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tesseract/textord/linefind.cpp
zdenop 9cf08ca8d3 fix build with -DGRAPHICS_DISABLED 
git-svn-id: https://tesseract-ocr.googlecode.com/svn/trunk@981 d0cd1f9f-072b-0410-8dd7-cf729c803f20
2014-01-11 23:08:54 +00:00

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///////////////////////////////////////////////////////////////////////
// File: linefind.cpp
// Description: Class to find vertical lines in an image and create
// a corresponding list of empty blobs.
// Author: Ray Smith
// Created: Thu Mar 20 09:49:01 PDT 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 _MSC_VER
#pragma warning(disable:4244) // Conversion warnings
#endif
#ifdef HAVE_CONFIG_H
#include "config_auto.h"
#endif
#include "linefind.h"
#include "alignedblob.h"
#include "tabvector.h"
#include "blobbox.h"
#include "edgblob.h"
#include "openclwrapper.h"
#include "allheaders.h"
namespace tesseract {
/// Denominator of resolution makes max pixel width to allow thin lines.
const int kThinLineFraction = 20;
/// Denominator of resolution makes min pixels to demand line lengths to be.
const int kMinLineLengthFraction = 4;
/// Spacing of cracks across the page to break up tall vertical lines.
const int kCrackSpacing = 100;
/// Grid size used by line finder. Not very critical.
const int kLineFindGridSize = 50;
// Min width of a line in pixels to be considered thick.
const int kMinThickLineWidth = 12;
// Max size of line residue. (The pixels that fail the long thin opening, and
// therefore don't make it to the candidate line mask, but are nevertheless
// part of the line.)
const int kMaxLineResidue = 6;
// Min length in inches of a line segment that exceeds kMinThickLineWidth in
// thickness. (Such lines shouldn't break by simple image degradation.)
const double kThickLengthMultiple = 0.75;
// Max fraction of line box area that can be occupied by non-line pixels.
const double kMaxNonLineDensity = 0.25;
// Max height of a music stave in inches.
const double kMaxStaveHeight = 1.0;
// Minimum fraction of pixels in a music rectangle connected to the staves.
const double kMinMusicPixelFraction = 0.75;
// Erases the unused blobs from the line_pix image, taking into account
// whether this was a horizontal or vertical line set.
static void RemoveUnusedLineSegments(bool horizontal_lines,
BLOBNBOX_LIST* line_bblobs,
Pix* line_pix) {
int height = pixGetHeight(line_pix);
BLOBNBOX_IT bbox_it(line_bblobs);
for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
BLOBNBOX* blob = bbox_it.data();
if (blob->left_tab_type() != TT_VLINE) {
const TBOX& box = blob->bounding_box();
Box* pixbox = NULL;
if (horizontal_lines) {
// Horizontal lines are in tess format and also have x and y flipped
// (to use FindVerticalAlignment) so we have to flip x and y and then
// convert to Leptonica by height - flipped x (ie the right edge).
// See GetLineBoxes for more explanation.
pixbox = boxCreate(box.bottom(), height - box.right(),
box.height(), box.width());
} else {
// For vertical lines, just flip upside-down to convert to Leptonica.
// The y position of the box in Leptonica terms is the distance from
// the top of the image to the top of the box.
pixbox = boxCreate(box.left(), height - box.top(),
box.width(), box.height());
}
pixClearInRect(line_pix, pixbox);
boxDestroy(&pixbox);
}
}
}
// Helper subtracts the line_pix image from the src_pix, and removes residue
// as well by removing components that touch the line, but are not in the
// non_line_pix mask. It is assumed that the non_line_pix mask has already
// been prepared to required accuracy.
static void SubtractLinesAndResidue(Pix* line_pix, Pix* non_line_pix,
int resolution, Pix* src_pix) {
// First remove the lines themselves.
pixSubtract(src_pix, src_pix, line_pix);
// Subtract the non-lines from the image to get the residue.
Pix* residue_pix = pixSubtract(NULL, src_pix, non_line_pix);
// Dilate the lines so they touch the residue.
Pix* fat_line_pix = pixDilateBrick(NULL, line_pix, 3, 3);
// Seed fill the fat lines to get all the residue.
pixSeedfillBinary(fat_line_pix, fat_line_pix, residue_pix, 8);
// Subtract the residue from the original image.
pixSubtract(src_pix, src_pix, fat_line_pix);
pixDestroy(&fat_line_pix);
pixDestroy(&residue_pix);
}
// Returns the maximum strokewidth in the given binary image by doubling
// the maximum of the distance function.
static int MaxStrokeWidth(Pix* pix) {
Pix* dist_pix = pixDistanceFunction(pix, 4, 8, L_BOUNDARY_BG);
int width = pixGetWidth(dist_pix);
int height = pixGetHeight(dist_pix);
int wpl = pixGetWpl(dist_pix);
l_uint32* data = pixGetData(dist_pix);
// Find the maximum value in the distance image.
int max_dist = 0;
for (int y = 0; y < height; ++y) {
for (int x = 0; x < width; ++x) {
int pixel = GET_DATA_BYTE(data, x);
if (pixel > max_dist)
max_dist = pixel;
}
data += wpl;
}
pixDestroy(&dist_pix);
return max_dist * 2;
}
// Returns the number of components in the intersection_pix touched by line_box.
static int NumTouchingIntersections(Box* line_box, Pix* intersection_pix) {
if (intersection_pix == NULL) return 0;
Pix* rect_pix = pixClipRectangle(intersection_pix, line_box, NULL);
Boxa* boxa = pixConnComp(rect_pix, NULL, 8);
pixDestroy(&rect_pix);
if (boxa == NULL) return false;
int result = boxaGetCount(boxa);
boxaDestroy(&boxa);
return result;
}
// Returns the number of black pixels found in the box made by adding the line
// width to both sides of the line bounding box. (Increasing the smallest
// dimension of the bounding box.)
static int CountPixelsAdjacentToLine(int line_width, Box* line_box,
Pix* nonline_pix) {
l_int32 x, y, box_width, box_height;
boxGetGeometry(line_box, &x, &y, &box_width, &box_height);
if (box_width > box_height) {
// horizontal line.
int bottom = MIN(pixGetHeight(nonline_pix), y + box_height + line_width);
y = MAX(0, y - line_width);
box_height = bottom - y;
} else {
// Vertical line.
int right = MIN(pixGetWidth(nonline_pix), x + box_width + line_width);
x = MAX(0, x - line_width);
box_width = right - x;
}
Box* box = boxCreate(x, y, box_width, box_height);
Pix* rect_pix = pixClipRectangle(nonline_pix, box, NULL);
boxDestroy(&box);
l_int32 result;
pixCountPixels(rect_pix, &result, NULL);
pixDestroy(&rect_pix);
return result;
}
// Helper erases false-positive line segments from the input/output line_pix.
// 1. Since thick lines shouldn't really break up, we can eliminate some false
// positives by marking segments that are at least kMinThickLineWidth
// thickness, yet have a length less than min_thick_length.
// 2. Lines that don't have at least 2 intersections with other lines and have
// a lot of neighbouring non-lines are probably not lines (perhaps arabic
// or Hindi words, or underlines.)
// Bad line components are erased from line_pix.
// Returns the number of remaining connected components.
static int FilterFalsePositives(int resolution, Pix* nonline_pix,
Pix* intersection_pix, Pix* line_pix) {
int min_thick_length = static_cast<int>(resolution * kThickLengthMultiple);
Pixa* pixa = NULL;
Boxa* boxa = pixConnComp(line_pix, &pixa, 8);
// Iterate over the boxes to remove false positives.
int nboxes = boxaGetCount(boxa);
int remaining_boxes = nboxes;
for (int i = 0; i < nboxes; ++i) {
Box* box = boxaGetBox(boxa, i, L_CLONE);
l_int32 x, y, box_width, box_height;
boxGetGeometry(box, &x, &y, &box_width, &box_height);
Pix* comp_pix = pixaGetPix(pixa, i, L_CLONE);
int max_width = MaxStrokeWidth(comp_pix);
pixDestroy(&comp_pix);
bool bad_line = false;
// If the length is too short to stand-alone as a line, and the box width
// is thick enough, and the stroke width is thick enough it is bad.
if (box_width >= kMinThickLineWidth && box_height >= kMinThickLineWidth &&
box_width < min_thick_length && box_height < min_thick_length &&
max_width > kMinThickLineWidth) {
// Too thick for the length.
bad_line = true;
}
if (!bad_line &&
(intersection_pix == NULL ||
NumTouchingIntersections(box, intersection_pix) < 2)) {
// Test non-line density near the line.
int nonline_count = CountPixelsAdjacentToLine(max_width, box,
nonline_pix);
if (nonline_count > box_height * box_width * kMaxNonLineDensity)
bad_line = true;
}
if (bad_line) {
// Not a good line.
pixClearInRect(line_pix, box);
--remaining_boxes;
}
boxDestroy(&box);
}
pixaDestroy(&pixa);
boxaDestroy(&boxa);
return remaining_boxes;
}
// Finds vertical and horizontal line objects in the given pix.
// Uses the given resolution to determine size thresholds instead of any
// that may be present in the pix.
// The output vertical_x and vertical_y contain a sum of the output vectors,
// thereby giving the mean vertical direction.
// If pix_music_mask != NULL, and music is detected, a mask of the staves
// and anything that is connected (bars, notes etc.) will be returned in
// pix_music_mask, the mask subtracted from pix, and the lines will not
// appear in v_lines or h_lines.
// The output vectors are owned by the list and Frozen (cannot refit) by
// having no boxes, as there is no need to refit or merge separator lines.
// The detected lines are removed from the pix.
void LineFinder::FindAndRemoveLines(int resolution, bool debug, Pix* pix,
int* vertical_x, int* vertical_y,
Pix** pix_music_mask,
TabVector_LIST* v_lines,
TabVector_LIST* h_lines) {
PERF_COUNT_START("FindAndRemoveLines")
if (pix == NULL || vertical_x == NULL || vertical_y == NULL) {
tprintf("Error in parameters for LineFinder::FindAndRemoveLines\n");
return;
}
Pix* pix_vline = NULL;
Pix* pix_non_vline = NULL;
Pix* pix_hline = NULL;
Pix* pix_non_hline = NULL;
Pix* pix_intersections = NULL;
Pixa* pixa_display = debug ? pixaCreate(0) : NULL;
GetLineMasks(resolution, pix, &pix_vline, &pix_non_vline, &pix_hline,
&pix_non_hline, &pix_intersections, pix_music_mask,
pixa_display);
// Find lines, convert to TabVector_LIST and remove those that are used.
FindAndRemoveVLines(resolution, pix_intersections, vertical_x, vertical_y,
&pix_vline, pix_non_vline, pix, v_lines);
if (pix_hline != NULL) {
// Recompute intersections and re-filter false positive h-lines.
if (pix_vline != NULL)
pixAnd(pix_intersections, pix_vline, pix_hline);
else
pixDestroy(&pix_intersections);
if (!FilterFalsePositives(resolution, pix_non_hline, pix_intersections,
pix_hline)) {
pixDestroy(&pix_hline);
}
}
FindAndRemoveHLines(resolution, pix_intersections, *vertical_x, *vertical_y,
&pix_hline, pix_non_hline, pix, h_lines);
if (pixa_display != NULL && pix_vline != NULL)
pixaAddPix(pixa_display, pix_vline, L_CLONE);
if (pixa_display != NULL && pix_hline != NULL)
pixaAddPix(pixa_display, pix_hline, L_CLONE);
if (pix_vline != NULL && pix_hline != NULL) {
// Remove joins (intersections) where lines cross, and the residue.
// Recalculate the intersections, since some lines have been deleted.
pixAnd(pix_intersections, pix_vline, pix_hline);
// Fatten up the intersections and seed-fill to get the intersection
// residue.
Pix* pix_join_residue = pixDilateBrick(NULL, pix_intersections, 5, 5);
pixSeedfillBinary(pix_join_residue, pix_join_residue, pix, 8);
// Now remove the intersection residue.
pixSubtract(pix, pix, pix_join_residue);
pixDestroy(&pix_join_residue);
}
// Remove any detected music.
if (pix_music_mask != NULL && *pix_music_mask != NULL) {
if (pixa_display != NULL)
pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
pixSubtract(pix, pix, *pix_music_mask);
}
if (pixa_display != NULL)
pixaAddPix(pixa_display, pix, L_CLONE);
pixDestroy(&pix_vline);
pixDestroy(&pix_non_vline);
pixDestroy(&pix_hline);
pixDestroy(&pix_non_hline);
pixDestroy(&pix_intersections);
if (pixa_display != NULL) {
#if LIBLEPT_MINOR_VERSION >= 69 || LIBLEPT_MAJOR_VERSION > 1
pixaConvertToPdf(pixa_display, resolution, 1.0f, 0, 0, "LineFinding",
"vhlinefinding.pdf");
#endif
pixaDestroy(&pixa_display);
}
PERF_COUNT_END
}
// Converts the Boxa array to a list of C_BLOB, getting rid of severely
// overlapping outlines and those that are children of a bigger one.
// The output is a list of C_BLOBs that are owned by the list.
// The C_OUTLINEs in the C_BLOBs contain no outline data - just empty
// bounding boxes. The Boxa is consumed and destroyed.
void LineFinder::ConvertBoxaToBlobs(int image_width, int image_height,
Boxa** boxes, C_BLOB_LIST* blobs) {
C_OUTLINE_LIST outlines;
C_OUTLINE_IT ol_it = &outlines;
// Iterate the boxes to convert to outlines.
int nboxes = boxaGetCount(*boxes);
for (int i = 0; i < nboxes; ++i) {
l_int32 x, y, width, height;
boxaGetBoxGeometry(*boxes, i, &x, &y, &width, &height);
// Make a C_OUTLINE from the leptonica box. This is a bit of a hack,
// as there is no outline, just a bounding box, but with some very
// small changes to coutln.cpp, it works nicely.
ICOORD top_left(x, y);
ICOORD bot_right(x + width, y + height);
CRACKEDGE startpt;
startpt.pos = top_left;
C_OUTLINE* outline = new C_OUTLINE(&startpt, top_left, bot_right, 0);
ol_it.add_after_then_move(outline);
}
// Use outlines_to_blobs to convert the outlines to blobs and find
// overlapping and contained objects. The output list of blobs in the block
// has all the bad ones filtered out and deleted.
BLOCK block;
ICOORD page_tl(0, 0);
ICOORD page_br(image_width, image_height);
outlines_to_blobs(&block, page_tl, page_br, &outlines);
// Transfer the created blobs to the output list.
C_BLOB_IT blob_it(blobs);
blob_it.add_list_after(block.blob_list());
// The boxes aren't needed any more.
boxaDestroy(boxes);
}
// Finds vertical line objects in pix_vline and removes the from src_pix.
// Uses the given resolution to determine size thresholds instead of any
// that may be present in the pix.
// The output vertical_x and vertical_y contain a sum of the output vectors,
// thereby giving the mean vertical direction.
// The output vectors are owned by the list and Frozen (cannot refit) by
// having no boxes, as there is no need to refit or merge separator lines.
// If no good lines are found, pix_vline is destroyed.
// None of the input pointers may be NULL, and if *pix_vline is NULL then
// the function does nothing.
void LineFinder::FindAndRemoveVLines(int resolution,
Pix* pix_intersections,
int* vertical_x, int* vertical_y,
Pix** pix_vline, Pix* pix_non_vline,
Pix* src_pix, TabVector_LIST* vectors) {
if (pix_vline == NULL || *pix_vline == NULL) return;
C_BLOB_LIST line_cblobs;
BLOBNBOX_LIST line_bblobs;
GetLineBoxes(false, *pix_vline, pix_intersections,
&line_cblobs, &line_bblobs);
int width = pixGetWidth(src_pix);
int height = pixGetHeight(src_pix);
ICOORD bleft(0, 0);
ICOORD tright(width, height);
FindLineVectors(bleft, tright, &line_bblobs, vertical_x, vertical_y, vectors);
if (!vectors->empty()) {
RemoveUnusedLineSegments(false, &line_bblobs, *pix_vline);
SubtractLinesAndResidue(*pix_vline, pix_non_vline, resolution, src_pix);
ICOORD vertical;
vertical.set_with_shrink(*vertical_x, *vertical_y);
TabVector::MergeSimilarTabVectors(vertical, vectors, NULL);
} else {
pixDestroy(pix_vline);
}
}
// Finds horizontal line objects in pix_hline and removes them from src_pix.
// Uses the given resolution to determine size thresholds instead of any
// that may be present in the pix.
// The output vertical_x and vertical_y contain a sum of the output vectors,
// thereby giving the mean vertical direction.
// The output vectors are owned by the list and Frozen (cannot refit) by
// having no boxes, as there is no need to refit or merge separator lines.
// If no good lines are found, pix_hline is destroyed.
// None of the input pointers may be NULL, and if *pix_hline is NULL then
// the function does nothing.
void LineFinder::FindAndRemoveHLines(int resolution,
Pix* pix_intersections,
int vertical_x, int vertical_y,
Pix** pix_hline, Pix* pix_non_hline,
Pix* src_pix, TabVector_LIST* vectors) {
if (pix_hline == NULL || *pix_hline == NULL) return;
C_BLOB_LIST line_cblobs;
BLOBNBOX_LIST line_bblobs;
GetLineBoxes(true, *pix_hline, pix_intersections, &line_cblobs, &line_bblobs);
int width = pixGetWidth(src_pix);
int height = pixGetHeight(src_pix);
ICOORD bleft(0, 0);
ICOORD tright(height, width);
FindLineVectors(bleft, tright, &line_bblobs, &vertical_x, &vertical_y,
vectors);
if (!vectors->empty()) {
RemoveUnusedLineSegments(true, &line_bblobs, *pix_hline);
SubtractLinesAndResidue(*pix_hline, pix_non_hline, resolution, src_pix);
ICOORD vertical;
vertical.set_with_shrink(vertical_x, vertical_y);
TabVector::MergeSimilarTabVectors(vertical, vectors, NULL);
// Iterate the vectors to flip them. x and y were flipped for horizontal
// lines, so FindLineVectors can work just with the vertical case.
// See GetLineBoxes for more on the flip.
TabVector_IT h_it(vectors);
for (h_it.mark_cycle_pt(); !h_it.cycled_list(); h_it.forward()) {
h_it.data()->XYFlip();
}
} else {
pixDestroy(pix_hline);
}
}
// Finds vertical lines in the given list of BLOBNBOXes. bleft and tright
// are the bounds of the image on which the input line_bblobs were found.
// The input line_bblobs list is const really.
// The output vertical_x and vertical_y are the total of all the vectors.
// The output list of TabVector makes no reference to the input BLOBNBOXes.
void LineFinder::FindLineVectors(const ICOORD& bleft, const ICOORD& tright,
BLOBNBOX_LIST* line_bblobs,
int* vertical_x, int* vertical_y,
TabVector_LIST* vectors) {
BLOBNBOX_IT bbox_it(line_bblobs);
int b_count = 0;
// Put all the blobs into the grid to find the lines, and move the blobs
// to the output lists.
AlignedBlob blob_grid(kLineFindGridSize, bleft, tright);
for (bbox_it.mark_cycle_pt(); !bbox_it.cycled_list(); bbox_it.forward()) {
BLOBNBOX* bblob = bbox_it.data();
bblob->set_left_tab_type(TT_MAYBE_ALIGNED);
bblob->set_left_rule(bleft.x());
bblob->set_right_rule(tright.x());
bblob->set_left_crossing_rule(bleft.x());
bblob->set_right_crossing_rule(tright.x());
blob_grid.InsertBBox(false, true, bblob);
++b_count;
}
if (b_count == 0)
return;
// Search the entire grid, looking for vertical line vectors.
BlobGridSearch lsearch(&blob_grid);
BLOBNBOX* bbox;
TabVector_IT vector_it(vectors);
*vertical_x = 0;
*vertical_y = 1;
lsearch.StartFullSearch();
while ((bbox = lsearch.NextFullSearch()) != NULL) {
if (bbox->left_tab_type() == TT_MAYBE_ALIGNED) {
const TBOX& box = bbox->bounding_box();
if (AlignedBlob::WithinTestRegion(2, box.left(), box.bottom()))
tprintf("Finding line vector starting at bbox (%d,%d)\n",
box.left(), box.bottom());
AlignedBlobParams align_params(*vertical_x, *vertical_y, box.width());
TabVector* vector = blob_grid.FindVerticalAlignment(align_params, bbox,
vertical_x,
vertical_y);
if (vector != NULL) {
vector->Freeze();
vector_it.add_to_end(vector);
}
}
}
}
// Returns a Pix music mask if music is detected.
// Any vertical line that has at least 5 intersections in sufficient density
// is taken to be a bar. Bars are used as a seed and the entire touching
// component is added to the output music mask and subtracted from the lines.
// Returns NULL and does minimal work if no music is found.
static Pix* FilterMusic(int resolution, Pix* pix_closed,
Pix* pix_vline, Pix* pix_hline,
l_int32* v_empty, l_int32* h_empty) {
int max_stave_height = static_cast<int>(resolution * kMaxStaveHeight);
Pix* intersection_pix = pixAnd(NULL, pix_vline, pix_hline);
Boxa* boxa = pixConnComp(pix_vline, NULL, 8);
// Iterate over the boxes to find music bars.
int nboxes = boxaGetCount(boxa);
Pix* music_mask = NULL;
for (int i = 0; i < nboxes; ++i) {
Box* box = boxaGetBox(boxa, i, L_CLONE);
l_int32 x, y, box_width, box_height;
boxGetGeometry(box, &x, &y, &box_width, &box_height);
int joins = NumTouchingIntersections(box, intersection_pix);
// Test for the join density being at least 5 per max_stave_height,
// ie (joins-1)/box_height >= (5-1)/max_stave_height.
if (joins >= 5 && (joins - 1) * max_stave_height >= 4 * box_height) {
// This is a music bar. Add to the mask.
if (music_mask == NULL)
music_mask = pixCreate(pixGetWidth(pix_vline), pixGetHeight(pix_vline),
1);
pixSetInRect(music_mask, box);
}
boxDestroy(&box);
}
boxaDestroy(&boxa);
pixDestroy(&intersection_pix);
if (music_mask != NULL) {
// The mask currently contains just the bars. Use the mask as a seed
// and the pix_closed as the mask for a seedfill to get all the
// intersecting staves.
pixSeedfillBinary(music_mask, music_mask, pix_closed, 8);
// Filter out false positives. CCs in the music_mask should be the vast
// majority of the pixels in their bounding boxes, as we expect just a
// tiny amount of text, a few phrase marks, and crescendo etc left.
Boxa* boxa = pixConnComp(music_mask, NULL, 8);
// Iterate over the boxes to find music components.
int nboxes = boxaGetCount(boxa);
for (int i = 0; i < nboxes; ++i) {
Box* box = boxaGetBox(boxa, i, L_CLONE);
Pix* rect_pix = pixClipRectangle(music_mask, box, NULL);
l_int32 music_pixels;
pixCountPixels(rect_pix, &music_pixels, NULL);
pixDestroy(&rect_pix);
rect_pix = pixClipRectangle(pix_closed, box, NULL);
l_int32 all_pixels;
pixCountPixels(rect_pix, &all_pixels, NULL);
pixDestroy(&rect_pix);
if (music_pixels < kMinMusicPixelFraction * all_pixels) {
// False positive. Delete from the music mask.
pixClearInRect(music_mask, box);
}
boxDestroy(&box);
}
l_int32 no_remaining_music;
boxaDestroy(&boxa);
pixZero(music_mask, &no_remaining_music);
if (no_remaining_music) {
pixDestroy(&music_mask);
} else {
pixSubtract(pix_vline, pix_vline, music_mask);
pixSubtract(pix_hline, pix_hline, music_mask);
// We may have deleted all the lines
pixZero(pix_vline, v_empty);
pixZero(pix_hline, h_empty);
}
}
return music_mask;
}
// Most of the heavy lifting of line finding. Given src_pix and its separate
// resolution, returns image masks:
// pix_vline candidate vertical lines.
// pix_non_vline pixels that didn't look like vertical lines.
// pix_hline candidate horizontal lines.
// pix_non_hline pixels that didn't look like horizontal lines.
// pix_intersections pixels where vertical and horizontal lines meet.
// pix_music_mask candidate music staves.
// This function promises to initialize all the output (2nd level) pointers,
// but any of the returns that are empty will be NULL on output.
// None of the input (1st level) pointers may be NULL except pix_music_mask,
// which will disable music detection, and pixa_display.
void LineFinder::GetLineMasks(int resolution, Pix* src_pix,
Pix** pix_vline, Pix** pix_non_vline,
Pix** pix_hline, Pix** pix_non_hline,
Pix** pix_intersections, Pix** pix_music_mask,
Pixa* pixa_display) {
Pix* pix_closed = NULL;
Pix* pix_hollow = NULL;
int max_line_width = resolution / kThinLineFraction;
int min_line_length = resolution / kMinLineLengthFraction;
if (pixa_display != NULL) {
tprintf("Image resolution = %d, max line width = %d, min length=%d\n",
resolution, max_line_width, min_line_length);
}
int closing_brick = max_line_width / 3;
PERF_COUNT_START("GetLineMasksMorph")
// only use opencl if compiled w/ OpenCL and selected device is opencl
#ifdef USE_OPENCL
if (OpenclDevice::selectedDeviceIsOpenCL()) {
// OpenCL pixGetLines Operation
int clStatus = OpenclDevice::initMorphCLAllocations(pixGetWpl(src_pix),
pixGetHeight(src_pix),
src_pix);
bool getpixclosed = pix_music_mask != NULL ? true : false;
OpenclDevice::pixGetLinesCL(NULL, src_pix, pix_vline, pix_hline,
&pix_closed, getpixclosed, closing_brick,
closing_brick, max_line_width, max_line_width,
min_line_length, min_line_length);
} else {
#endif
// Close up small holes, making it less likely that false alarms are found
// in thickened text (as it will become more solid) and also smoothing over
// some line breaks and nicks in the edges of the lines.
pix_closed = pixCloseBrick(NULL, src_pix, closing_brick, closing_brick);
if (pixa_display != NULL)
pixaAddPix(pixa_display, pix_closed, L_CLONE);
// Open up with a big box to detect solid areas, which can then be subtracted.
// This is very generous and will leave in even quite wide lines.
Pix* pix_solid = pixOpenBrick(NULL, pix_closed, max_line_width,
max_line_width);
if (pixa_display != NULL)
pixaAddPix(pixa_display, pix_solid, L_CLONE);
pix_hollow = pixSubtract(NULL, pix_closed, pix_solid);
pixDestroy(&pix_solid);
// Now open up in both directions independently to find lines of at least
// 1 inch/kMinLineLengthFraction in length.
if (pixa_display != NULL)
pixaAddPix(pixa_display, pix_hollow, L_CLONE);
*pix_vline = pixOpenBrick(NULL, pix_hollow, 1, min_line_length);
*pix_hline = pixOpenBrick(NULL, pix_hollow, min_line_length, 1);
pixDestroy(&pix_hollow);
#ifdef USE_OPENCL
}
#endif
PERF_COUNT_END
// Lines are sufficiently rare, that it is worth checking for a zero image.
l_int32 v_empty = 0;
l_int32 h_empty = 0;
pixZero(*pix_vline, &v_empty);
pixZero(*pix_hline, &h_empty);
if (pix_music_mask != NULL) {
if (!v_empty && !h_empty) {
*pix_music_mask = FilterMusic(resolution, pix_closed,
*pix_vline, *pix_hline,
&v_empty, &h_empty);
} else {
*pix_music_mask = NULL;
}
}
pixDestroy(&pix_closed);
Pix* pix_nonlines = NULL;
*pix_intersections = NULL;
Pix* extra_non_hlines = NULL;
if (!v_empty) {
// Subtract both line candidates from the source to get definite non-lines.
pix_nonlines = pixSubtract(NULL, src_pix, *pix_vline);
if (!h_empty) {
pixSubtract(pix_nonlines, pix_nonlines, *pix_hline);
// Intersections are a useful indicator for likelihood of being a line.
*pix_intersections = pixAnd(NULL, *pix_vline, *pix_hline);
// Candidate vlines are not hlines (apart from the intersections)
// and vice versa.
extra_non_hlines = pixSubtract(NULL, *pix_vline, *pix_intersections);
}
*pix_non_vline = pixErodeBrick(NULL, pix_nonlines, kMaxLineResidue, 1);
pixSeedfillBinary(*pix_non_vline, *pix_non_vline, pix_nonlines, 8);
if (!h_empty) {
// Candidate hlines are not vlines.
pixOr(*pix_non_vline, *pix_non_vline, *pix_hline);
pixSubtract(*pix_non_vline, *pix_non_vline, *pix_intersections);
}
if (!FilterFalsePositives(resolution, *pix_non_vline, *pix_intersections,
*pix_vline))
pixDestroy(pix_vline); // No candidates left.
} else {
// No vertical lines.
pixDestroy(pix_vline);
*pix_non_vline = NULL;
if (!h_empty) {
pix_nonlines = pixSubtract(NULL, src_pix, *pix_hline);
}
}
if (h_empty) {
pixDestroy(pix_hline);
*pix_non_hline = NULL;
if (v_empty) {
return;
}
} else {
*pix_non_hline = pixErodeBrick(NULL, pix_nonlines, 1, kMaxLineResidue);
pixSeedfillBinary(*pix_non_hline, *pix_non_hline, pix_nonlines, 8);
if (extra_non_hlines != NULL) {
pixOr(*pix_non_hline, *pix_non_hline, extra_non_hlines);
pixDestroy(&extra_non_hlines);
}
if (!FilterFalsePositives(resolution, *pix_non_hline, *pix_intersections,
*pix_hline))
pixDestroy(pix_hline); // No candidates left.
}
if (pixa_display != NULL) {
if (*pix_vline != NULL) pixaAddPix(pixa_display, *pix_vline, L_CLONE);
if (*pix_hline != NULL) pixaAddPix(pixa_display, *pix_hline, L_CLONE);
if (pix_nonlines != NULL) pixaAddPix(pixa_display, pix_nonlines, L_CLONE);
if (*pix_non_vline != NULL)
pixaAddPix(pixa_display, *pix_non_vline, L_CLONE);
if (*pix_non_hline != NULL)
pixaAddPix(pixa_display, *pix_non_hline, L_CLONE);
if (*pix_intersections != NULL)
pixaAddPix(pixa_display, *pix_intersections, L_CLONE);
if (pix_music_mask != NULL && *pix_music_mask != NULL)
pixaAddPix(pixa_display, *pix_music_mask, L_CLONE);
}
pixDestroy(&pix_nonlines);
}
// Returns a list of boxes corresponding to the candidate line segments. Sets
// the line_crossings member of the boxes so we can later determin the number
// of intersections touched by a full line.
void LineFinder::GetLineBoxes(bool horizontal_lines,
Pix* pix_lines, Pix* pix_intersections,
C_BLOB_LIST* line_cblobs,
BLOBNBOX_LIST* line_bblobs) {
// Put a single pixel crack in every line at an arbitrary spacing,
// so they break up and the bounding boxes can be used to get the
// direction accurately enough without needing outlines.
int wpl = pixGetWpl(pix_lines);
int width = pixGetWidth(pix_lines);
int height = pixGetHeight(pix_lines);
l_uint32* data = pixGetData(pix_lines);
if (horizontal_lines) {
for (int y = 0; y < height; ++y, data += wpl) {
for (int x = kCrackSpacing; x < width; x += kCrackSpacing) {
CLEAR_DATA_BIT(data, x);
}
}
} else {
for (int y = kCrackSpacing; y < height; y += kCrackSpacing) {
memset(data + wpl * y, 0, wpl * sizeof(*data));
}
}
// Get the individual connected components
Boxa* boxa = pixConnComp(pix_lines, NULL, 8);
ConvertBoxaToBlobs(width, height, &boxa, line_cblobs);
// Make the BLOBNBOXes from the C_BLOBs.
C_BLOB_IT blob_it(line_cblobs);
BLOBNBOX_IT bbox_it(line_bblobs);
for (blob_it.mark_cycle_pt(); !blob_it.cycled_list(); blob_it.forward()) {
C_BLOB* cblob = blob_it.data();
BLOBNBOX* bblob = new BLOBNBOX(cblob);
bbox_it.add_to_end(bblob);
// Determine whether the line segment touches two intersections.
const TBOX& bbox = bblob->bounding_box();
Box* box = boxCreate(bbox.left(), bbox.bottom(),
bbox.width(), bbox.height());
bblob->set_line_crossings(NumTouchingIntersections(box, pix_intersections));
boxDestroy(&box);
// Transform the bounding box prior to finding lines. To save writing
// two line finders, flip x and y for horizontal lines and re-use the
// tab-stop detection code. For vertical lines we still have to flip the
// y-coordinates to switch from leptonica coords to tesseract coords.
if (horizontal_lines) {
// Note that we have Leptonica coords stored in a Tesseract box, so that
// bbox.bottom(), being the MIN y coord, is actually the top, so to get
// back to Leptonica coords in RemoveUnusedLineSegments, we have to
// use height - box.right() as the top, which looks very odd.
TBOX new_box(height - bbox.top(), bbox.left(),
height - bbox.bottom(), bbox.right());
bblob->set_bounding_box(new_box);
} else {
TBOX new_box(bbox.left(), height - bbox.top(),
bbox.right(), height - bbox.bottom());
bblob->set_bounding_box(new_box);
}
}
}
} // namespace tesseract.
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