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tesseract/textord/alignedblob.cpp

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///////////////////////////////////////////////////////////////////////
// File: alignedblob.cpp
// Description: Subclass of BBGrid to find vertically aligned blobs.
// Author: Ray Smith
// Created: Fri Mar 21 15:03:01 PST 2008
//
// (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.
//
///////////////////////////////////////////////////////////////////////
#ifdef HAVE_CONFIG_H
#include "config_auto.h"
#endif
#include "alignedblob.h"
#include "ndminx.h"
INT_VAR(textord_debug_tabfind, 0, "Debug tab finding");
INT_VAR(textord_debug_bugs, 0, "Turn on output related to bugs in tab finding");
INT_VAR(textord_testregion_left, -1, "Left edge of debug reporting rectangle");
INT_VAR(textord_testregion_top, -1, "Top edge of debug reporting rectangle");
INT_VAR(textord_testregion_right, MAX_INT32, "Right edge of debug rectangle");
INT_VAR(textord_testregion_bottom, MAX_INT32, "Bottom edge of debug rectangle");
BOOL_VAR(textord_debug_images, false, "Use greyed image background for debug");
BOOL_VAR(textord_debug_printable, false, "Make debug windows printable");
namespace tesseract {
// Fraction of resolution used as alignment tolerance for aligned tabs.
const double kAlignedFraction = 0.03125;
// Fraction of resolution used as alignment tolerance for ragged tabs.
const double kRaggedFraction = 2.5;
// Fraction of height used as a minimum gutter gap for aligned blobs.
const double kAlignedGapFraction = 0.75;
// Fraction of height used as a minimum gutter gap for ragged tabs.
const double kRaggedGapFraction = 1.0;
// Constant number of pixels used as alignment tolerance for line finding.
const int kVLineAlignment = 3;
// Constant number of pixels used as gutter gap tolerance for line finding.
const int kVLineGutter = 1;
// Constant number of pixels used as the search size for line finding.
const int kVLineSearchSize = 150;
// Min number of points to accept for a ragged tab stop.
const int kMinRaggedTabs = 5;
// Min number of points to accept for an aligned tab stop.
const int kMinAlignedTabs = 4;
// Constant number of pixels minimum height of a vertical line.
const int kVLineMinLength = 500;
// Minimum gradient for a vertical tab vector. Used to prune away junk
// tab vectors with what would be a ridiculously large skew angle.
// Value corresponds to tan(90 - max allowed skew angle)
const double kMinTabGradient = 4.0;
// Tolerance to skew on top of current estimate of skew. Divide x or y length
// by kMaxSkewFactor to get the y or x skew distance.
// If the angle is small, the angle in degrees is roughly 60/kMaxSkewFactor.
const int kMaxSkewFactor = 15;
// Constant part of textord_debug_pix_.
const char* kTextordDebugPix = "psdebug_pix";
// Name of image file to use if textord_debug_images is true.
STRING AlignedBlob::textord_debug_pix_ = kTextordDebugPix;
// Index to image file to use if textord_debug_images is true.
int AlignedBlob::debug_pix_index_ = 0;
// Increment the serial number counter and set the string to use
// for a filename if textord_debug_images is true.
void AlignedBlob::IncrementDebugPix() {
++debug_pix_index_;
textord_debug_pix_ = kTextordDebugPix;
char numbuf[32];
snprintf(numbuf, sizeof(numbuf), "%d", debug_pix_index_);
textord_debug_pix_ += numbuf;
textord_debug_pix_ += ".pix";
}
// Constructor to set the parameters for finding aligned and ragged tabs.
// Vertical_x and vertical_y are the current estimates of the true vertical
// direction (up) in the image. Height is the height of the starter blob.
// v_gap_multiple is the multiple of height that will be used as a limit
// on vertical gap before giving up and calling the line ended.
// resolution is the original image resolution, and align0 indicates the
// type of tab stop to be found.
AlignedBlobParams::AlignedBlobParams(int vertical_x, int vertical_y,
int height, int v_gap_multiple,
int min_gutter_width,
int resolution, TabAlignment align0)
: right_tab(align0 == TA_RIGHT_RAGGED || align0 == TA_RIGHT_ALIGNED),
ragged(align0 == TA_LEFT_RAGGED || align0 == TA_RIGHT_RAGGED),
alignment(align0),
confirmed_type(TT_CONFIRMED),
min_length(0) {
// Set the tolerances according to the type of line sought.
// For tab search, these are based on the image resolution for most, or
// the height of the starting blob for the maximum vertical gap.
max_v_gap = height * v_gap_multiple;
if (ragged) {
// In the case of a ragged edge, we are much more generous with the
// inside alignment fraction, but also require a much bigger gutter.
gutter_fraction = kRaggedGapFraction;
if (alignment == TA_RIGHT_RAGGED) {
l_align_tolerance = static_cast<int>(resolution * kRaggedFraction + 0.5);
r_align_tolerance = static_cast<int>(resolution * kAlignedFraction + 0.5);
} else {
l_align_tolerance = static_cast<int>(resolution * kAlignedFraction + 0.5);
r_align_tolerance = static_cast<int>(resolution * kRaggedFraction + 0.5);
}
min_points = kMinRaggedTabs;
} else {
gutter_fraction = kAlignedGapFraction;
l_align_tolerance = static_cast<int>(resolution * kAlignedFraction + 0.5);
r_align_tolerance = static_cast<int>(resolution * kAlignedFraction + 0.5);
min_points = kMinAlignedTabs;
}
min_gutter = static_cast<int>(height * gutter_fraction + 0.5);
if (min_gutter < min_gutter_width)
min_gutter = min_gutter_width;
// Fit the vertical vector into an ICOORD, which is 16 bit.
set_vertical(vertical_x, vertical_y);
}
// Constructor to set the parameters for finding vertical lines.
// Vertical_x and vertical_y are the current estimates of the true vertical
// direction (up) in the image. Width is the width of the starter blob.
AlignedBlobParams::AlignedBlobParams(int vertical_x, int vertical_y,
int width)
: gutter_fraction(0.0),
right_tab(false),
ragged(false),
alignment(TA_SEPARATOR),
confirmed_type(TT_VLINE),
max_v_gap(kVLineSearchSize),
min_gutter(kVLineGutter),
min_points(1),
min_length(kVLineMinLength) {
// Compute threshold for left and right alignment.
l_align_tolerance = MAX(kVLineAlignment, width);
r_align_tolerance = MAX(kVLineAlignment, width);
// Fit the vertical vector into an ICOORD, which is 16 bit.
set_vertical(vertical_x, vertical_y);
}
// Fit the vertical vector into an ICOORD, which is 16 bit.
void AlignedBlobParams::set_vertical(int vertical_x, int vertical_y) {
int factor = 1;
if (vertical_y > MAX_INT16)
factor = vertical_y / MAX_INT16 + 1;
vertical.set_x(vertical_x / factor);
vertical.set_y(vertical_y / factor);
}
AlignedBlob::AlignedBlob(int gridsize,
const ICOORD& bleft, const ICOORD& tright)
: BlobGrid(gridsize, bleft, tright) {
}
AlignedBlob::~AlignedBlob() {
}
// Return true if the given coordinates are within the test rectangle
// and the debug level is at least the given detail level.
bool AlignedBlob::WithinTestRegion(int detail_level, int x, int y) {
if (textord_debug_tabfind < detail_level)
return false;
return x >= textord_testregion_left && x <= textord_testregion_right &&
y <= textord_testregion_top && y >= textord_testregion_bottom;
}
// Display the tab codes of the BLOBNBOXes in this grid.
ScrollView* AlignedBlob::DisplayTabs(const char* window_name,
ScrollView* tab_win) {
#ifndef GRAPHICS_DISABLED
if (tab_win == NULL)
tab_win = MakeWindow(0, 50, window_name);
// For every tab in the grid, display it.
GridSearch<BLOBNBOX, BLOBNBOX_CLIST, BLOBNBOX_C_IT> gsearch(this);
gsearch.StartFullSearch();
BLOBNBOX* bbox;
while ((bbox = gsearch.NextFullSearch()) != NULL) {
const TBOX& box = bbox->bounding_box();
int left_x = box.left();
int right_x = box.right();
int top_y = box.top();
int bottom_y = box.bottom();
TabType tabtype = bbox->left_tab_type();
if (tabtype != TT_NONE) {
if (tabtype == TT_MAYBE_ALIGNED)
tab_win->Pen(ScrollView::BLUE);
else if (tabtype == TT_MAYBE_RAGGED)
tab_win->Pen(ScrollView::YELLOW);
else if (tabtype == TT_CONFIRMED)
tab_win->Pen(ScrollView::GREEN);
else
tab_win->Pen(ScrollView::GREY);
tab_win->Line(left_x, top_y, left_x, bottom_y);
}
tabtype = bbox->right_tab_type();
if (tabtype != TT_NONE) {
if (tabtype == TT_MAYBE_ALIGNED)
tab_win->Pen(ScrollView::MAGENTA);
else if (tabtype == TT_MAYBE_RAGGED)
tab_win->Pen(ScrollView::ORANGE);
else if (tabtype == TT_CONFIRMED)
tab_win->Pen(ScrollView::RED);
else
tab_win->Pen(ScrollView::GREY);
tab_win->Line(right_x, top_y, right_x, bottom_y);
}
}
tab_win->Update();
#endif
return tab_win;
}
// Helper returns true if the total number of line_crossings of all the blobs
// in the list is at least 2.
static bool AtLeast2LineCrossings(BLOBNBOX_CLIST* blobs) {
BLOBNBOX_C_IT it(blobs);
int total_crossings = 0;
for (it.mark_cycle_pt(); !it.cycled_list(); it.forward()) {
total_crossings += it.data()->line_crossings();
}
return total_crossings >= 2;
}
// Finds a vector corresponding to a set of vertically aligned blob edges
// running through the given box. The type of vector returned and the
// search parameters are determined by the AlignedBlobParams.
// vertical_x and y are updated with an estimate of the real
// vertical direction. (skew finding.)
// Returns NULL if no decent vector can be found.
TabVector* AlignedBlob::FindVerticalAlignment(AlignedBlobParams align_params,
BLOBNBOX* bbox,
int* vertical_x,
int* vertical_y) {
int ext_start_y, ext_end_y;
BLOBNBOX_CLIST good_points;
// Search up and then down from the starting bbox.
TBOX box = bbox->bounding_box();
bool debug = WithinTestRegion(2, box.left(), box.bottom());
int pt_count = AlignTabs(align_params, false, bbox, &good_points, &ext_end_y);
pt_count += AlignTabs(align_params, true, bbox, &good_points, &ext_start_y);
BLOBNBOX_C_IT it(&good_points);
it.move_to_last();
box = it.data()->bounding_box();
int end_y = box.top();
int end_x = align_params.right_tab ? box.right() : box.left();
it.move_to_first();
box = it.data()->bounding_box();
int start_x = align_params.right_tab ? box.right() : box.left();
int start_y = box.bottom();
// Acceptable tab vectors must have a mininum number of points,
// have a minimum acceptable length, and have a minimum gradient.
// The gradient corresponds to the skew angle.
// Ragged tabs don't need to satisfy the gradient condition, as they
// will always end up parallel to the vertical direction.
bool at_least_2_crossings = AtLeast2LineCrossings(&good_points);
if ((pt_count >= align_params.min_points &&
end_y - start_y >= align_params.min_length &&
(align_params.ragged ||
end_y - start_y >= abs(end_x - start_x) * kMinTabGradient)) ||
at_least_2_crossings) {
int confirmed_points = 0;
// Count existing confirmed points to see if vector is acceptable.
for (it.mark_cycle_pt(); !it.cycled_list(); it.forward()) {
bbox = it.data();
if (align_params.right_tab) {
if (bbox->right_tab_type() == align_params.confirmed_type)
++confirmed_points;
} else {
if (bbox->left_tab_type() == align_params.confirmed_type)
++confirmed_points;
}
}
// Ragged vectors are not allowed to use too many already used points.
if (!align_params.ragged ||
confirmed_points + confirmed_points < pt_count) {
const TBOX& box = bbox->bounding_box();
if (debug) {
tprintf("Confirming tab vector of %d pts starting at %d,%d\n",
pt_count, box.left(), box.bottom());
}
// Flag all the aligned neighbours as confirmed .
for (it.mark_cycle_pt(); !it.cycled_list(); it.forward()) {
bbox = it.data();
if (align_params.right_tab) {
bbox->set_right_tab_type(align_params.confirmed_type);
} else {
bbox->set_left_tab_type(align_params.confirmed_type);
}
if (debug) {
bbox->bounding_box().print();
}
}
// Now make the vector and return it.
TabVector* result = TabVector::FitVector(align_params.alignment,
align_params.vertical,
ext_start_y, ext_end_y,
&good_points,
vertical_x, vertical_y);
result->set_intersects_other_lines(at_least_2_crossings);
if (debug) {
tprintf("Box was %d, %d\n", box.left(), box.bottom());
result->Print("After fitting");
}
return result;
} else if (debug) {
tprintf("Ragged tab used too many used points: %d out of %d\n",
confirmed_points, pt_count);
}
} else if (debug) {
tprintf("Tab vector failed basic tests: pt count %d vs min %d, "
"length %d vs min %d, min grad %g\n",
pt_count, align_params.min_points, end_y - start_y,
align_params.min_length, abs(end_x - start_x) * kMinTabGradient);
}
return NULL;
}
// Find a set of blobs that are aligned in the given vertical
// direction with the given blob. Returns a list of aligned
// blobs and the number in the list.
// For other parameters see FindAlignedBlob below.
int AlignedBlob::AlignTabs(const AlignedBlobParams& params,
bool top_to_bottom, BLOBNBOX* bbox,
BLOBNBOX_CLIST* good_points, int* end_y) {
int ptcount = 0;
BLOBNBOX_C_IT it(good_points);
TBOX box = bbox->bounding_box();
bool debug = WithinTestRegion(2, box.left(), box.bottom());
if (debug) {
tprintf("Starting alignment run at blob:");
box.print();
}
int x_start = params.right_tab ? box.right() : box.left();
while (bbox != NULL) {
// Add the blob to the list if the appropriate side is a tab candidate,
// or if we are working on a ragged tab.
TabType type = params.right_tab ? bbox->right_tab_type()
: bbox->left_tab_type();
if (((type != TT_NONE && type != TT_MAYBE_RAGGED) || params.ragged) &&
(it.empty() || it.data() != bbox)) {
if (top_to_bottom)
it.add_before_then_move(bbox);
else
it.add_after_then_move(bbox);
++ptcount;
}
// Find the next blob that is aligned with the current one.
// FindAlignedBlob guarantees that forward progress will be made in the
// top_to_bottom direction, and therefore eventually it will return NULL,
// making this while (bbox != NULL) loop safe.
bbox = FindAlignedBlob(params, top_to_bottom, bbox, x_start, end_y);
if (bbox != NULL) {
box = bbox->bounding_box();
if (!params.ragged)
x_start = params.right_tab ? box.right() : box.left();
}
}
if (debug) {
tprintf("Alignment run ended with %d pts at blob:", ptcount);
box.print();
}
return ptcount;
}
// Search vertically for a blob that is aligned with the input bbox.
// The search parameters are determined by AlignedBlobParams.
// top_to_bottom tells whether to search down or up.
// The return value is NULL if nothing was found in the search box
// or if a blob was found in the gutter. On a NULL return, end_y
// is set to the edge of the search box or the leading edge of the
// gutter blob if one was found.
BLOBNBOX* AlignedBlob::FindAlignedBlob(const AlignedBlobParams& p,
bool top_to_bottom, BLOBNBOX* bbox,
int x_start, int* end_y) {
TBOX box = bbox->bounding_box();
// If there are separator lines, get the column edges.
int left_column_edge = bbox->left_rule();
int right_column_edge = bbox->right_rule();
// start_y is used to guarantee that forward progress is made and the
// search does not go into an infinite loop. New blobs must extend the
// line beyond start_y.
int start_y = top_to_bottom ? box.bottom() : box.top();
if (WithinTestRegion(2, x_start, start_y)) {
tprintf("Column edges for blob at (%d,%d)->(%d,%d) are [%d, %d]\n",
box.left(), box.top(), box.right(), box.bottom(),
left_column_edge, right_column_edge);
}
// Compute skew tolerance.
int skew_tolerance = p.max_v_gap / kMaxSkewFactor;
// Calculate xmin and xmax of the search box so that it contains
// all possibly relevant boxes up to p.max_v_gap above or below accoording
// to top_to_bottom.
// Start with a notion of vertical with the current estimate.
int x2 = (p.max_v_gap * p.vertical.x() + p.vertical.y()/2) / p.vertical.y();
if (top_to_bottom) {
x2 = x_start - x2;
*end_y = start_y - p.max_v_gap;
} else {
x2 = x_start + x2;
*end_y = start_y + p.max_v_gap;
}
// Expand the box by an additional skew tolerance
int xmin = MIN(x_start, x2) - skew_tolerance;
int xmax = MAX(x_start, x2) + skew_tolerance;
// Now add direction-specific tolerances.
if (p.right_tab) {
xmax += p.min_gutter;
xmin -= p.l_align_tolerance;
} else {
xmax += p.r_align_tolerance;
xmin -= p.min_gutter;
}
// Setup a vertical search for an aligned blob.
GridSearch<BLOBNBOX, BLOBNBOX_CLIST, BLOBNBOX_C_IT> vsearch(this);
if (WithinTestRegion(2, x_start, start_y))
tprintf("Starting %s %s search at %d-%d,%d, search_size=%d, gutter=%d\n",
p.ragged ? "Ragged" : "Aligned", p.right_tab ? "Right" : "Left",
xmin, xmax, start_y, p.max_v_gap, p.min_gutter);
vsearch.StartVerticalSearch(xmin, xmax, start_y);
// result stores the best real return value.
BLOBNBOX* result = NULL;
// The backup_result is not a tab candidate and can be used if no
// real tab candidate result is found.
BLOBNBOX* backup_result = NULL;
// neighbour is the blob that is currently being investigated.
BLOBNBOX* neighbour = NULL;
while ((neighbour = vsearch.NextVerticalSearch(top_to_bottom)) != NULL) {
if (neighbour == bbox)
continue;
TBOX nbox = neighbour->bounding_box();
int n_y = (nbox.top() + nbox.bottom()) / 2;
if ((!top_to_bottom && n_y > start_y + p.max_v_gap) ||
(top_to_bottom && n_y < start_y - p.max_v_gap)) {
if (WithinTestRegion(2, x_start, start_y))
tprintf("Neighbour too far at (%d,%d)->(%d,%d)\n",
nbox.left(), nbox.bottom(), nbox.right(), nbox.top());
break; // Gone far enough.
}
// It is CRITICAL to ensure that forward progress is made, (strictly
// in/decreasing n_y) or the caller could loop infinitely, while
// waiting for a sequence of blobs in a line to end.
// NextVerticalSearch alone does not guarantee this, as there may be
// more than one blob in a grid cell. See comment in AlignTabs.
if ((n_y < start_y) != top_to_bottom || nbox.y_overlap(box))
continue; // Only look in the required direction.
if (result != NULL && result->bounding_box().y_gap(nbox) > gridsize())
return result; // This result is clear.
if (backup_result != NULL && p.ragged && result == NULL &&
backup_result->bounding_box().y_gap(nbox) > gridsize())
return backup_result; // This result is clear.
// If the neighbouring blob is the wrong side of a separator line, then it
// "doesn't exist" as far as we are concerned.
int x_at_n_y = x_start + (n_y - start_y) * p.vertical.x() / p.vertical.y();
if (x_at_n_y < neighbour->left_crossing_rule() ||
x_at_n_y > neighbour->right_crossing_rule())
continue; // Separator line in the way.
int n_left = nbox.left();
int n_right = nbox.right();
int n_x = p.right_tab ? n_right : n_left;
if (WithinTestRegion(2, x_start, start_y))
tprintf("neighbour at (%d,%d)->(%d,%d), n_x=%d, n_y=%d, xatn=%d\n",
nbox.left(), nbox.bottom(), nbox.right(), nbox.top(),
n_x, n_y, x_at_n_y);
if (p.right_tab &&
n_left < x_at_n_y + p.min_gutter &&
n_right > x_at_n_y + p.r_align_tolerance &&
(p.ragged || n_left < x_at_n_y + p.gutter_fraction * nbox.height())) {
// In the gutter so end of line.
if (bbox->right_tab_type() >= TT_MAYBE_ALIGNED)
bbox->set_right_tab_type(TT_DELETED);
*end_y = top_to_bottom ? nbox.top() : nbox.bottom();
if (WithinTestRegion(2, x_start, start_y))
tprintf("gutter\n");
return NULL;
}
if (!p.right_tab &&
n_left < x_at_n_y - p.l_align_tolerance &&
n_right > x_at_n_y - p.min_gutter &&
(p.ragged || n_right > x_at_n_y - p.gutter_fraction * nbox.height())) {
// In the gutter so end of line.
if (bbox->left_tab_type() >= TT_MAYBE_ALIGNED)
bbox->set_left_tab_type(TT_DELETED);
*end_y = top_to_bottom ? nbox.top() : nbox.bottom();
if (WithinTestRegion(2, x_start, start_y))
tprintf("gutter\n");
return NULL;
}
if ((p.right_tab && neighbour->leader_on_right()) ||
(!p.right_tab && neighbour->leader_on_left()))
continue; // Neighbours of leaders are not allowed to be used.
if (n_x <= x_at_n_y + p.r_align_tolerance &&
n_x >= x_at_n_y - p.l_align_tolerance) {
// Aligned so keep it. If it is a marked tab save it as result,
// otherwise keep it as backup_result to return in case of later failure.
if (WithinTestRegion(2, x_start, start_y))
tprintf("aligned, seeking%d, l=%d, r=%d\n",
p.right_tab, neighbour->left_tab_type(),
neighbour->right_tab_type());
TabType n_type = p.right_tab ? neighbour->right_tab_type()
: neighbour->left_tab_type();
if (n_type != TT_NONE && (p.ragged || n_type != TT_MAYBE_RAGGED)) {
if (result == NULL) {
result = neighbour;
} else {
// Keep the closest neighbour by Euclidean distance.
// This prevents it from picking a tab blob in another column.
const TBOX& old_box = result->bounding_box();
int x_diff = p.right_tab ? old_box.right() : old_box.left();
x_diff -= x_at_n_y;
int y_diff = (old_box.top() + old_box.bottom()) / 2 - start_y;
int old_dist = x_diff * x_diff + y_diff * y_diff;
x_diff = n_x - x_at_n_y;
y_diff = n_y - start_y;
int new_dist = x_diff * x_diff + y_diff * y_diff;
if (new_dist < old_dist)
result = neighbour;
}
} else if (backup_result == NULL) {
if (WithinTestRegion(2, x_start, start_y))
tprintf("Backup\n");
backup_result = neighbour;
} else {
TBOX backup_box = backup_result->bounding_box();
if ((p.right_tab && backup_box.right() < nbox.right()) ||
(!p.right_tab && backup_box.left() > nbox.left())) {
if (WithinTestRegion(2, x_start, start_y))
tprintf("Better backup\n");
backup_result = neighbour;
}
}
}
}
return result != NULL ? result : backup_result;
}
} // namespace tesseract.
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