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tesseract/classify/intfx.cpp

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/******************************************************************************
** Filename: intfx.c
** Purpose: Integer character normalization & feature extraction
** Author: Robert Moss, rays@google.com (Ray Smith)
** History: Tue May 21 15:51:57 MDT 1991, RWM, Created.
** Tue Feb 28 10:42:00 PST 2012, vastly rewritten to allow
greyscale fx and non-linear
normalization.
**
** (c) Copyright Hewlett-Packard Company, 1988.
** 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 Files and Type Defines
----------------------------------------------------------------------------**/
#include "intfx.h"
#include "allheaders.h"
#include "ccutil.h"
#include "classify.h"
#include "const.h"
#include "helpers.h"
#include "intmatcher.h"
#include "linlsq.h"
#include "ndminx.h"
#include "normalis.h"
#include "statistc.h"
#include "trainingsample.h"
using tesseract::TrainingSample;
/**----------------------------------------------------------------------------
Global Data Definitions and Declarations
----------------------------------------------------------------------------**/
// Look up table for cos and sin to turn the intfx feature angle to a vector.
// Protected by atan_table_mutex.
// The entries are in binary degrees where a full circle is 256 binary degrees.
static float cos_table[INT_CHAR_NORM_RANGE];
static float sin_table[INT_CHAR_NORM_RANGE];
// Guards write access to AtanTable so we dont create it more than once.
tesseract::CCUtilMutex atan_table_mutex;
/**----------------------------------------------------------------------------
Public Code
----------------------------------------------------------------------------**/
/*---------------------------------------------------------------------------*/
void InitIntegerFX() {
static bool atan_table_init = false;
atan_table_mutex.Lock();
if (!atan_table_init) {
for (int i = 0; i < INT_CHAR_NORM_RANGE; ++i) {
cos_table[i] = cos(i * 2 * PI / INT_CHAR_NORM_RANGE + PI);
sin_table[i] = sin(i * 2 * PI / INT_CHAR_NORM_RANGE + PI);
}
atan_table_init = true;
}
atan_table_mutex.Unlock();
}
// Returns a vector representing the direction of a feature with the given
// theta direction in an INT_FEATURE_STRUCT.
FCOORD FeatureDirection(uinT8 theta) {
return FCOORD(cos_table[theta], sin_table[theta]);
}
namespace tesseract {
// Generates a TrainingSample from a TBLOB. Extracts features and sets
// the bounding box, so classifiers that operate on the image can work.
// TODO(rays) BlobToTrainingSample must remain a global function until
// the FlexFx and FeatureDescription code can be removed and LearnBlob
// made a member of Classify.
TrainingSample* BlobToTrainingSample(const TBLOB& blob,
tesseract::NormalizationMode mode,
bool nonlinear_norm) {
INT_FX_RESULT_STRUCT fx_info;
GenericVector<INT_FEATURE_STRUCT> bl_features;
GenericVector<INT_FEATURE_STRUCT> cn_features;
Classify::ExtractFeatures(blob, nonlinear_norm, &bl_features,
&cn_features, &fx_info, NULL);
// TODO(rays) Use blob->PreciseBoundingBox() instead.
TBOX box = blob.bounding_box();
TrainingSample* sample = NULL;
if (mode == tesseract::NM_CHAR_ANISOTROPIC) {
int num_features = fx_info.NumCN;
if (num_features > 0) {
sample = TrainingSample::CopyFromFeatures(fx_info, box, &cn_features[0],
num_features);
}
} else if (mode == tesseract::NM_BASELINE) {
int num_features = fx_info.NumBL;
if (num_features > 0) {
sample = TrainingSample::CopyFromFeatures(fx_info, box, &bl_features[0],
num_features);
}
} else {
ASSERT_HOST(!"Unsupported normalization mode!");
}
if (sample != NULL) {
// Set the bounding box (in original image coordinates) in the sample.
TPOINT topleft, botright;
topleft.x = box.left();
topleft.y = box.top();
botright.x = box.right();
botright.y = box.bottom();
TPOINT original_topleft, original_botright;
blob.denorm().DenormTransform(NULL, topleft, &original_topleft);
blob.denorm().DenormTransform(NULL, botright, &original_botright);
sample->set_bounding_box(TBOX(original_topleft.x, original_botright.y,
original_botright.x, original_topleft.y));
}
return sample;
}
// Computes the DENORMS for bl(baseline) and cn(character) normalization
// during feature extraction. The input denorm describes the current state
// of the blob, which is usually a baseline-normalized word.
// The Transforms setup are as follows:
// Baseline Normalized (bl) Output:
// We center the grapheme by aligning the x-coordinate of its centroid with
// x=128 and leaving the already-baseline-normalized y as-is.
//
// Character Normalized (cn) Output:
// We align the grapheme's centroid at the origin and scale it
// asymmetrically in x and y so that the 2nd moments are a standard value
// (51.2) ie the result is vaguely square.
// If classify_nonlinear_norm is true:
// A non-linear normalization is setup that attempts to evenly distribute
// edges across x and y.
//
// Some of the fields of fx_info are also setup:
// Length: Total length of outline.
// Rx: Rounded y second moment. (Reversed by convention.)
// Ry: rounded x second moment.
// Xmean: Rounded x center of mass of the blob.
// Ymean: Rounded y center of mass of the blob.
void Classify::SetupBLCNDenorms(const TBLOB& blob, bool nonlinear_norm,
DENORM* bl_denorm, DENORM* cn_denorm,
INT_FX_RESULT_STRUCT* fx_info) {
// Compute 1st and 2nd moments of the original outline.
FCOORD center, second_moments;
int length = blob.ComputeMoments(&center, &second_moments);
if (fx_info != NULL) {
fx_info->Length = length;
fx_info->Rx = IntCastRounded(second_moments.y());
fx_info->Ry = IntCastRounded(second_moments.x());
fx_info->Xmean = IntCastRounded(center.x());
fx_info->Ymean = IntCastRounded(center.y());
}
// Setup the denorm for Baseline normalization.
bl_denorm->SetupNormalization(NULL, NULL, &blob.denorm(), center.x(), 128.0f,
1.0f, 1.0f, 128.0f, 128.0f);
// Setup the denorm for character normalization.
if (nonlinear_norm) {
GenericVector<GenericVector<int> > x_coords;
GenericVector<GenericVector<int> > y_coords;
TBOX box;
blob.GetPreciseBoundingBox(&box);
box.pad(1, 1);
blob.GetEdgeCoords(box, &x_coords, &y_coords);
cn_denorm->SetupNonLinear(&blob.denorm(), box, MAX_UINT8, MAX_UINT8,
0.0f, 0.0f, x_coords, y_coords);
} else {
cn_denorm->SetupNormalization(NULL, NULL, &blob.denorm(),
center.x(), center.y(),
51.2f / second_moments.x(),
51.2f / second_moments.y(),
128.0f, 128.0f);
}
}
// Helper normalizes the direction, assuming that it is at the given
// unnormed_pos, using the given denorm, starting at the root_denorm.
uinT8 NormalizeDirection(uinT8 dir, const FCOORD& unnormed_pos,
const DENORM& denorm, const DENORM* root_denorm) {
// Convert direction to a vector.
FCOORD unnormed_end;
unnormed_end.from_direction(dir);
unnormed_end += unnormed_pos;
FCOORD normed_pos, normed_end;
denorm.NormTransform(root_denorm, unnormed_pos, &normed_pos);
denorm.NormTransform(root_denorm, unnormed_end, &normed_end);
normed_end -= normed_pos;
return normed_end.to_direction();
}
// Helper returns the mean direction vector from the given stats. Use the
// mean direction from dirs if there is information available, otherwise, use
// the fit_vector from point_diffs.
static FCOORD MeanDirectionVector(const LLSQ& point_diffs, const LLSQ& dirs,
const FCOORD& start_pt,
const FCOORD& end_pt) {
FCOORD fit_vector;
if (dirs.count() > 0) {
// There were directions, so use them. To avoid wrap-around problems, we
// have 2 accumulators in dirs: x for normal directions and y for
// directions offset by 128. We will use the one with the least variance.
FCOORD mean_pt = dirs.mean_point();
double mean_dir = 0.0;
if (dirs.x_variance() <= dirs.y_variance()) {
mean_dir = mean_pt.x();
} else {
mean_dir = mean_pt.y() + 128;
}
fit_vector.from_direction(Modulo(IntCastRounded(mean_dir), 256));
} else {
// There were no directions, so we rely on the vector_fit to the points.
// Since the vector_fit is 180 degrees ambiguous, we align with the
// supplied feature_dir by making the scalar product non-negative.
FCOORD feature_dir(end_pt - start_pt);
fit_vector = point_diffs.vector_fit();
if (fit_vector.x() == 0.0f && fit_vector.y() == 0.0f) {
// There was only a single point. Use feature_dir directly.
fit_vector = feature_dir;
} else {
// Sometimes the least mean squares fit is wrong, due to the small sample
// of points and scaling. Use a 90 degree rotated vector if that matches
// feature_dir better.
FCOORD fit_vector2 = !fit_vector;
// The fit_vector is 180 degrees ambiguous, so resolve the ambiguity by
// insisting that the scalar product with the feature_dir should be +ve.
if (fit_vector % feature_dir < 0.0)
fit_vector = -fit_vector;
if (fit_vector2 % feature_dir < 0.0)
fit_vector2 = -fit_vector2;
// Even though fit_vector2 has a higher mean squared error, it might be
// a better fit, so use it if the dot product with feature_dir is bigger.
if (fit_vector2 % feature_dir > fit_vector % feature_dir)
fit_vector = fit_vector2;
}
}
return fit_vector;
}
// Helper computes one or more features corresponding to the given points.
// Emitted features are on the line defined by:
// start_pt + lambda * (end_pt - start_pt) for scalar lambda.
// Features are spaced at feature_length intervals.
static int ComputeFeatures(const FCOORD& start_pt, const FCOORD& end_pt,
double feature_length,
GenericVector<INT_FEATURE_STRUCT>* features) {
FCOORD feature_vector(end_pt - start_pt);
if (feature_vector.x() == 0.0f && feature_vector.y() == 0.0f) return 0;
// Compute theta for the feature based on its direction.
uinT8 theta = feature_vector.to_direction();
// Compute the number of features and lambda_step.
double target_length = feature_vector.length();
int num_features = IntCastRounded(target_length / feature_length);
if (num_features == 0) return 0;
// Divide the length evenly into num_features pieces.
double lambda_step = 1.0 / num_features;
double lambda = lambda_step / 2.0;
for (int f = 0; f < num_features; ++f, lambda += lambda_step) {
FCOORD feature_pt(start_pt);
feature_pt += feature_vector * lambda;
INT_FEATURE_STRUCT feature(feature_pt, theta);
features->push_back(feature);
}
return num_features;
}
// Gathers outline points and their directions from start_index into dirs by
// stepping along the outline and normalizing the coordinates until the
// required feature_length has been collected or end_index is reached.
// On input pos must point to the position corresponding to start_index and on
// return pos is updated to the current raw position, and pos_normed is set to
// the normed version of pos.
// Since directions wrap-around, they need special treatment to get the mean.
// Provided the cluster of directions doesn't straddle the wrap-around point,
// the simple mean works. If they do, then, unless the directions are wildly
// varying, the cluster rotated by 180 degrees will not straddle the wrap-
// around point, so mean(dir + 180 degrees) - 180 degrees will work. Since
// LLSQ conveniently stores the mean of 2 variables, we use it to store
// dir and dir+128 (128 is 180 degrees) and then use the resulting mean
// with the least variance.
static int GatherPoints(const C_OUTLINE* outline, double feature_length,
const DENORM& denorm, const DENORM* root_denorm,
int start_index, int end_index,
ICOORD* pos, FCOORD* pos_normed,
LLSQ* points, LLSQ* dirs) {
int step_length = outline->pathlength();
ICOORD step = outline->step(start_index % step_length);
// Prev_normed is the start point of this collection and will be set on the
// first iteration, and on later iterations used to determine the length
// that has been collected.
FCOORD prev_normed;
points->clear();
dirs->clear();
int num_points = 0;
int index;
for (index = start_index; index <= end_index; ++index, *pos += step) {
step = outline->step(index % step_length);
int edge_weight = outline->edge_strength_at_index(index % step_length);
if (edge_weight == 0) {
// This point has conflicting gradient and step direction, so ignore it.
continue;
}
// Get the sub-pixel precise location and normalize.
FCOORD f_pos = outline->sub_pixel_pos_at_index(*pos, index % step_length);
denorm.NormTransform(root_denorm, f_pos, pos_normed);
if (num_points == 0) {
// The start of this segment.
prev_normed = *pos_normed;
} else {
FCOORD offset = *pos_normed - prev_normed;
float length = offset.length();
if (length > feature_length) {
// We have gone far enough from the start. We will use this point in
// the next set so return what we have so far.
return index;
}
}
points->add(pos_normed->x(), pos_normed->y(), edge_weight);
int direction = outline->direction_at_index(index % step_length);
if (direction >= 0) {
direction = NormalizeDirection(direction, f_pos, denorm, root_denorm);
// Use both the direction and direction +128 so we are not trying to
// take the mean of something straddling the wrap-around point.
dirs->add(direction, Modulo(direction + 128, 256));
}
++num_points;
}
return index;
}
// Extracts Tesseract features and appends them to the features vector.
// Startpt to lastpt, inclusive, MUST have the same src_outline member,
// which may be NULL. The vector from lastpt to its next is included in
// the feature extraction. Hidden edges should be excluded by the caller.
// If force_poly is true, the features will be extracted from the polygonal
// approximation even if more accurate data is available.
static void ExtractFeaturesFromRun(
const EDGEPT* startpt, const EDGEPT* lastpt,
const DENORM& denorm, double feature_length, bool force_poly,
GenericVector<INT_FEATURE_STRUCT>* features) {
const EDGEPT* endpt = lastpt->next;
const C_OUTLINE* outline = startpt->src_outline;
if (outline != NULL && !force_poly) {
// Detailed information is available. We have to normalize only from
// the root_denorm to denorm.
const DENORM* root_denorm = denorm.RootDenorm();
int total_features = 0;
// Get the features from the outline.
int step_length = outline->pathlength();
int start_index = startpt->start_step;
// pos is the integer coordinates of the binary image steps.
ICOORD pos = outline->position_at_index(start_index);
// We use an end_index that allows us to use a positive increment, but that
// may be beyond the bounds of the outline steps/ due to wrap-around, to
// so we use % step_length everywhere, except for start_index.
int end_index = lastpt->start_step + lastpt->step_count;
if (end_index <= start_index)
end_index += step_length;
LLSQ prev_points;
LLSQ prev_dirs;
FCOORD prev_normed_pos = outline->sub_pixel_pos_at_index(pos, start_index);
denorm.NormTransform(root_denorm, prev_normed_pos, &prev_normed_pos);
LLSQ points;
LLSQ dirs;
FCOORD normed_pos;
int index = GatherPoints(outline, feature_length, denorm, root_denorm,
start_index, end_index, &pos, &normed_pos,
&points, &dirs);
while (index <= end_index) {
// At each iteration we nominally have 3 accumulated sets of points and
// dirs: prev_points/dirs, points/dirs, next_points/dirs and sum them
// into sum_points/dirs, but we don't necessarily get any features out,
// so if that is the case, we keep accumulating instead of rotating the
// accumulators.
LLSQ next_points;
LLSQ next_dirs;
FCOORD next_normed_pos;
index = GatherPoints(outline, feature_length, denorm, root_denorm,
index, end_index, &pos, &next_normed_pos,
&next_points, &next_dirs);
LLSQ sum_points(prev_points);
// TODO(rays) find out why it is better to use just dirs and next_dirs
// in sum_dirs, instead of using prev_dirs as well.
LLSQ sum_dirs(dirs);
sum_points.add(points);
sum_points.add(next_points);
sum_dirs.add(next_dirs);
bool made_features = false;
// If we have some points, we can try making some features.
if (sum_points.count() > 0) {
// We have gone far enough from the start. Make a feature and restart.
FCOORD fit_pt = sum_points.mean_point();
FCOORD fit_vector = MeanDirectionVector(sum_points, sum_dirs,
prev_normed_pos, normed_pos);
// The segment to which we fit features is the line passing through
// fit_pt in direction of fit_vector that starts nearest to
// prev_normed_pos and ends nearest to normed_pos.
FCOORD start_pos = prev_normed_pos.nearest_pt_on_line(fit_pt,
fit_vector);
FCOORD end_pos = normed_pos.nearest_pt_on_line(fit_pt, fit_vector);
// Possible correction to match the adjacent polygon segment.
if (total_features == 0 && startpt != endpt) {
FCOORD poly_pos(startpt->pos.x, startpt->pos.y);
denorm.LocalNormTransform(poly_pos, &start_pos);
}
if (index > end_index && startpt != endpt) {
FCOORD poly_pos(endpt->pos.x, endpt->pos.y);
denorm.LocalNormTransform(poly_pos, &end_pos);
}
int num_features = ComputeFeatures(start_pos, end_pos, feature_length,
features);
if (num_features > 0) {
// We made some features so shuffle the accumulators.
prev_points = points;
prev_dirs = dirs;
prev_normed_pos = normed_pos;
points = next_points;
dirs = next_dirs;
made_features = true;
total_features += num_features;
}
// The end of the next set becomes the end next time around.
normed_pos = next_normed_pos;
}
if (!made_features) {
// We didn't make any features, so keep the prev accumulators and
// add the next ones into the current.
points.add(next_points);
dirs.add(next_dirs);
}
}
} else {
// There is no outline, so we are forced to use the polygonal approximation.
const EDGEPT* pt = startpt;
do {
FCOORD start_pos(pt->pos.x, pt->pos.y);
FCOORD end_pos(pt->next->pos.x, pt->next->pos.y);
denorm.LocalNormTransform(start_pos, &start_pos);
denorm.LocalNormTransform(end_pos, &end_pos);
ComputeFeatures(start_pos, end_pos, feature_length, features);
} while ((pt = pt->next) != endpt);
}
}
// Extracts sets of 3-D features of length kStandardFeatureLength (=12.8), as
// (x,y) position and angle as measured counterclockwise from the vector
// <-1, 0>, from blob using two normalizations defined by bl_denorm and
// cn_denorm. See SetpuBLCNDenorms for definitions.
// If outline_cn_counts is not NULL, on return it contains the cumulative
// number of cn features generated for each outline in the blob (in order).
// Thus after the first outline, there were (*outline_cn_counts)[0] features,
// after the second outline, there were (*outline_cn_counts)[1] features etc.
void Classify::ExtractFeatures(const TBLOB& blob,
bool nonlinear_norm,
GenericVector<INT_FEATURE_STRUCT>* bl_features,
GenericVector<INT_FEATURE_STRUCT>* cn_features,
INT_FX_RESULT_STRUCT* results,
GenericVector<int>* outline_cn_counts) {
DENORM bl_denorm, cn_denorm;
tesseract::Classify::SetupBLCNDenorms(blob, nonlinear_norm,
&bl_denorm, &cn_denorm, results);
if (outline_cn_counts != NULL)
outline_cn_counts->truncate(0);
// Iterate the outlines.
for (TESSLINE* ol = blob.outlines; ol != NULL; ol = ol->next) {
// Iterate the polygon.
EDGEPT* loop_pt = ol->FindBestStartPt();
EDGEPT* pt = loop_pt;
if (pt == NULL) continue;
do {
if (pt->IsHidden()) continue;
// Find a run of equal src_outline.
EDGEPT* last_pt = pt;
do {
last_pt = last_pt->next;
} while (last_pt != loop_pt && !last_pt->IsHidden() &&
last_pt->src_outline == pt->src_outline);
last_pt = last_pt->prev;
// Until the adaptive classifier can be weaned off polygon segments,
// we have to force extraction from the polygon for the bl_features.
ExtractFeaturesFromRun(pt, last_pt, bl_denorm, kStandardFeatureLength,
true, bl_features);
ExtractFeaturesFromRun(pt, last_pt, cn_denorm, kStandardFeatureLength,
false, cn_features);
pt = last_pt;
} while ((pt = pt->next) != loop_pt);
if (outline_cn_counts != NULL)
outline_cn_counts->push_back(cn_features->size());
}
results->NumBL = bl_features->size();
results->NumCN = cn_features->size();
results->YBottom = blob.bounding_box().bottom();
results->YTop = blob.bounding_box().top();
results->Width = blob.bounding_box().width();
}
} // namespace tesseract
/*--------------------------------------------------------------------------*/
// Extract a set of standard-sized features from Blobs and write them out in
// two formats: baseline normalized and character normalized.
//
// We presume the Blobs are already scaled so that x-height=128 units
//
// Standard Features:
// We take all outline segments longer than 7 units and chop them into
// standard-sized segments of approximately 13 = (64 / 5) units.
// When writing these features out, we output their center and angle as
// measured counterclockwise from the vector <-1, 0>
//
// Baseline Normalized Output:
// We center the grapheme by aligning the x-coordinate of its centroid with
// x=0 and subtracting 128 from the y-coordinate.
//
// Character Normalized Output:
// We align the grapheme's centroid at the origin and scale it asymmetrically
// in x and y so that the result is vaguely square.
//
// Deprecated! Prefer tesseract::Classify::ExtractFeatures instead.
bool ExtractIntFeat(const TBLOB& blob,
bool nonlinear_norm,
INT_FEATURE_ARRAY baseline_features,
INT_FEATURE_ARRAY charnorm_features,
INT_FX_RESULT_STRUCT* results) {
GenericVector<INT_FEATURE_STRUCT> bl_features;
GenericVector<INT_FEATURE_STRUCT> cn_features;
tesseract::Classify::ExtractFeatures(blob, nonlinear_norm,
&bl_features, &cn_features, results,
NULL);
if (bl_features.size() == 0 || cn_features.size() == 0 ||
bl_features.size() > MAX_NUM_INT_FEATURES ||
cn_features.size() > MAX_NUM_INT_FEATURES) {
return false; // Feature extraction failed.
}
memcpy(baseline_features, &bl_features[0],
bl_features.size() * sizeof(bl_features[0]));
memcpy(charnorm_features, &cn_features[0],
cn_features.size() * sizeof(cn_features[0]));
return true;
}
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