tesseract  5.0.0
fixxht.cpp
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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 "float2int.h"
21 #include "params.h"
22 #include "tesseractclass.h"
23 
24 #include <algorithm>
25 #include <cctype>
26 #include <cmath>
27 #include <cstring>
28 
29 namespace tesseract {
30 
31 // Fixxht overview.
32 // Premise: Initial estimate of x-height is adequate most of the time, but
33 // occasionally it is incorrect. Most notable causes of failure are:
34 // 1. Small caps, where the top of the caps is the same as the body text
35 // xheight. For small caps words the xheight needs to be reduced to correctly
36 // recognize the caps in the small caps word.
37 // 2. All xheight lines, such as summer. Here the initial estimate will have
38 // guessed that the blob tops are caps and will have placed the xheight too low.
39 // 3. Noise/logos beside words, or changes in font size on a line. Such
40 // things can blow the statistics and cause an incorrect estimate.
41 // 4. Incorrect baseline. Can happen when 2 columns are incorrectly merged.
42 // In this case the x-height is often still correct.
43 //
44 // Algorithm.
45 // Compare the vertical position (top only) of alphnumerics in a word with
46 // the range of positions in training data (in the unicharset).
47 // See CountMisfitTops. If any characters disagree sufficiently with the
48 // initial xheight estimate, then recalculate the xheight, re-run OCR on
49 // the word, and if the number of vertical misfits goes down, along with
50 // either the word rating or certainty, then keep the new xheight.
51 // The new xheight is calculated as follows:ComputeCompatibleXHeight
52 // For each alphanumeric character that has a vertically misplaced top
53 // (a misfit), yet its bottom is within the acceptable range (ie it is not
54 // likely a sub-or super-script) calculate the range of acceptable xheight
55 // positions from its range of tops, and give each value in the range a
56 // number of votes equal to the distance of its top from its acceptance range.
57 // The x-height position with the median of the votes becomes the new
58 // x-height. This assumes that most characters will be correctly recognized
59 // even if the x-height is incorrect. This is not a terrible assumption, but
60 // it is not great. An improvement would be to use a classifier that does
61 // not care about vertical position or scaling at all.
62 // Separately collect stats on shifted baselines and apply the same logic to
63 // computing a best-fit shift to fix the error. If the baseline needs to be
64 // shifted, but the x-height is OK, returns the original x-height along with
65 // the baseline shift to indicate that recognition needs to re-run.
66 
67 // If the max-min top of a unicharset char is bigger than kMaxCharTopRange
68 // then the char top cannot be used to judge misfits or suggest a new top.
69 const int kMaxCharTopRange = 48;
70 
71 // Returns the number of misfit blob tops in this word.
73  int bad_blobs = 0;
74  int num_blobs = word_res->rebuild_word->NumBlobs();
75  for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
76  TBLOB *blob = word_res->rebuild_word->blobs[blob_id];
77  UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
78  if (unicharset.get_isalpha(class_id) || unicharset.get_isdigit(class_id)) {
79  int top = blob->bounding_box().top();
80  if (top >= INT_FEAT_RANGE) {
81  top = INT_FEAT_RANGE - 1;
82  }
83  int min_bottom, max_bottom, min_top, max_top;
84  unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom, &min_top, &max_top);
85  if (max_top - min_top > kMaxCharTopRange) {
86  continue;
87  }
88  bool bad =
89  top < min_top - x_ht_acceptance_tolerance || top > max_top + x_ht_acceptance_tolerance;
90  if (bad) {
91  ++bad_blobs;
92  }
93  if (debug_x_ht_level >= 1) {
94  tprintf("Class %s is %s with top %d vs limits of %d->%d, +/-%d\n",
95  unicharset.id_to_unichar(class_id), bad ? "Misfit" : "OK", top, min_top, max_top,
96  static_cast<int>(x_ht_acceptance_tolerance));
97  }
98  }
99  }
100  return bad_blobs;
101 }
102 
103 // Returns a new x-height maximally compatible with the result in word_res.
104 // See comment above for overall algorithm.
105 float Tesseract::ComputeCompatibleXheight(WERD_RES *word_res, float *baseline_shift) {
106  STATS top_stats(0, UINT8_MAX);
107  STATS shift_stats(-UINT8_MAX, UINT8_MAX);
108  int bottom_shift = 0;
109  int num_blobs = word_res->rebuild_word->NumBlobs();
110  do {
111  top_stats.clear();
112  shift_stats.clear();
113  for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
114  TBLOB *blob = word_res->rebuild_word->blobs[blob_id];
115  UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
116  if (unicharset.get_isalpha(class_id) || unicharset.get_isdigit(class_id)) {
117  int top = blob->bounding_box().top() + bottom_shift;
118  // Clip the top to the limit of normalized feature space.
119  if (top >= INT_FEAT_RANGE) {
120  top = INT_FEAT_RANGE - 1;
121  }
122  int bottom = blob->bounding_box().bottom() + bottom_shift;
123  int min_bottom, max_bottom, min_top, max_top;
124  unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom, &min_top, &max_top);
125  // Chars with a wild top range would mess up the result so ignore them.
126  if (max_top - min_top > kMaxCharTopRange) {
127  continue;
128  }
129  int misfit_dist = std::max((min_top - x_ht_acceptance_tolerance) - top,
130  top - (max_top + x_ht_acceptance_tolerance));
131  int height = top - kBlnBaselineOffset;
132  if (debug_x_ht_level >= 2) {
133  tprintf("Class %s: height=%d, bottom=%d,%d top=%d,%d, actual=%d,%d: ",
134  unicharset.id_to_unichar(class_id), height, min_bottom, max_bottom, min_top,
135  max_top, bottom, top);
136  }
137  // Use only chars that fit in the expected bottom range, and where
138  // the range of tops is sensibly near the xheight.
139  if (min_bottom <= bottom + x_ht_acceptance_tolerance &&
140  bottom - x_ht_acceptance_tolerance <= max_bottom && min_top > kBlnBaselineOffset &&
141  max_top - kBlnBaselineOffset >= kBlnXHeight && misfit_dist > 0) {
142  // Compute the x-height position using proportionality between the
143  // actual height and expected height.
144  int min_xht = DivRounded(height * kBlnXHeight, max_top - kBlnBaselineOffset);
145  int max_xht = DivRounded(height * kBlnXHeight, min_top - kBlnBaselineOffset);
146  if (debug_x_ht_level >= 2) {
147  tprintf(" xht range min=%d, max=%d\n", min_xht, max_xht);
148  }
149  // The range of expected heights gets a vote equal to the distance
150  // of the actual top from the expected top.
151  for (int y = min_xht; y <= max_xht; ++y) {
152  top_stats.add(y, misfit_dist);
153  }
154  } else if ((min_bottom > bottom + x_ht_acceptance_tolerance ||
155  bottom - x_ht_acceptance_tolerance > max_bottom) &&
156  bottom_shift == 0) {
157  // Get the range of required bottom shift.
158  int min_shift = min_bottom - bottom;
159  int max_shift = max_bottom - bottom;
160  if (debug_x_ht_level >= 2) {
161  tprintf(" bottom shift min=%d, max=%d\n", min_shift, max_shift);
162  }
163  // The range of expected shifts gets a vote equal to the min distance
164  // of the actual bottom from the expected bottom, spread over the
165  // range of its acceptance.
166  int misfit_weight = abs(min_shift);
167  if (max_shift > min_shift) {
168  misfit_weight /= max_shift - min_shift;
169  }
170  for (int y = min_shift; y <= max_shift; ++y) {
171  shift_stats.add(y, misfit_weight);
172  }
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 && top_stats.get_total() < shift_stats.get_total());
192  // Baseline shift is opposite sign to the bottom shift.
193  *baseline_shift = -bottom_shift / word_res->denorm.y_scale();
194  if (debug_x_ht_level >= 2) {
195  tprintf("baseline shift=%g\n", *baseline_shift);
196  }
197  if (top_stats.get_total() == 0) {
198  return bottom_shift != 0 ? word_res->x_height : 0.0f;
199  }
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", new_xht,
206  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 (std::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 
216 } // namespace tesseract
#define INT_FEAT_RANGE
Definition: float2int.h:27
void tprintf(const char *format,...)
Definition: tprintf.cpp:41
int IntCastRounded(double x)
Definition: helpers.h:175
int DivRounded(int a, int b)
Definition: helpers.h:167
const int kBlnXHeight
Definition: normalis.h:33
int UNICHAR_ID
Definition: unichar.h:36
const int kMaxCharTopRange
Definition: fixxht.cpp:69
const int kBlnBaselineOffset
Definition: normalis.h:34
float ComputeCompatibleXheight(WERD_RES *word_res, float *baseline_shift)
Definition: fixxht.cpp:105
int CountMisfitTops(WERD_RES *word_res)
Definition: fixxht.cpp:72
TBOX bounding_box() const
Definition: blobs.cpp:466
std::vector< TBLOB * > blobs
Definition: blobs.h:462
unsigned NumBlobs() const
Definition: blobs.h:449
float y_scale() const
Definition: normalis.h:262
WERD_CHOICE * best_choice
Definition: pageres.h:239
TWERD * rebuild_word
Definition: pageres.h:264
UNICHAR_ID unichar_id(unsigned index) const
Definition: ratngs.h:295
TDimension top() const
Definition: rect.h:68
TDimension bottom() const
Definition: rect.h:75
void add(int32_t value, int32_t count)
Definition: statistc.cpp:99
int32_t get_total() const
Definition: statistc.h:85
double median() const
Definition: statistc.cpp:242
UNICHARSET unicharset
Definition: ccutil.h:61
bool get_isalpha(UNICHAR_ID unichar_id) const
Definition: unicharset.h:497
const char * id_to_unichar(UNICHAR_ID id) const
Definition: unicharset.cpp:279
void get_top_bottom(UNICHAR_ID unichar_id, int *min_bottom, int *max_bottom, int *min_top, int *max_top) const
Definition: unicharset.h:586
bool get_isdigit(UNICHAR_ID unichar_id) const
Definition: unicharset.h:524