tesseract  5.0.0-alpha-619-ge9db
fixxht.cpp
Go to the documentation of this file.
1 /**********************************************************************
2  * File: fixxht.cpp (Formerly fixxht.c)
3  * Description: Improve x_ht and look out for case inconsistencies
4  * Author: Phil Cheatle
5  * Created: Thu Aug 5 14:11:08 BST 1993
6  *
7  * (C) Copyright 1992, Hewlett-Packard Ltd.
8  ** Licensed under the Apache License, Version 2.0 (the "License");
9  ** you may not use this file except in compliance with the License.
10  ** You may obtain a copy of the License at
11  ** http://www.apache.org/licenses/LICENSE-2.0
12  ** Unless required by applicable law or agreed to in writing, software
13  ** distributed under the License is distributed on an "AS IS" BASIS,
14  ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  ** See the License for the specific language governing permissions and
16  ** limitations under the License.
17  *
18  **********************************************************************/
19 
20 #include <algorithm>
21 #include <cstring>
22 #include <cctype>
23 #include "params.h"
24 #include "float2int.h"
25 #include "tesseractclass.h"
26 
27 namespace tesseract {
28 
29 // Fixxht overview.
30 // Premise: Initial estimate of x-height is adequate most of the time, but
31 // occasionally it is incorrect. Most notable causes of failure are:
32 // 1. Small caps, where the top of the caps is the same as the body text
33 // xheight. For small caps words the xheight needs to be reduced to correctly
34 // recognize the caps in the small caps word.
35 // 2. All xheight lines, such as summer. Here the initial estimate will have
36 // guessed that the blob tops are caps and will have placed the xheight too low.
37 // 3. Noise/logos beside words, or changes in font size on a line. Such
38 // things can blow the statistics and cause an incorrect estimate.
39 // 4. Incorrect baseline. Can happen when 2 columns are incorrectly merged.
40 // In this case the x-height is often still correct.
41 //
42 // Algorithm.
43 // Compare the vertical position (top only) of alphnumerics in a word with
44 // the range of positions in training data (in the unicharset).
45 // See CountMisfitTops. If any characters disagree sufficiently with the
46 // initial xheight estimate, then recalculate the xheight, re-run OCR on
47 // the word, and if the number of vertical misfits goes down, along with
48 // either the word rating or certainty, then keep the new xheight.
49 // The new xheight is calculated as follows:ComputeCompatibleXHeight
50 // For each alphanumeric character that has a vertically misplaced top
51 // (a misfit), yet its bottom is within the acceptable range (ie it is not
52 // likely a sub-or super-script) calculate the range of acceptable xheight
53 // positions from its range of tops, and give each value in the range a
54 // number of votes equal to the distance of its top from its acceptance range.
55 // The x-height position with the median of the votes becomes the new
56 // x-height. This assumes that most characters will be correctly recognized
57 // even if the x-height is incorrect. This is not a terrible assumption, but
58 // it is not great. An improvement would be to use a classifier that does
59 // not care about vertical position or scaling at all.
60 // Separately collect stats on shifted baselines and apply the same logic to
61 // computing a best-fit shift to fix the error. If the baseline needs to be
62 // shifted, but the x-height is OK, returns the original x-height along with
63 // the baseline shift to indicate that recognition needs to re-run.
64 
65 // If the max-min top of a unicharset char is bigger than kMaxCharTopRange
66 // then the char top cannot be used to judge misfits or suggest a new top.
67 const int kMaxCharTopRange = 48;
68 
69 // Returns the number of misfit blob tops in this word.
70 int Tesseract::CountMisfitTops(WERD_RES *word_res) {
71  int bad_blobs = 0;
72  int num_blobs = word_res->rebuild_word->NumBlobs();
73  for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
74  TBLOB* blob = word_res->rebuild_word->blobs[blob_id];
75  UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
76  if (unicharset.get_isalpha(class_id) || unicharset.get_isdigit(class_id)) {
77  int top = blob->bounding_box().top();
78  if (top >= INT_FEAT_RANGE)
79  top = INT_FEAT_RANGE - 1;
80  int min_bottom, max_bottom, min_top, max_top;
81  unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom,
82  &min_top, &max_top);
83  if (max_top - min_top > kMaxCharTopRange)
84  continue;
85  bool bad = top < min_top - x_ht_acceptance_tolerance ||
86  top > max_top + x_ht_acceptance_tolerance;
87  if (bad)
88  ++bad_blobs;
89  if (debug_x_ht_level >= 1) {
90  tprintf("Class %s is %s with top %d vs limits of %d->%d, +/-%d\n",
91  unicharset.id_to_unichar(class_id),
92  bad ? "Misfit" : "OK", top, min_top, max_top,
93  static_cast<int>(x_ht_acceptance_tolerance));
94  }
95  }
96  }
97  return bad_blobs;
98 }
99 
100 // Returns a new x-height maximally compatible with the result in word_res.
101 // See comment above for overall algorithm.
103  float* baseline_shift) {
104  STATS top_stats(0, UINT8_MAX);
105  STATS shift_stats(-UINT8_MAX, UINT8_MAX);
106  int bottom_shift = 0;
107  int num_blobs = word_res->rebuild_word->NumBlobs();
108  do {
109  top_stats.clear();
110  shift_stats.clear();
111  for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
112  TBLOB* blob = word_res->rebuild_word->blobs[blob_id];
113  UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
114  if (unicharset.get_isalpha(class_id) ||
115  unicharset.get_isdigit(class_id)) {
116  int top = blob->bounding_box().top() + bottom_shift;
117  // Clip the top to the limit of normalized feature space.
118  if (top >= INT_FEAT_RANGE)
119  top = INT_FEAT_RANGE - 1;
120  int bottom = blob->bounding_box().bottom() + bottom_shift;
121  int min_bottom, max_bottom, min_top, max_top;
122  unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom,
123  &min_top, &max_top);
124  // Chars with a wild top range would mess up the result so ignore them.
125  if (max_top - min_top > kMaxCharTopRange)
126  continue;
127  int misfit_dist = std::max((min_top - x_ht_acceptance_tolerance) - top,
128  top - (max_top + x_ht_acceptance_tolerance));
129  int height = top - kBlnBaselineOffset;
130  if (debug_x_ht_level >= 2) {
131  tprintf("Class %s: height=%d, bottom=%d,%d top=%d,%d, actual=%d,%d: ",
132  unicharset.id_to_unichar(class_id),
133  height, min_bottom, max_bottom, min_top, max_top,
134  bottom, top);
135  }
136  // Use only chars that fit in the expected bottom range, and where
137  // the range of tops is sensibly near the xheight.
138  if (min_bottom <= bottom + x_ht_acceptance_tolerance &&
139  bottom - x_ht_acceptance_tolerance <= max_bottom &&
140  min_top > kBlnBaselineOffset &&
141  max_top - kBlnBaselineOffset >= kBlnXHeight &&
142  misfit_dist > 0) {
143  // Compute the x-height position using proportionality between the
144  // actual height and expected height.
145  int min_xht = DivRounded(height * kBlnXHeight,
146  max_top - kBlnBaselineOffset);
147  int max_xht = DivRounded(height * kBlnXHeight,
148  min_top - kBlnBaselineOffset);
149  if (debug_x_ht_level >= 2) {
150  tprintf(" xht range min=%d, max=%d\n", min_xht, max_xht);
151  }
152  // The range of expected heights gets a vote equal to the distance
153  // of the actual top from the expected top.
154  for (int y = min_xht; y <= max_xht; ++y)
155  top_stats.add(y, misfit_dist);
156  } else if ((min_bottom > bottom + x_ht_acceptance_tolerance ||
157  bottom - x_ht_acceptance_tolerance > max_bottom) &&
158  bottom_shift == 0) {
159  // Get the range of required bottom shift.
160  int min_shift = min_bottom - bottom;
161  int max_shift = max_bottom - bottom;
162  if (debug_x_ht_level >= 2) {
163  tprintf(" bottom shift min=%d, max=%d\n", min_shift, max_shift);
164  }
165  // The range of expected shifts gets a vote equal to the min distance
166  // of the actual bottom from the expected bottom, spread over the
167  // range of its acceptance.
168  int misfit_weight = abs(min_shift);
169  if (max_shift > min_shift)
170  misfit_weight /= max_shift - min_shift;
171  for (int y = min_shift; y <= max_shift; ++y)
172  shift_stats.add(y, misfit_weight);
173  } else {
174  if (bottom_shift == 0) {
175  // Things with bottoms that are already ok need to say so, on the
176  // 1st iteration only.
177  shift_stats.add(0, kBlnBaselineOffset);
178  }
179  if (debug_x_ht_level >= 2) {
180  tprintf(" already OK\n");
181  }
182  }
183  }
184  }
185  if (shift_stats.get_total() > top_stats.get_total()) {
186  bottom_shift = IntCastRounded(shift_stats.median());
187  if (debug_x_ht_level >= 2) {
188  tprintf("Applying bottom shift=%d\n", bottom_shift);
189  }
190  }
191  } while (bottom_shift != 0 &&
192  top_stats.get_total() < shift_stats.get_total());
193  // Baseline shift is opposite sign to the bottom shift.
194  *baseline_shift = -bottom_shift / word_res->denorm.y_scale();
195  if (debug_x_ht_level >= 2) {
196  tprintf("baseline shift=%g\n", *baseline_shift);
197  }
198  if (top_stats.get_total() == 0)
199  return bottom_shift != 0 ? word_res->x_height : 0.0f;
200  // The new xheight is just the median vote, which is then scaled out
201  // of BLN space back to pixel space to get the x-height in pixel space.
202  float new_xht = top_stats.median();
203  if (debug_x_ht_level >= 2) {
204  tprintf("Median xht=%f\n", new_xht);
205  tprintf("Mode20:A: New x-height = %f (norm), %f (orig)\n",
206  new_xht, new_xht / word_res->denorm.y_scale());
207  }
208  // The xheight must change by at least x_ht_min_change to be used.
209  if (fabs(new_xht - kBlnXHeight) >= x_ht_min_change)
210  return new_xht / word_res->denorm.y_scale();
211  else
212  return bottom_shift != 0 ? word_res->x_height : 0.0f;
213 }
214 
215 } // namespace tesseract
kBlnXHeight
const int kBlnXHeight
Definition: normalis.h:23
tesseract::kMaxCharTopRange
const int kMaxCharTopRange
Definition: fixxht.cpp:82
tesseract::Tesseract::x_ht_acceptance_tolerance
int x_ht_acceptance_tolerance
Definition: tesseractclass.h:970
tesseract::Tesseract::ComputeCompatibleXheight
float ComputeCompatibleXheight(WERD_RES *word_res, float *baseline_shift)
Definition: fixxht.cpp:117
WERD_CHOICE::unichar_id
UNICHAR_ID unichar_id(int index) const
Definition: ratngs.h:303
UNICHARSET::get_isdigit
bool get_isdigit(UNICHAR_ID unichar_id) const
Definition: unicharset.h:502
WERD_RES::rebuild_word
TWERD * rebuild_word
Definition: pageres.h:260
UNICHARSET::get_isalpha
bool get_isalpha(UNICHAR_ID unichar_id) const
Definition: unicharset.h:481
tesseractclass.h
tesseract::Tesseract::CountMisfitTops
int CountMisfitTops(WERD_RES *word_res)
Definition: fixxht.cpp:85
WERD_RES::denorm
DENORM denorm
Definition: pageres.h:195
INT_FEAT_RANGE
#define INT_FEAT_RANGE
Definition: float2int.h:26
params.h
TBOX::top
int16_t top() const
Definition: rect.h:57
WERD_RES::x_height
float x_height
Definition: pageres.h:310
WERD_RES
Definition: pageres.h:160
IntCastRounded
int IntCastRounded(double x)
Definition: helpers.h:173
tesseract::CCUtil::unicharset
UNICHARSET unicharset
Definition: ccutil.h:57
tesseract::Tesseract::debug_x_ht_level
int debug_x_ht_level
Definition: tesseractclass.h:872
WERD_RES::best_choice
WERD_CHOICE * best_choice
Definition: pageres.h:235
UNICHARSET::get_top_bottom
void get_top_bottom(UNICHAR_ID unichar_id, int *min_bottom, int *max_bottom, int *min_top, int *max_top) const
Definition: unicharset.h:558
DENORM::y_scale
float y_scale() const
Definition: normalis.h:269
TWERD::blobs
GenericVector< TBLOB * > blobs
Definition: blobs.h:457
TBOX::bottom
int16_t bottom() const
Definition: rect.h:64
float2int.h
tesseract
Definition: baseapi.h:65
DivRounded
int DivRounded(int a, int b)
Definition: helpers.h:165
tesseract::Tesseract::x_ht_min_change
int x_ht_min_change
Definition: tesseractclass.h:971
STATS
Definition: statistc.h:30
UNICHAR_ID
int UNICHAR_ID
Definition: unichar.h:36
TBLOB::bounding_box
TBOX bounding_box() const
Definition: blobs.cpp:466
TBLOB
Definition: blobs.h:282
tprintf
DLLSYM void tprintf(const char *format,...)
Definition: tprintf.cpp:34
UNICHARSET::id_to_unichar
const char * id_to_unichar(UNICHAR_ID id) const
Definition: unicharset.cpp:290
kBlnBaselineOffset
const int kBlnBaselineOffset
Definition: normalis.h:24
TWERD::NumBlobs
int NumBlobs() const
Definition: blobs.h:446