_INT("nothing to do", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_UP_DOWN_COUNT;
if (pupconf)
pixUpDownDetectDwa(pixs, pupconf, mincount, debug);
if (pleftconf) {
pixt = pixRotate90(pixs, 1);
pixUpDownDetectDwa(pixt, pleftconf, mincount, debug);
pixDestroy(&pixt);
}
return 0;
}
/*!
* pixUpDownDetectDwa()
*
* Input: pixs (1 bpp, deskewed, English text, 150 - 300 ppi)
* &conf (<return> confidence that text is rightside-up)
* mincount (min number of up + down; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) Faster (DWA) version of pixUpDownDetect().
* (2) This is a special case (but typical and slightly faster) of
* pixUpDownDetectGeneralDwa(), where the pixels identified
* through the HMT (hit-miss transform) are not clipped by
* a truncated word mask pixm. See pixUpDownDetectGeneral()
* for usage and other details.
* (3) The returned confidence is the normalized difference
* between the number of detected up and down ascenders,
* assuming that the text is either rightside-up or upside-down
* and not rotated at a 90 degree angle.
*/
l_int32
pixUpDownDetectDwa(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 debug)
{
return pixUpDownDetectGeneralDwa(pixs, pconf, mincount, 0, debug);
}
/*!
* pixUpDownDetectGeneralDwa()
*
* Input: pixs (1 bpp, deskewed, English text)
* &conf (<return> confidence that text is rightside-up)
* mincount (min number of up + down; use 0 for default)
* npixels (number of pixels removed from each side of word box)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) See the notes in pixUpDownDetectGeneral() for usage.
*/
l_int32
pixUpDownDetectGeneralDwa(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 npixels,
l_int32 debug)
{
char flipsel1[] = "flipsel1";
char flipsel2[] = "flipsel2";
char flipsel3[] = "flipsel3";
char flipsel4[] = "flipsel4";
l_int32 countup, countdown, nmax;
l_float32 nup, ndown;
PIX *pixt, *pixt0, *pixt1, *pixt2, *pixt3, *pixm;
PROCNAME("pixUpDownDetectGeneralDwa");
if (!pconf)
return ERROR_INT("&conf not defined", procName, 1);
*pconf = 0.0;
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_UP_DOWN_COUNT;
if (npixels < 0)
npixels = 0;
/* One of many reasonable pre-filtering sequences: (1, 8) and (30, 1).
* This closes holes in x-height characters and joins them at
* the x-height. There is more noise in the descender detection
* from this, but it works fairly well. */
pixt = pixMorphSequenceDwa(pixs, "c1.8 + c30.1", 0);
/* Be sure to add the border before the flip DWA operations! */
pixt0 = pixAddBorderGeneral(pixt, ADDED_BORDER, ADDED_BORDER,
ADDED_BORDER, ADDED_BORDER, 0);
pixDestroy(&pixt);
/* Optionally, make a mask of the word bounding boxes, shortening
* each of them by a fixed amount at each end. */
pixm = NULL;
if (npixels > 0) {
l_int32 i, nbox, x, y, w, h;
BOX *box;
BOXA *boxa;
pixt1 = pixMorphSequenceDwa(pixt0, "o10.1", 0);
boxa = pixConnComp(pixt1, NULL, 8);
pixm = pixCreateTemplate(pixt1);
pixDestroy(&pixt1);
nbox = boxaGetCount(boxa);
for (i = 0; i < nbox; i++) {
box = boxaGetBox(boxa, i, L_CLONE);
boxGetGeometry(box, &x, &y, &w, &h);
if (w > 2 * npixels)
pixRasterop(pixm, x + npixels, y - 6, w - 2 * npixels, h + 13,
PIX_SET, NULL, 0, 0);
boxDestroy(&box);
}
boxaDestroy(&boxa);
}
/* Find the ascenders and optionally filter with pixm.
* For an explanation of the procedure used for counting the result
* of the HMT, see comments in pixUpDownDetectGeneral(). */
pixt1 = pixFlipFHMTGen(NULL, pixt0, flipsel1);
pixt2 = pixFlipFHMTGen(NULL, pixt0, flipsel2);
pixOr(pixt1, pixt1, pixt2);
if (pixm)
pixAnd(pixt1, pixt1, pixm);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &countup, NULL);
pixDestroy(&pixt1);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
/* Find the ascenders and optionally filter with pixm. */
pixt1 = pixFlipFHMTGen(NULL, pixt0, flipsel3);
pixt2 = pixFlipFHMTGen(NULL, pixt0, flipsel4);
pixOr(pixt1, pixt1, pixt2);
if (pixm)
pixAnd(pixt1, pixt1, pixm);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &countdown, NULL);
pixDestroy(&pixt1);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
/* Evaluate statistically, generating a confidence that is
* related to the probability with a gaussian distribution. */
nup = (l_float32)(countup);
ndown = (l_float32)(countdown);
nmax = L_MAX(countup, countdown);
if (nmax > mincount)
*pconf = 2. * ((nup - ndown) / sqrt(nup + ndown));
if (debug) {
if (pixm) pixWrite("junkpixm2", pixm, IFF_PNG);
fprintf(stderr, "nup = %7.3f, ndown = %7.3f, conf = %7.3f\n",
nup, ndown, *pconf);
if (*pconf > DEFAULT_MIN_UP_DOWN_CONF)
fprintf(stderr, "Text is rightside-up\n");
if (*pconf < -DEFAULT_MIN_UP_DOWN_CONF)
fprintf(stderr, "Text is upside-down\n");
}
pixDestroy(&pixt0);
pixDestroy(&pixm);
return 0;
}
/*----------------------------------------------------------------*
* Left-right mirror detection *
* Rasterop implementation *
*----------------------------------------------------------------*/
/*!
* pixMirrorDetect()
*
* Input: pixs (1 bpp, deskewed, English text)
* &conf (<return> confidence that text is not LR mirror reversed)
* mincount (min number of left + right; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) For this test, it is necessary that the text is horizontally
* oriented, with ascenders going up.
* (2) conf is the normalized difference between the number of
* right and left facing characters with ascenders.
* Left-facing are {d}; right-facing are {b, h, k}.
* At least that was the expectation. In practice, we can
* really just say that it is the normalized difference in
* hits using two specific hit-miss filters, textsel1 and textsel2,
* after the image has been suitably pre-filtered so that
* these filters are effective. See (4) for what's really happening.
* (3) A large positive conf value indicates normal text, whereas
* a large negative conf value means the page is mirror reversed.
* (4) The implementation is a bit tricky. The general idea is
* to fill the x-height part of characters, but not the space
* between them, before doing the HMT. This is done by
* finding pixels added using two different operations -- a
* horizontal close and a vertical dilation -- and adding
* the intersection of these sets to the original. It turns
* out that the original intuition about the signal was largely
* in error: much of the signal for right-facing characters
* comes from the lower part of common x-height characters, like
* the e and c, that remain open after these operations.
* So it's important that the operations to close the x-height
* parts of the characters are purposely weakened sufficiently
* to allow these characters to remain open. The wonders
* of morphology!
*/
l_int32
pixMirrorDetect(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 debug)
{
l_int32 count1, count2, nmax;
l_float32 nleft, nright;
PIX *pixt0, *pixt1, *pixt2, *pixt3;
SEL *sel1, *sel2;
PROCNAME("pixMirrorDetect");
if (!pconf)
return ERROR_INT("&conf not defined", procName, 1);
*pconf = 0.0;
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_MIRROR_FLIP_COUNT;
sel1 = selCreateFromString(textsel1, 5, 6, NULL);
sel2 = selCreateFromString(textsel2, 5, 6, NULL);
/* Fill x-height characters but not space between them, sort of. */
pixt3 = pixMorphCompSequence(pixs, "d1.30", 0);
pixXor(pixt3, pixt3, pixs);
pixt0 = pixMorphCompSequence(pixs, "c15.1", 0);
pixXor(pixt0, pixt0, pixs);
pixAnd(pixt0, pixt0, pixt3);
pixOr(pixt0, pixt0, pixs);
pixDestroy(&pixt3);
/* pixDisplayWrite(pixt0, 1); */
/* Filter the right-facing characters. */
pixt1 = pixHMT(NULL, pixt0, sel1);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &count1, NULL);
pixDebugFlipDetect("junkpixright", pixs, pixt1, debug);
pixDestroy(&pixt1);
pixDestroy(&pixt3);
/* Filter the left-facing characters. */
pixt2 = pixHMT(NULL, pixt0, sel2);
pixt3 = pixReduceRankBinaryCascade(pixt2, 1, 1, 0, 0);
pixCountPixels(pixt3, &count2, NULL);
pixDebugFlipDetect("junkpixleft", pixs, pixt2, debug);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
nright = (l_float32)count1;
nleft = (l_float32)count2;
nmax = L_MAX(count1, count2);
pixDestroy(&pixt0);
selDestroy(&sel1);
selDestroy(&sel2);
if (nmax > mincount)
*pconf = 2. * ((nright - nleft) / sqrt(nright + nleft));
if (debug) {
fprintf(stderr, "nright = %f, nleft = %f\n", nright, nleft);
if (*pconf > DEFAULT_MIN_MIRROR_FLIP_CONF)
fprintf(stderr, "Text is not mirror reversed\n");
if (*pconf < -DEFAULT_MIN_MIRROR_FLIP_CONF)
fprintf(stderr, "Text is mirror reversed\n");
}
return 0;
}
/*----------------------------------------------------------------*
* Left-right mirror detection *
* DWA implementation *
*----------------------------------------------------------------*/
/*!
* pixMirrorDetectDwa()
*
* Input: pixs (1 bpp, deskewed, English text)
* &conf (<return> confidence that text is not LR mirror reversed)
* mincount (min number of left + right; use 0 for default)
* debug (1 for debug output; 0 otherwise)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) We assume the text is horizontally oriented, with
* ascenders going up.
* (2) See notes in pixMirrorDetect().
*/
l_int32
pixMirrorDetectDwa(PIX *pixs,
l_float32 *pconf,
l_int32 mincount,
l_int32 debug)
{
char flipsel1[] = "flipsel1";
char flipsel2[] = "flipsel2";
l_int32 count1, count2, nmax;
l_float32 nleft, nright;
PIX *pixt0, *pixt1, *pixt2, *pixt3;
PROCNAME("pixMirrorDetectDwa");
if (!pconf)
return ERROR_INT("&conf not defined", procName, 1);
*pconf = 0.0;
if (!pixs)
return ERROR_INT("pixs not defined", procName, 1);
if (mincount == 0)
mincount = DEFAULT_MIN_MIRROR_FLIP_COUNT;
/* Fill x-height characters but not space between them, sort of. */
pixt3 = pixMorphSequenceDwa(pixs, "d1.30", 0);
pixXor(pixt3, pixt3, pixs);
pixt0 = pixMorphSequenceDwa(pixs, "c15.1", 0);
pixXor(pixt0, pixt0, pixs);
pixAnd(pixt0, pixt0, pixt3);
pixOr(pixt3, pixt0, pixs);
pixDestroy(&pixt0);
pixt0 = pixAddBorderGeneral(pixt3, ADDED_BORDER, ADDED_BORDER,
ADDED_BORDER, ADDED_BORDER, 0);
pixDestroy(&pixt3);
/* Filter the right-facing characters. */
pixt1 = pixFlipFHMTGen(NULL, pixt0, flipsel1);
pixt3 = pixReduceRankBinaryCascade(pixt1, 1, 1, 0, 0);
pixCountPixels(pixt3, &count1, NULL);
pixDestroy(&pixt1);
pixDestroy(&pixt3);
/* Filter the left-facing characters. */
pixt2 = pixFlipFHMTGen(NULL, pixt0, flipsel2);
pixt3 = pixReduceRankBinaryCascade(pixt2, 1, 1, 0, 0);
pixCountPixels(pixt3, &count2, NULL);
pixDestroy(&pixt2);
pixDestroy(&pixt3);
pixDestroy(&pixt0);
nright = (l_float32)count1;
nleft = (l_float32)count2;
nmax = L_MAX(count1, count2);
if (nmax > mincount)
*pconf = 2. * ((nright - nleft) / sqrt(nright + nleft));
if (debug) {
fprintf(stderr, "nright = %f, nleft = %f\n", nright, nleft);
if (*pconf > DEFAULT_MIN_MIRROR_FLIP_CONF)
fprintf(stderr, "Text is not mirror reversed\n");
if (*pconf < -DEFAULT_MIN_MIRROR_FLIP_CONF)
fprintf(stderr, "Text is mirror reversed\n");
}
return 0;
}
/*----------------------------------------------------------------*
* Static debug helper *
*----------------------------------------------------------------*/
/*
* pixDebugFlipDetect()
*
* Input: filename (for output debug file)
* pixs (input to pix*Detect)
* pixhm (hit-miss result from ascenders or descenders)
* enable (1 to enable this function; 0 to disable)
* Return: void
*/
static void
pixDebugFlipDetect(const char *filename,
PIX *pixs,
PIX *pixhm,
l_int32 enable)
{
PIX *pixt, *pixthm;
if (!enable) return;
/* Display with red dot at counted locations */
pixt = pixConvert1To4Cmap(pixs);
pixthm = pixMorphSequence(pixhm, "d5.5", 0);
pixSetMaskedCmap(pixt, pixthm, 0, 0, 255, 0, 0);
pixWrite(filename, pixt, IFF_PNG);
pixDestroy(&pixthm);
pixDestroy(&pixt);
return;
}