/* [<][>][^][v][top][bottom][index][help] */
DEFINITIONS
This source file includes following definitions.
- marked
- print_filter_stats
- pixel_filter_by_matrix
- rec_generate_number_table
- pixel_filter_by_number
- rec_generate_tree
- pixel_filter_by_tree
- pixel_faxfilter
- print_pixel_env
- getpixel
- put
/*
This is a Optical-Character-Recognition program
Copyright (C) 2000-2006 Joerg Schulenburg
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
Joerg.Schulenburg@physik.uni-magdeburg.de */
/* Filter by tree, filter by number methods added by
* William Webber, william@williamwebber.com. */
#include "pgm2asc.h"
#include <assert.h>
#include <string.h>
/*
* Defining this causes assert() calls to be turned off runtime.
*
* This is normally taken care of by make.
*/
/* #define NDEBUG */
// ------------------ (&~7)-pixmap-functions ------------------------
/* test if pixel marked?
* Returns: 0 if not marked, least 3 bits if marked.
*/
int marked (pix * p, int x, int y) {
if (x < 0 || y < 0 || x >= p->x || y >= p->y)
return 0;
return (pixel_atp(p, x, y) & 7);
}
#define Nfilt3 6 /* number of 3x3 filter */
/*
* Filters to correct possible scanning or image errors.
*
* Each of these filters represents a 3x3 pixel area.
* 0 represents a white or background pixel, 1 a black or
* foreground pixel, and 2 represents a pixel of either value.
* Note that this differs from the meaning of pixel values in
* the image, where a high value means "white" (background),
* and a low value means "black" (foreground).
*
* These filters are applied to the 3x3 environment of a pixel
* to be retrieved from the image, centered around that pixel
* (that is, the to-be-retrieved pixel corresponds with the
* the fifth position of the filter).
* If the filter matches that pixel environment, then
* the returned value of the pixel is inverted (black->white
* or white->black).
*
* So, for instance, the second filter below matches this
* pattern:
*
* 000
* X0X
* 000
*
* and "fills in" the middle (retrieved) pixel to rejoin a line
* that may have been broken by a scanning or image error.
*/
const char filt3[Nfilt3][9]={
{0,0,0, 0,0,1, 1,0,0}, /* (-1,-1) (0,-1) (1,-1) (-1,0) (0,0) ... */
{0,0,0, 1,0,1, 0,0,0},
{1,0,0, 0,0,1, 0,0,0},
{1,1,0, 0,1,0, 2,1,1},
{0,0,1, 0,0,0, 2,1,0},
{0,1,0, 0,0,0, 1,2,0}
};
/* 2=ignore_pixel, 0=white_background, 1=black_pixel */
/*
* Filter by matrix uses the above matrix of filters directly. Pixel
* environments to be filtered are compared pixel by pixel against
* these filters.
*
* Filter by number converts these filters into integer representations
* and stores them in a table. Pixel environments are similarly
* converted to integers, and looked up in the table.
*
* Filter by tree converts these filters into a binary tree. Pixel
* environments are matched by traversing the tree.
*
* A typical performance ratio for these three methods is 20:9:7
* respectively (i.e., the tree method takes around 35% of the
* time of the matrix method).
*/
#define FILTER_BY_MATRIX 0
#define FILTER_BY_NUMBER 1
#define FILTER_BY_TREE 2
#define FILTER_METHOD FILTER_BY_TREE
/*
* Defining FILTER_CHECKED causes filter results from either the tree
* or the number method to be checked against results of the other
* two methods to ensure correctness. This is for bug checking purposes
* only.
*/
/* #define FILTER_CHECKED */
/*
* Defining FILTER_STATISTICS causes statistics to be kept on how many
* times the filters are tried, how many times a filter matches, and
* of these matches how many flip a black pixel to white, and how many
* the reverse. These statistics are printed to stderr at the end of
* the program run. Currently, statistics are only kept if the tree
* filter method is being used.
*/
/* #define FILTER_STATISTICS */
#ifdef FILTER_STATISTICS
static int filter_tries = 0;
static int filter_matches = 0;
static int filter_blackened = 0;
static int filter_whitened = 0;
#endif
#ifdef FILTER_STATISTICS
void print_filter_stats() {
fprintf(stderr, "\n# Error filter statistics: tries %d, matches %d, "
"blackened %d, whitened %d\n",
filter_tries, filter_matches, filter_blackened, filter_whitened);
}
#endif
#if FILTER_METHOD == FILTER_BY_MATRIX || defined(FILTER_CHECKED)
/*
* Filter the pixel at (x,y) by directly applying the matrix.
*/
int pixel_filter_by_matrix(pix * p, int x, int y) {
int i;
static char c33[9];
memset(c33, 0, sizeof(c33));
/* copy environment of a point (only highest bit)
bbg: FASTER now. It has 4 ifs less at least, 8 at most. */
if (x > 0) { c33[3] = pixel_atp(p,x-1, y )>>7;
if (y > 0) c33[0] = pixel_atp(p,x-1,y-1)>>7;
if (y+1 < p->y) c33[6] = pixel_atp(p,x-1,y+1)>>7;
}
if (x+1 < p->x) { c33[5] = pixel_atp(p,x+1, y )>>7;
if (y > 0) c33[2] = pixel_atp(p,x+1,y-1)>>7;
if (y+1 < p->y) c33[8] = pixel_atp(p,x+1,y+1)>>7;
}
if (y > 0) c33[1] = pixel_atp(p, x ,y-1)>>7;
c33[4] = pixel_atp(p, x , y )>>7;
if (y+1 < p->y) c33[7] = pixel_atp(p, x ,y+1)>>7;
/* do filtering */
for (i = 0; i < Nfilt3; i++)
if( ( (filt3[i][0]>>1) || c33[0]!=(1 & filt3[i][0]) )
&& ( (filt3[i][1]>>1) || c33[1]!=(1 & filt3[i][1]) )
&& ( (filt3[i][2]>>1) || c33[2]!=(1 & filt3[i][2]) )
&& ( (filt3[i][3]>>1) || c33[3]!=(1 & filt3[i][3]) )
&& ( (filt3[i][4]>>1) || c33[4]!=(1 & filt3[i][4]) )
&& ( (filt3[i][5]>>1) || c33[5]!=(1 & filt3[i][5]) )
&& ( (filt3[i][6]>>1) || c33[6]!=(1 & filt3[i][6]) )
&& ( (filt3[i][7]>>1) || c33[7]!=(1 & filt3[i][7]) )
&& ( (filt3[i][8]>>1) || c33[8]!=(1 & filt3[i][8]) ) ) {
return ((filt3[i][4])?JOB->cfg.cs:0);
}
return pixel_atp(p, x, y) & ~7;
}
#endif
#if FILTER_METHOD == FILTER_BY_NUMBER || defined(FILTER_CHECKED)
#define NUM_TABLE_SIZE 512 /* max value of 9-bit value */
/*
* Recursively generates entries in the number table for a matrix filter.
*
* gen_num_filt is the number representation of the matrix filter.
* This generation is handled recursively because this is the easiest
* way to handle 2 (either value) entries in the filter, which lead
* to 2 distinct entries in the number table (one for each alternate
* value).
*/
void rec_generate_number_table(char * num_table, const char * filter,
int i, unsigned short gen_num_filt) {
if (i == 9) {
/* Invert the value of the number representation, to reflect the
* fact that the "white" is 0 in the filter, 1 (high) in the image. */
gen_num_filt = ~gen_num_filt;
gen_num_filt &= 0x01ff;
assert(gen_num_filt < NUM_TABLE_SIZE);
num_table[gen_num_filt] = 1;
} else {
if (filter[i] == 0 || filter[i] == 2)
rec_generate_number_table(num_table, filter, i + 1, gen_num_filt);
if (filter[i] == 1 || filter[i] == 2) {
gen_num_filt |= (1 << (8 - i));
rec_generate_number_table(num_table, filter, i + 1, gen_num_filt);
}
}
}
/*
* Filter the pixel at (x, y) using a number table.
*
* Each filter can be converted into a 9-bit representation, where
* filters containing 2 (either value) pixels are converted into
* a separate numerical representation for each pixel, where position
* i in the filter corresponds to bit i in the number. Each resulting
* numerical representation N is represented as a 1 value in the Nth
* position of a lookup table. A pixel's environment is converted in
* the same way to a numeric representation P, and that environment
* matches a filter if num_table[P] == 1.
*/
int pixel_filter_by_number(pix * p, int x, int y) {
unsigned short val = 0;
static char num_table[NUM_TABLE_SIZE];
static int num_table_generated = 0;
if (!num_table_generated) {
int f;
memset(num_table, 0, sizeof(num_table));
for (f = 0; f < Nfilt3; f++)
rec_generate_number_table(num_table, filt3[f], 0, 0);
num_table_generated = 1;
}
/* calculate a numeric value for the 3x3 square around the pixel. */
if (x > 0) { val |= (pixel_atp(p,x-1, y )>>7) << (8 - 3);
if (y > 0) val |= (pixel_atp(p,x-1,y-1)>>7) << (8 - 0);
if (y+1 < p->y) val |= (pixel_atp(p,x-1,y+1)>>7) << (8 - 6);
}
if (x+1 < p->x) { val |= (pixel_atp(p,x+1, y )>>7) << (8 - 5);
if (y > 0) val |= (pixel_atp(p,x+1,y-1)>>7) << (8 - 2);
if (y+1 < p->y) val |= (pixel_atp(p,x+1,y+1)>>7) << (8 - 8);
}
if (y > 0) val |= (pixel_atp(p, x ,y-1)>>7) << (8 - 1);
val |= (pixel_atp(p, x , y )>>7) << (8 - 4);
if (y+1 < p->y) val |= (pixel_atp(p, x ,y+1)>>7) << (8 - 7);
assert(val < NUM_TABLE_SIZE);
if (num_table[val])
return (val & (1 << 4)) ? 0 : JOB->cfg.cs;
else
return pixel_atp(p, x, y) & ~7;
}
#endif
#if FILTER_METHOD == FILTER_BY_TREE || defined(FILTER_CHECKED)
#define TREE_ARRAY_SIZE 1024
/* 1+ number of nodes in a complete binary tree of height 10 */
/*
* Recursively generate a tree representation of a filter.
*/
void rec_generate_tree(char * tree, const char * filter, int i, int n) {
assert(i >= 0 && i <= 9);
assert(n < TREE_ARRAY_SIZE);
if (i == 9) {
if (filter[4] == 0)
tree[n] = 2;
else
tree[n] = 1;
return;
}
/* first iteration has n == -1, does not set any values of the tree,
just to find whether to start to the left or the right */
if (n != -1)
tree[n] = 1;
if (filter[i] == 0)
rec_generate_tree(tree, filter, i + 1, n * 2 + 2);
else if (filter[i] == 1)
rec_generate_tree(tree, filter, i + 1, n * 2 + 3);
else {
rec_generate_tree(tree, filter, i + 1, n * 2 + 2);
rec_generate_tree(tree, filter, i + 1, n * 2 + 3);
}
}
/*
* Filter the pixel at (x, y) using the tree method.
*
* Each filter is represented by a single branch of a binary
* tree, except for filters contain "either value" entries, which
* bifurcate at that point in the branch. Each white pixel in the filter
* is a left branch in the tree, each black pixel a right branch. The
* final node of a branch indicates whether this filter turns a white
* pixel black, or a black one white.
*
* We match a pixel's environment against this tree by similarly
* using the pixels in that environment to traverse the tree. If
* we run out of nodes before getting to the end of a branch, then
* the environment doesn't match against any of the filters represented
* by the tree. Otherwise, we return the value specified by the
* final node.
*
* Since the total tree size, even including missing nodes, is small
* (2 ^ 10), we can use a standard array representation of a binary
* tree, where for the node tree[n], the left child is tree[2n + 2],
* and the right tree[2n + 3]. The only information we want
* from a non-leaf node is whether it exists (that is, is part of
* a filter-representing branch). We represent this with the value
* 1 at the node's slot in the array, the contrary by 0. For the
* leaf node, 0 again represents non-existence, 1 that the filter
* represented by this branch turns a black pixel white, and 2 a
* white pixel black.
*/
int pixel_filter_by_tree(pix * p, int x, int y) {
static char tree[TREE_ARRAY_SIZE];
static int tree_generated = 0;
int n;
int pixel_val = pixel_atp(p, x, y) & ~7;
#ifdef FILTER_STATISTICS
static int registered_filter_stats = 0;
if (!registered_filter_stats) {
atexit(print_filter_stats);
registered_filter_stats = 1;
}
filter_tries++;
#endif /* FILTER_STATISTICS */
if (!tree_generated) {
int f;
memset(tree, 0, sizeof(tree));
for (f = 0; f < Nfilt3; f++) {
const char * filter = filt3[f];
rec_generate_tree(tree, filter, 0, -1);
}
tree_generated = 1;
}
n = -1;
/* Note that for the image, low is black, high is white, whereas
* for the filter, 0 is white, 1 is black. For the image, then,
* high (white) means go left, low (black) means go right. */
#define IS_BLACK(_dx,_dy) !(pixel_atp(p, x + (_dx), y + (_dy)) >> 7)
#define IS_WHITE(_dx,_dy) (pixel_atp(p, x + (_dx), y + (_dy)) >> 7)
#define GO_LEFT n = n * 2 + 2
#define GO_RIGHT n = n * 2 + 3
#define CHECK_NO_MATCH if (tree[n] == 0) return pixel_val
/* Top row */
if (y == 0) {
/* top 3 pixels off edge == black == right
n = 2 * (2 * (2 * -1 + 3) + 3) + 3 = 13 */
n = 13;
} else {
if (x == 0 || IS_BLACK(-1, -1))
GO_RIGHT;
else
GO_LEFT;
if (IS_WHITE(0, -1))
GO_LEFT;
else
GO_RIGHT;
CHECK_NO_MATCH;
if (x + 1 == p->x || IS_BLACK(+1, -1))
GO_RIGHT;
else
GO_LEFT;
CHECK_NO_MATCH;
}
/* Second row */
if (x == 0 || IS_BLACK(-1, 0))
GO_RIGHT;
else
GO_LEFT;
CHECK_NO_MATCH;
if (IS_WHITE(0, 0))
GO_LEFT;
else
GO_RIGHT;
CHECK_NO_MATCH;
if (x + 1 == p->x || IS_BLACK(+1, 0))
GO_RIGHT;
else
GO_LEFT;
CHECK_NO_MATCH;
/* bottom row */
if (y + 1 == p->y) {
/* bottom 3 pixels off edge == black == right
n' = 2 * (2 * (2n + 3) + 3) + 3
= 2 * (4n + 9) + 3
= 8n + 21 */
n = 8 * n + 21;
} else {
if (x == 0 || IS_BLACK(-1, +1))
GO_RIGHT;
else
GO_LEFT;
CHECK_NO_MATCH;
if (IS_WHITE(0, 1))
GO_LEFT;
else
GO_RIGHT;
CHECK_NO_MATCH;
if (x + 1 == p->x || IS_BLACK(+1, +1))
GO_RIGHT;
else
GO_LEFT;
}
assert(n < TREE_ARRAY_SIZE);
assert(tree[n] == 0 || tree[n] == 1 || tree[n] == 2);
CHECK_NO_MATCH;
#ifdef FILTER_STATISTICS
filter_matches++;
#endif
if (tree[n] == 1) {
#ifdef FILTER_STATISTICS
if (pixel_atp(p, x, y) < JOB->cfg.cs)
filter_whitened++;
#endif
return JOB->cfg.cs;
} else {
#ifdef FILTER_STATISTICS
if (pixel_atp(p, x, y) >= JOB->cfg.cs)
filter_blackened++;
#endif
return 0;
}
}
#endif /* FILTER_METHOD == FILTER_BY_TREE */
/*
* This simple filter attempts to correct "fax"-like scan errors.
*/
int pixel_faxfilter(pix *p, int x, int y) {
int r; // filter
r = pixel_atp(p,x,y)&~7;
/* {2,2,2, 2,0,1, 2,1,0} */
if ((r&128) && (~pixel_atp(p,x+1, y )&128)
&& (~pixel_atp(p, x ,y+1)&128)
&& ( pixel_atp(p,x+1,y+1)&128))
r = 64; /* faxfilter */
else
/* {2,2,2, 1,0,2, 0,1,2} */
if ((r&128) && (~pixel_atp(p,x-1, y )&128)
&& (~pixel_atp(p, x ,y+1)&128)
&& ( pixel_atp(p,x-1,y+1)&128))
r = 64; /* faxfilter */
return r & ~7;
}
#ifdef FILTER_CHECKED
/*
* Print out the 3x3 environment of a pixel as a 9-bit binary.
*
* For debugging purposes only.
*/
void print_pixel_env(FILE * out, pix * p, int x, int y) {
int x0, y0;
for (y0 = y - 1; y0 < y + 2; y0++) {
for (x0 = x - 1; x0 < x + 2; x0++) {
if (x0 < 0 || x0 >= p->x || y0 < 0 || y0 >= p->y)
fputc('?', out);
else if (pixel_atp(p, x0, y0) >> 7)
fputc('0', out);
else
fputc('1', out);
}
}
}
#endif
/* this function is heavily used
* test if pixel was set, remove low bits (marks) --- later with error-correction
* result depends on n_run, if n_run>0 filter are used
* Returns: pixel-color (without marks)
*/
int getpixel(pix *p, int x, int y){
if ( x < 0 || y < 0 || x >= p->x || y >= p->y )
return 255 & ~7;
/* filter will be used only once later, when vectorization replaces pixel
* processing
*/
if (JOB->tmp.n_run > 0) { /* use the filters (correction of errors) */
#if FILTER_METHOD == FILTER_BY_NUMBER
int pix = pixel_filter_by_number(p, x, y);
#ifdef FILTER_CHECKED
int pix2 = pixel_filter_by_matrix(p, x, y);
if (pix != pix2) {
fprintf(stderr,
"# BUG: pixel_filter: by number: %d; by matrix: %d, "
"by atp %d; env: ", pix, pix2, pixel_atp(p, x, y) & ~7);
print_pixel_env(stderr, p, x, y);
fputc('\n', stderr);
}
#endif /* FILTER_CHECKED */
return pix;
#elif FILTER_METHOD == FILTER_BY_MATRIX
return pixel_filter_by_matrix(p, x, y);
#elif FILTER_METHOD == FILTER_BY_TREE
int pix = pixel_filter_by_tree(p, x, y);
#ifdef FILTER_CHECKED
int pix2 = pixel_filter_by_matrix(p, x, y);
int pix3 = pixel_filter_by_number(p, x, y);
if (pix != pix2 || pix != pix3) {
fprintf(stderr,
"# BUG: pixel_filter: tree: %d; matrix: %d, "
"number: %d, atp %d; env: ", pix, pix2, pix3,
pixel_atp(p, x, y) & ~7);
print_pixel_env(stderr, p, x, y);
fputc('\n', stderr);
}
#endif /* FILTER_CHECKED */
return pix;
#else
#error FILTER_METHOD not defined
#endif /* FILTER_BY_NUMBER */
}
return (pixel_atp(p,x,y) & ~7);
}
/* modify pixel, test if out of range */
void put(pix * p, int x, int y, int ia, int io) {
if (x < p->x && x >= 0 && y >= 0 && y < p->y)
pixel_atp(p, x, y) = (pixel_atp(p, x, y) & ia) | io;
}