forked from tesseract-ocr/tesseract
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathfixxht.cpp
214 lines (207 loc) · 10.1 KB
/
fixxht.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
/**********************************************************************
* File: fixxht.cpp (Formerly fixxht.c)
* Description: Improve x_ht and look out for case inconsistencies
* Author: Phil Cheatle
* Created: Thu Aug 5 14:11:08 BST 1993
*
* (C) Copyright 1992, Hewlett-Packard Ltd.
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
** http://www.apache.org/licenses/LICENSE-2.0
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*
**********************************************************************/
#include <string.h>
#include <ctype.h>
#include "params.h"
#include "float2int.h"
#include "tesseractclass.h"
namespace tesseract {
// Fixxht overview.
// Premise: Initial estimate of x-height is adequate most of the time, but
// occasionally it is incorrect. Most notable causes of failure are:
// 1. Small caps, where the top of the caps is the same as the body text
// xheight. For small caps words the xheight needs to be reduced to correctly
// recognize the caps in the small caps word.
// 2. All xheight lines, such as summer. Here the initial estimate will have
// guessed that the blob tops are caps and will have placed the xheight too low.
// 3. Noise/logos beside words, or changes in font size on a line. Such
// things can blow the statistics and cause an incorrect estimate.
// 4. Incorrect baseline. Can happen when 2 columns are incorrectly merged.
// In this case the x-height is often still correct.
//
// Algorithm.
// Compare the vertical position (top only) of alphnumerics in a word with
// the range of positions in training data (in the unicharset).
// See CountMisfitTops. If any characters disagree sufficiently with the
// initial xheight estimate, then recalculate the xheight, re-run OCR on
// the word, and if the number of vertical misfits goes down, along with
// either the word rating or certainty, then keep the new xheight.
// The new xheight is calculated as follows:ComputeCompatibleXHeight
// For each alphanumeric character that has a vertically misplaced top
// (a misfit), yet its bottom is within the acceptable range (ie it is not
// likely a sub-or super-script) calculate the range of acceptable xheight
// positions from its range of tops, and give each value in the range a
// number of votes equal to the distance of its top from its acceptance range.
// The x-height position with the median of the votes becomes the new
// x-height. This assumes that most characters will be correctly recognized
// even if the x-height is incorrect. This is not a terrible assumption, but
// it is not great. An improvement would be to use a classifier that does
// not care about vertical position or scaling at all.
// Separately collect stats on shifted baselines and apply the same logic to
// computing a best-fit shift to fix the error. If the baseline needs to be
// shifted, but the x-height is OK, returns the original x-height along with
// the baseline shift to indicate that recognition needs to re-run.
// If the max-min top of a unicharset char is bigger than kMaxCharTopRange
// then the char top cannot be used to judge misfits or suggest a new top.
const int kMaxCharTopRange = 48;
// Returns the number of misfit blob tops in this word.
int Tesseract::CountMisfitTops(WERD_RES *word_res) {
int bad_blobs = 0;
int num_blobs = word_res->rebuild_word->NumBlobs();
for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
TBLOB* blob = word_res->rebuild_word->blobs[blob_id];
UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
if (unicharset.get_isalpha(class_id) || unicharset.get_isdigit(class_id)) {
int top = blob->bounding_box().top();
if (top >= INT_FEAT_RANGE)
top = INT_FEAT_RANGE - 1;
int min_bottom, max_bottom, min_top, max_top;
unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom,
&min_top, &max_top);
if (max_top - min_top > kMaxCharTopRange)
continue;
bool bad = top < min_top - x_ht_acceptance_tolerance ||
top > max_top + x_ht_acceptance_tolerance;
if (bad)
++bad_blobs;
if (debug_x_ht_level >= 1) {
tprintf("Class %s is %s with top %d vs limits of %d->%d, +/-%d\n",
unicharset.id_to_unichar(class_id),
bad ? "Misfit" : "OK", top, min_top, max_top,
static_cast<int>(x_ht_acceptance_tolerance));
}
}
}
return bad_blobs;
}
// Returns a new x-height maximally compatible with the result in word_res.
// See comment above for overall algorithm.
float Tesseract::ComputeCompatibleXheight(WERD_RES *word_res,
float* baseline_shift) {
STATS top_stats(0, UINT8_MAX);
STATS shift_stats(-UINT8_MAX, UINT8_MAX);
int bottom_shift = 0;
int num_blobs = word_res->rebuild_word->NumBlobs();
do {
top_stats.clear();
shift_stats.clear();
for (int blob_id = 0; blob_id < num_blobs; ++blob_id) {
TBLOB* blob = word_res->rebuild_word->blobs[blob_id];
UNICHAR_ID class_id = word_res->best_choice->unichar_id(blob_id);
if (unicharset.get_isalpha(class_id) ||
unicharset.get_isdigit(class_id)) {
int top = blob->bounding_box().top() + bottom_shift;
// Clip the top to the limit of normalized feature space.
if (top >= INT_FEAT_RANGE)
top = INT_FEAT_RANGE - 1;
int bottom = blob->bounding_box().bottom() + bottom_shift;
int min_bottom, max_bottom, min_top, max_top;
unicharset.get_top_bottom(class_id, &min_bottom, &max_bottom,
&min_top, &max_top);
// Chars with a wild top range would mess up the result so ignore them.
if (max_top - min_top > kMaxCharTopRange)
continue;
int misfit_dist = MAX((min_top - x_ht_acceptance_tolerance) - top,
top - (max_top + x_ht_acceptance_tolerance));
int height = top - kBlnBaselineOffset;
if (debug_x_ht_level >= 2) {
tprintf("Class %s: height=%d, bottom=%d,%d top=%d,%d, actual=%d,%d: ",
unicharset.id_to_unichar(class_id),
height, min_bottom, max_bottom, min_top, max_top,
bottom, top);
}
// Use only chars that fit in the expected bottom range, and where
// the range of tops is sensibly near the xheight.
if (min_bottom <= bottom + x_ht_acceptance_tolerance &&
bottom - x_ht_acceptance_tolerance <= max_bottom &&
min_top > kBlnBaselineOffset &&
max_top - kBlnBaselineOffset >= kBlnXHeight &&
misfit_dist > 0) {
// Compute the x-height position using proportionality between the
// actual height and expected height.
int min_xht = DivRounded(height * kBlnXHeight,
max_top - kBlnBaselineOffset);
int max_xht = DivRounded(height * kBlnXHeight,
min_top - kBlnBaselineOffset);
if (debug_x_ht_level >= 2) {
tprintf(" xht range min=%d, max=%d\n", min_xht, max_xht);
}
// The range of expected heights gets a vote equal to the distance
// of the actual top from the expected top.
for (int y = min_xht; y <= max_xht; ++y)
top_stats.add(y, misfit_dist);
} else if ((min_bottom > bottom + x_ht_acceptance_tolerance ||
bottom - x_ht_acceptance_tolerance > max_bottom) &&
bottom_shift == 0) {
// Get the range of required bottom shift.
int min_shift = min_bottom - bottom;
int max_shift = max_bottom - bottom;
if (debug_x_ht_level >= 2) {
tprintf(" bottom shift min=%d, max=%d\n", min_shift, max_shift);
}
// The range of expected shifts gets a vote equal to the min distance
// of the actual bottom from the expected bottom, spread over the
// range of its acceptance.
int misfit_weight = abs(min_shift);
if (max_shift > min_shift)
misfit_weight /= max_shift - min_shift;
for (int y = min_shift; y <= max_shift; ++y)
shift_stats.add(y, misfit_weight);
} else {
if (bottom_shift == 0) {
// Things with bottoms that are already ok need to say so, on the
// 1st iteration only.
shift_stats.add(0, kBlnBaselineOffset);
}
if (debug_x_ht_level >= 2) {
tprintf(" already OK\n");
}
}
}
}
if (shift_stats.get_total() > top_stats.get_total()) {
bottom_shift = IntCastRounded(shift_stats.median());
if (debug_x_ht_level >= 2) {
tprintf("Applying bottom shift=%d\n", bottom_shift);
}
}
} while (bottom_shift != 0 &&
top_stats.get_total() < shift_stats.get_total());
// Baseline shift is opposite sign to the bottom shift.
*baseline_shift = -bottom_shift / word_res->denorm.y_scale();
if (debug_x_ht_level >= 2) {
tprintf("baseline shift=%g\n", *baseline_shift);
}
if (top_stats.get_total() == 0)
return bottom_shift != 0 ? word_res->x_height : 0.0f;
// The new xheight is just the median vote, which is then scaled out
// of BLN space back to pixel space to get the x-height in pixel space.
float new_xht = top_stats.median();
if (debug_x_ht_level >= 2) {
tprintf("Median xht=%f\n", new_xht);
tprintf("Mode20:A: New x-height = %f (norm), %f (orig)\n",
new_xht, new_xht / word_res->denorm.y_scale());
}
// The xheight must change by at least x_ht_min_change to be used.
if (fabs(new_xht - kBlnXHeight) >= x_ht_min_change)
return new_xht / word_res->denorm.y_scale();
else
return bottom_shift != 0 ? word_res->x_height : 0.0f;
}
} // namespace tesseract