tesseract  5.0.0
associate.cpp
Go to the documentation of this file.
1 // File: associate.cpp
3 // Description: Functions for scoring segmentation paths according to
4 // their character widths, gap widths and seam cuts.
5 // Author: Daria Antonova
6 // Created: Mon Mar 8 11:26:43 PDT 2010
7 //
8 // (C) Copyright 2010, Google Inc.
9 // Licensed under the Apache License, Version 2.0 (the "License");
10 // you may not use this file except in compliance with the License.
11 // You may obtain a copy of the License at
12 // http://www.apache.org/licenses/LICENSE-2.0
13 // Unless required by applicable law or agreed to in writing, software
14 // distributed under the License is distributed on an "AS IS" BASIS,
15 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 // See the License for the specific language governing permissions and
17 // limitations under the License.
18 //
20 
21 #include <cmath>
22 #include <cstdio>
23 
24 #include "associate.h"
25 #include "normalis.h"
26 #include "pageres.h"
27 
28 namespace tesseract {
29 
31 const float AssociateUtils::kMinGap = 0.03f;
32 
33 void AssociateUtils::ComputeStats(int col, int row, const AssociateStats *parent_stats,
34  int parent_path_length, bool fixed_pitch, float max_char_wh_ratio,
35  WERD_RES *word_res, bool debug, AssociateStats *stats) {
36  stats->Clear();
37 
38  ASSERT_HOST(word_res != nullptr);
39  if (word_res->blob_widths.empty()) {
40  return;
41  }
42  if (debug) {
43  tprintf("AssociateUtils::ComputeStats() for col=%d, row=%d%s\n", col, row,
44  fixed_pitch ? " (fixed pitch)" : "");
45  }
46  float normalizing_height = kBlnXHeight;
47  ROW *blob_row = word_res->blob_row;
48  // TODO(rays/daria) Can unicharset.script_has_xheight be useful here?
49  if (fixed_pitch && blob_row != nullptr) {
50  // For fixed pitch language like CJK, we use the full text height
51  // as the normalizing factor so we are not dependent on xheight
52  // calculation.
53  if (blob_row->body_size() > 0.0f) {
54  normalizing_height = word_res->denorm.y_scale() * blob_row->body_size();
55  } else {
56  normalizing_height =
57  word_res->denorm.y_scale() * (blob_row->x_height() + blob_row->ascenders());
58  }
59  if (debug) {
60  tprintf("normalizing height = %g (scale %g xheight %g ascenders %g)\n", normalizing_height,
61  word_res->denorm.y_scale(), blob_row->x_height(), blob_row->ascenders());
62  }
63  }
64  float wh_ratio = word_res->GetBlobsWidth(col, row) / normalizing_height;
65  if (wh_ratio > max_char_wh_ratio) {
66  stats->bad_shape = true;
67  }
68  // Compute the gap sum for this shape. If there are only negative or only
69  // positive gaps, record their sum in stats->gap_sum. However, if there is
70  // a mixture, record only the sum of the positive gaps.
71  // TODO(antonova): explain fragment.
72  int negative_gap_sum = 0;
73  for (int c = col; c < row; ++c) {
74  int gap = word_res->GetBlobsGap(c);
75  (gap > 0) ? stats->gap_sum += gap : negative_gap_sum += gap;
76  }
77  if (stats->gap_sum == 0) {
78  stats->gap_sum = negative_gap_sum;
79  }
80  if (debug) {
81  tprintf("wh_ratio=%g (max_char_wh_ratio=%g) gap_sum=%d %s\n", wh_ratio, max_char_wh_ratio,
82  stats->gap_sum, stats->bad_shape ? "bad_shape" : "");
83  }
84  // Compute shape_cost (for fixed pitch mode).
85  if (fixed_pitch) {
86  bool end_row = (row == (word_res->ratings->dimension() - 1));
87 
88  // Ensure that the blob has gaps on the left and the right sides
89  // (except for beginning and ending punctuation) and that there is
90  // no cutting through ink at the blob boundaries.
91  if (col > 0) {
92  float left_gap = word_res->GetBlobsGap(col - 1) / normalizing_height;
93  SEAM *left_seam = word_res->seam_array[col - 1];
94  if ((!end_row && left_gap < kMinGap) || left_seam->priority() > 0.0f) {
95  stats->bad_shape = true;
96  }
97  if (debug) {
98  tprintf("left_gap %g, left_seam %g %s\n", left_gap, left_seam->priority(),
99  stats->bad_shape ? "bad_shape" : "");
100  }
101  }
102  float right_gap = 0.0f;
103  if (!end_row) {
104  right_gap = word_res->GetBlobsGap(row) / normalizing_height;
105  SEAM *right_seam = word_res->seam_array[row];
106  if (right_gap < kMinGap || right_seam->priority() > 0.0f) {
107  stats->bad_shape = true;
108  if (right_gap < kMinGap) {
109  stats->bad_fixed_pitch_right_gap = true;
110  }
111  }
112  if (debug) {
113  tprintf("right_gap %g right_seam %g %s\n", right_gap, right_seam->priority(),
114  stats->bad_shape ? "bad_shape" : "");
115  }
116  }
117 
118  // Impose additional segmentation penalties if blob widths or gaps
119  // distribution don't fit a fixed-pitch model.
120  // Since we only know the widths and gaps of the path explored so far,
121  // the means and variances are computed for the path so far (not
122  // considering characters to the right of the last character on the path).
123  stats->full_wh_ratio = wh_ratio + right_gap;
124  if (parent_stats != nullptr) {
125  stats->full_wh_ratio_total = (parent_stats->full_wh_ratio_total + stats->full_wh_ratio);
126  float mean = stats->full_wh_ratio_total / static_cast<float>(parent_path_length + 1);
127  stats->full_wh_ratio_var =
128  parent_stats->full_wh_ratio_var + pow(mean - stats->full_wh_ratio, 2);
129  } else {
130  stats->full_wh_ratio_total = stats->full_wh_ratio;
131  }
132  if (debug) {
133  tprintf("full_wh_ratio %g full_wh_ratio_total %g full_wh_ratio_var %g\n",
134  stats->full_wh_ratio, stats->full_wh_ratio_total, stats->full_wh_ratio_var);
135  }
136 
137  stats->shape_cost = FixedPitchWidthCost(wh_ratio, right_gap, end_row, max_char_wh_ratio);
138 
139  // For some reason Tesseract prefers to treat the whole CJ words
140  // as one blob when the initial segmentation is particularly bad.
141  // This hack is to avoid favoring such states.
142  if (col == 0 && end_row && wh_ratio > max_char_wh_ratio) {
143  stats->shape_cost += 10;
144  }
145  stats->shape_cost += stats->full_wh_ratio_var;
146  if (debug) {
147  tprintf("shape_cost %g\n", stats->shape_cost);
148  }
149  }
150 }
151 
152 float AssociateUtils::FixedPitchWidthCost(float norm_width, float right_gap, bool end_pos,
153  float max_char_wh_ratio) {
154  float cost = 0.0f;
155  if (norm_width > max_char_wh_ratio) {
156  cost += norm_width;
157  }
158  if (norm_width > kMaxFixedPitchCharAspectRatio) {
159  cost += norm_width * norm_width; // extra penalty for merging CJK chars
160  }
161  // Penalize skinny blobs, except for punctuation in the last position.
162  if (norm_width + right_gap < 0.5f && !end_pos) {
163  cost += 1.0f - (norm_width + right_gap);
164  }
165  return cost;
166 }
167 
168 } // namespace tesseract
#define ASSERT_HOST(x)
Definition: errcode.h:59
void tprintf(const char *format,...)
Definition: tprintf.cpp:41
const int kBlnXHeight
Definition: normalis.h:33
int dimension() const
Definition: matrix.h:612
float y_scale() const
Definition: normalis.h:262
float body_size() const
Definition: ocrrow.h:75
float x_height() const
Definition: ocrrow.h:66
float ascenders() const
Definition: ocrrow.h:84
int GetBlobsGap(unsigned blob_index) const
Definition: pageres.cpp:757
MATRIX * ratings
Definition: pageres.h:235
std::vector< int > blob_widths
Definition: pageres.h:214
int GetBlobsWidth(int start_blob, int last_blob) const
Definition: pageres.cpp:746
std::vector< SEAM * > seam_array
Definition: pageres.h:212
float priority() const
Definition: seam.h:46
static const float kMaxFixedPitchCharAspectRatio
Definition: associate.h:73
static const float kMinGap
Definition: associate.h:74
static float FixedPitchWidthCost(float norm_width, float right_gap, bool end_pos, float max_char_wh_ratio)
Definition: associate.cpp:152
static void ComputeStats(int col, int row, const AssociateStats *parent_stats, int parent_path_length, bool fixed_pitch, float max_char_wh_ratio, WERD_RES *word_res, bool debug, AssociateStats *stats)
Definition: associate.cpp:33