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tesseract/ccmain/osdetect.cpp

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///////////////////////////////////////////////////////////////////////
// File: osdetect.cpp
// Description: Orientation and script detection.
// Author: Samuel Charron
// Ranjith Unnikrishnan
//
// (C) Copyright 2008, Google Inc.
// 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 "osdetect.h"
#include "blobbox.h"
#include "blread.h"
#include "colfind.h"
#include "imagefind.h"
#include "linefind.h"
#include "oldlist.h"
#include "qrsequence.h"
#include "ratngs.h"
#include "strngs.h"
#include "tabvector.h"
#include "tesseractclass.h"
#include "textord.h"
#include "tstruct.h"
const int kMinCharactersToTry = 50;
const int kMaxCharactersToTry = 5 * kMinCharactersToTry;
const float kSizeRatioToReject = 2.0;
const int kMinAcceptableBlobHeight = 10;
const float kOrientationAcceptRatio = 1.3;
const float kScriptAcceptRatio = 1.3;
const float kHanRatioInKorean = 0.7;
const float kHanRatioInJapanese = 0.3;
const float kNonAmbiguousMargin = 1.0;
// General scripts
static const char* han_script = "Han";
static const char* latin_script = "Latin";
static const char* katakana_script = "Katakana";
static const char* hiragana_script = "Hiragana";
static const char* hangul_script = "Hangul";
// Pseudo-scripts Name
const char* ScriptDetector::korean_script_ = "Korean";
const char* ScriptDetector::japanese_script_ = "Japanese";
const char* ScriptDetector::fraktur_script_ = "Fraktur";
// Minimum believable resolution.
const int kMinCredibleResolution = 70;
// Default resolution used if input is not believable.
const int kDefaultResolution = 300;
void OSResults::update_best_orientation() {
float first = orientations[0];
float second = orientations[1];
best_result.orientation_id = 0;
if (orientations[0] < orientations[1]) {
first = orientations[1];
second = orientations[0];
best_result.orientation_id = 1;
}
for (int i = 2; i < 4; ++i) {
if (orientations[i] > first) {
second = first;
first = orientations[i];
best_result.orientation_id = i;
} else if (orientations[i] > second) {
second = orientations[i];
}
}
// Store difference of top two orientation scores.
best_result.oconfidence = first - second;
}
void OSResults::set_best_orientation(int orientation_id) {
best_result.orientation_id = orientation_id;
best_result.oconfidence = 0;
}
void OSResults::update_best_script(int orientation) {
// We skip index 0 to ignore the "Common" script.
float first = scripts_na[orientation][1];
float second = scripts_na[orientation][2];
best_result.script_id = 1;
if (scripts_na[orientation][1] < scripts_na[orientation][2]) {
first = scripts_na[orientation][2];
second = scripts_na[orientation][1];
best_result.script_id = 2;
}
for (int i = 3; i < kMaxNumberOfScripts; ++i) {
if (scripts_na[orientation][i] > first) {
best_result.script_id = i;
second = first;
first = scripts_na[orientation][i];
} else if (scripts_na[orientation][i] > second) {
second = scripts_na[orientation][i];
}
}
best_result.sconfidence =
(first / second - 1.0) / (kScriptAcceptRatio - 1.0);
}
// Detect and erase horizontal/vertical lines and picture regions from the
// image, so that non-text blobs are removed from consideration.
void remove_nontext_regions(tesseract::Tesseract *tess, BLOCK_LIST *blocks,
TO_BLOCK_LIST *to_blocks) {
Pix *pix = tess->pix_binary();
ASSERT_HOST(pix != NULL);
int vertical_x = 0;
int vertical_y = 1;
tesseract::TabVector_LIST v_lines;
tesseract::TabVector_LIST h_lines;
Boxa* boxa = NULL;
Pixa* pixa = NULL;
const int kMinCredibleResolution = 70;
int resolution = (kMinCredibleResolution > pixGetXRes(pix)) ?
kMinCredibleResolution : pixGetXRes(pix);
tesseract::LineFinder::FindVerticalLines(resolution, pix, &vertical_x,
&vertical_y, &v_lines);
tesseract::LineFinder::FindHorizontalLines(resolution, pix, &h_lines);
tesseract::ImageFinder::FindImages(pix, &boxa, &pixa);
pixaDestroy(&pixa);
boxaDestroy(&boxa);
tess->mutable_textord()->find_components(tess->pix_binary(),
blocks, to_blocks);
}
// Find connected components in the page and process a subset until finished or
// a stopping criterion is met.
// Returns the number of blobs used in making the estimate. 0 implies failure.
int orientation_and_script_detection(STRING& filename,
OSResults* osr,
tesseract::Tesseract* tess) {
STRING name = filename; //truncated name
const char *lastdot; //of name
TBOX page_box;
lastdot = strrchr (name.string (), '.');
if (lastdot != NULL)
name[lastdot-name.string()] = '\0';
ASSERT_HOST(tess->pix_binary() != NULL)
int width = pixGetWidth(tess->pix_binary());
int height = pixGetHeight(tess->pix_binary());
int resolution = pixGetXRes(tess->pix_binary());
// Zero resolution messes up the algorithms, so make sure it is credible.
if (resolution < kMinCredibleResolution)
resolution = kDefaultResolution;
BLOCK_LIST blocks;
if (!read_unlv_file(name, width, height, &blocks))
FullPageBlock(width, height, &blocks);
// Try to remove non-text regions from consideration.
TO_BLOCK_LIST land_blocks, port_blocks;
remove_nontext_regions(tess, &blocks, &port_blocks);
if (port_blocks.empty()) {
// page segmentation did not succeed, so we need to find_components first.
tess->mutable_textord()->find_components(tess->pix_binary(),
&blocks, &port_blocks);
} else {
page_box.set_left(0);
page_box.set_bottom(0);
page_box.set_right(width);
page_box.set_top(height);
// Filter_blobs sets up the TO_BLOCKs the same as find_components does.
tess->mutable_textord()->filter_blobs(page_box.topright(),
&port_blocks, true);
}
return os_detect(&port_blocks, osr, tess);
}
// Filter and sample the blobs.
// Returns a non-zero number of blobs if the page was successfully processed, or
// zero if the page had too few characters to be reliable
int os_detect(TO_BLOCK_LIST* port_blocks, OSResults* osr,
tesseract::Tesseract* tess) {
int blobs_total = 0;
TO_BLOCK_IT block_it;
block_it.set_to_list(port_blocks);
BLOBNBOX_CLIST filtered_list;
BLOBNBOX_C_IT filtered_it(&filtered_list);
for (block_it.mark_cycle_pt(); !block_it.cycled_list();
block_it.forward ()) {
TO_BLOCK* to_block = block_it.data();
if (to_block->block->poly_block() &&
!to_block->block->poly_block()->IsText()) continue;
BLOBNBOX_IT bbox_it;
bbox_it.set_to_list(&to_block->blobs);
for (bbox_it.mark_cycle_pt (); !bbox_it.cycled_list ();
bbox_it.forward ()) {
BLOBNBOX* bbox = bbox_it.data();
C_BLOB* blob = bbox->cblob();
TBOX box = blob->bounding_box();
++blobs_total;
float y_x = fabs((box.height() * 1.0) / box.width());
float x_y = 1.0f / y_x;
// Select a >= 1.0 ratio
float ratio = x_y > y_x ? x_y : y_x;
// Blob is ambiguous
if (ratio > kSizeRatioToReject) continue;
if (box.height() < kMinAcceptableBlobHeight) continue;
filtered_it.add_to_end(bbox);
}
}
return os_detect_blobs(&filtered_list, osr, tess);
}
// Detect orientation and script from a list of blobs.
// Returns a non-zero number of blobs if the list was successfully processed, or
// zero if the list had too few characters to be reliable
int os_detect_blobs(BLOBNBOX_CLIST* blob_list, OSResults* osr,
tesseract::Tesseract* tess) {
OSResults osr_;
if (osr == NULL)
osr = &osr_;
osr->unicharset = &tess->unicharset;
OrientationDetector o(osr);
ScriptDetector s(osr, tess);
BLOBNBOX_C_IT filtered_it(blob_list);
int real_max = MIN(filtered_it.length(), kMaxCharactersToTry);
// printf("Total blobs found = %d\n", blobs_total);
// printf("Number of blobs post-filtering = %d\n", filtered_it.length());
// printf("Number of blobs to try = %d\n", real_max);
// If there are too few characters, skip this page entirely.
if (real_max < kMinCharactersToTry / 2) {
printf("Too few characters. Skipping this page\n");
return 0;
}
BLOBNBOX** blobs = new BLOBNBOX*[filtered_it.length()];
int number_of_blobs = 0;
for (filtered_it.mark_cycle_pt (); !filtered_it.cycled_list ();
filtered_it.forward ()) {
blobs[number_of_blobs++] = (BLOBNBOX*)filtered_it.data();
}
QRSequenceGenerator sequence(number_of_blobs);
int num_blobs_evaluated = 0;
for (int i = 0; i < real_max; ++i) {
if (os_detect_blob(blobs[sequence.GetVal()], &o, &s, osr, tess)
&& i > kMinCharactersToTry) {
break;
}
++num_blobs_evaluated;
}
delete [] blobs;
// Make sure the best_result is up-to-date
int orientation = o.get_orientation();
osr->update_best_script(orientation);
return num_blobs_evaluated;
}
// Processes a single blob to estimate script and orientation.
// Return true if estimate of orientation and script satisfies stopping
// criteria.
bool os_detect_blob(BLOBNBOX* bbox, OrientationDetector* o,
ScriptDetector* s, OSResults* osr,
tesseract::Tesseract* tess) {
C_BLOB* blob = bbox->cblob();
TBOX box = blob->bounding_box();
int x_mid = (box.left() + box.right()) / 2.0f;
int y_mid = (box.bottom() + box.top()) / 2.0f;
PBLOB pblob(blob);
BLOB_CHOICE_LIST ratings[4];
// Test the 4 orientations
for (int i = 0; i < 4; ++i) {
// normalize the blob
float scaling = static_cast<float>(kBlnXHeight) / box.height();
DENORM denorm(x_mid, scaling, 0.0, box.bottom(), 0, NULL, false, NULL);
pblob.move(FCOORD(-x_mid, -box.bottom()));
pblob.scale(scaling);
pblob.move(FCOORD(0.0f, kBlnBaselineOffset));
{
// List of choices given by the classifier
tess->tess_cn_matching.set_value(true); // turn it on
tess->tess_bn_matching.set_value(false);
// Convert blob
TBLOB* tessblob = make_tess_blob(&pblob);
// Classify
tess->set_denorm(&denorm);
tess->AdaptiveClassifier(tessblob, ratings + i, NULL);
delete tessblob;
}
// undo normalize
pblob.move(FCOORD(0.0f, -kBlnBaselineOffset));
pblob.scale(1.0f / scaling);
pblob.move(FCOORD(x_mid, box.bottom()));
// center the blob
pblob.move(FCOORD(-x_mid, -y_mid));
// TODO(rays) Although we should now get the correct image coords with
// the DENORM, there is nothing to tell the classifier to rotate the
// image or to actually rotate the image for it.
// Rotate it
pblob.rotate();
// Re-compute the mid
box = pblob.bounding_box();
x_mid = (box.left() + box.right()) / 2;
y_mid = (box.top() + box.bottom()) / 2;
// re-center in the new mid
pblob.move(FCOORD(x_mid, y_mid));
}
bool stop = o->detect_blob(ratings);
s->detect_blob(ratings);
int orientation = o->get_orientation();
stop = s->must_stop(orientation) && stop;
return stop;
}
OrientationDetector::OrientationDetector(OSResults* osr) {
osr_ = osr;
}
// Score the given blob and return true if it is now sure of the orientation
// after adding this block.
bool OrientationDetector::detect_blob(BLOB_CHOICE_LIST* scores) {
float blob_o_score[4] = {0.0, 0.0, 0.0, 0.0};
float total_blob_o_score = 0.0;
for (int i = 0; i < 4; ++i) {
BLOB_CHOICE_IT choice_it;
choice_it.set_to_list(scores + i);
if (!choice_it.empty()) {
// The certainty score ranges between [-20,0]. This is converted here to
// [0,1], with 1 indicating best match.
blob_o_score[i] = 1 + 0.05 * choice_it.data()->certainty();
total_blob_o_score += blob_o_score[i];
}
}
// Normalize the orientation scores for the blob and use them to
// update the aggregated orientation score.
for (int i = 0; total_blob_o_score != 0 && i < 4; ++i) {
osr_->orientations[i] += log(blob_o_score[i] / total_blob_o_score);
}
float first = -1;
float second = -1;
int idx = -1;
for (int i = 0; i < 4; ++i) {
if (osr_->orientations[i] > first) {
idx = i;
second = first;
first = osr_->orientations[i];
} else if (osr_->orientations[i] > second) {
second = osr_->orientations[i];
}
}
return first / second > kOrientationAcceptRatio;
}
int OrientationDetector::get_orientation() {
osr_->update_best_orientation();
return osr_->best_result.orientation_id;
}
ScriptDetector::ScriptDetector(OSResults* osr, tesseract::Tesseract* tess) {
osr_ = osr;
tess_ = tess;
katakana_id_ = tess_->unicharset.add_script(katakana_script);
hiragana_id_ = tess_->unicharset.add_script(hiragana_script);
han_id_ = tess_->unicharset.add_script(han_script);
hangul_id_ = tess_->unicharset.add_script(hangul_script);
japanese_id_ = tess_->unicharset.add_script(japanese_script_);
korean_id_ = tess_->unicharset.add_script(korean_script_);
latin_id_ = tess_->unicharset.add_script(latin_script);
fraktur_id_ = tess_->unicharset.add_script(fraktur_script_);
}
// Score the given blob and return true if it is now sure of the script after
// adding this blob.
void ScriptDetector::detect_blob(BLOB_CHOICE_LIST* scores) {
bool done[kMaxNumberOfScripts];
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < kMaxNumberOfScripts; ++j)
done[j] = false;
BLOB_CHOICE_IT choice_it;
choice_it.set_to_list(scores + i);
float prev_score = -1;
int script_count = 0;
int prev_id = -1;
int prev_script;
int prev_class_id = -1;
int prev_config = -1;
const char* prev_unichar = "";
const char* unichar = "";
float next_best_score = -1.0;
int next_best_script_id = -1;
const char* next_best_unichar = "";
for (choice_it.mark_cycle_pt(); !choice_it.cycled_list();
choice_it.forward()) {
BLOB_CHOICE* choice = choice_it.data();
int id = choice->script_id();
// Script already processed before.
if (done[id]) continue;
done[id] = true;
unichar = tess_->unicharset.id_to_unichar(choice->unichar_id());
// Save data from the first match
if (prev_score < 0) {
prev_score = -choice->certainty();
script_count = 1;
prev_id = id;
prev_script = choice->script_id();
prev_unichar = unichar;
prev_class_id = choice->unichar_id();
prev_config = choice->config();
} else if (-choice->certainty() < prev_score + kNonAmbiguousMargin) {
++script_count;
next_best_score = -choice->certainty();
next_best_script_id = choice->script_id();
next_best_unichar = tess_->unicharset.id_to_unichar(choice->unichar_id());
}
if (strlen(prev_unichar) == 1)
if (unichar[0] >= '0' && unichar[0] <= '9')
break;
// if script_count is >= 2, character is ambiguous, skip other matches
// since they are useless.
if (script_count >= 2)
break;
}
// Character is non ambiguous
if (script_count == 1) {
// Update the score of the winning script
osr_->scripts_na[i][prev_id] += 1.0;
// Workaround for Fraktur
if (prev_id == latin_id_) {
int font_set_id = tess_->PreTrainedTemplates->
Class[prev_class_id]->font_set_id;
if (font_set_id >= 0 && prev_config >= 0) {
FontInfo fi = tess_->get_fontinfo_table().get(
tess_->get_fontset_table().get(font_set_id).configs[prev_config]);
//printf("Font: %s i:%i b:%i f:%i s:%i k:%i (%s)\n", fi.name,
// fi.is_italic(), fi.is_bold(), fi.is_fixed_pitch(),
// fi.is_serif(), fi.is_fraktur(),
// prev_unichar);
if (fi.is_fraktur()) {
osr_->scripts_na[i][prev_id] -= 1.0;
osr_->scripts_na[i][fraktur_id_] += 1.0;
}
}
}
// Update Japanese / Korean pseudo-scripts
if (prev_id == katakana_id_)
osr_->scripts_na[i][japanese_id_] += 1.0;
if (prev_id == hiragana_id_)
osr_->scripts_na[i][japanese_id_] += 1.0;
if (prev_id == hangul_id_)
osr_->scripts_na[i][korean_id_] += 1.0;
if (prev_id == han_id_)
osr_->scripts_na[i][korean_id_] += kHanRatioInKorean;
if (prev_id == han_id_)
osr_->scripts_na[i][japanese_id_] += kHanRatioInJapanese;
}
} // iterate over each orientation
}
bool ScriptDetector::must_stop(int orientation) {
osr_->update_best_script(orientation);
return osr_->best_result.sconfidence > 1;
}
// Helper method to convert an orientation index to its value in degrees.
// The value represents the amount of clockwise rotation in degrees that must be
// applied for the text to be upright (readable).
const int OrientationIdToValue(const int& id) {
switch (id) {
case 0:
return 0;
case 1:
return 270;
case 2:
return 180;
case 3:
return 90;
default:
return -1;
}
}
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