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/*
This file is part of Page Layout Detection Tools.
This code 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 code 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 code; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <raster/deskewer.h>
#include <util/bitutil.h>
#include <math.h>
#include <memory.h>
namespace pagetools{
unsigned int
Deskewer::next_pow2(unsigned int n){
unsigned int retval=1;
while(retval<n){
retval<<=1;
}
return retval;
}
double
Deskewer::findSkew(const BWImage& img){
unsigned int w2=next_pow2(img.bytewidth());
unsigned int ssize=2*w2-1; // Size of sharpness table
unsigned int *sharpness=new unsigned int[ssize];
radon(img, 1, sharpness);
radon(img, -1, sharpness);
unsigned int i, imax=0;
unsigned int vmax=0;
double sum=0.;
for(i=0; i<ssize; i++){
unsigned int s=sharpness[i];
if(s>vmax){
imax=i;
vmax=s;
}
sum+=s;
}
unsigned int h=img.height();
if(vmax<=3*sum/h){ // Heuristics !!!
return 0;
}
int iskew= (int)imax-int(w2)+1;
delete[] sharpness;
return atan((double)iskew/(8*w2));
}
void
Deskewer::radon(const BWImage& img, int sign, unsigned int sharpness[]){
unsigned short int *p1_, *p2_; // Stored columnwise
unsigned int w2=next_pow2(img.bytewidth());
unsigned int w=img.bytewidth();
unsigned int h=img.height();
unsigned int s=h*w2;
p1_=new unsigned short int[s];
p2_=new unsigned short int[s];
// Fill in the first table
memset(p1_, 0, sizeof(unsigned short int)*s);
unsigned int ir, ic;
unsigned char const *bitcount=BitUtil::bitcount();
for(ir=0; ir<h; ir++){
unsigned char const *scl=img.scanline(ir);
for(ic=0; ic<w; ic++){
if(sign>0){
p1_[h*ic+ir]=bitcount[scl[w-1-ic]];
}else{
p1_[h*ic+ir]=bitcount[scl[ic]];
}
}
}
// Iterate
unsigned short int *x1=p1_;
unsigned short int *x2=p2_;
unsigned int step=1;
for(;;){
unsigned int i;
for(i=0; i<w2; i+=2*step){
unsigned int j;
for(j=0; j<step; j++){
// Columns-sources:
unsigned short int *s1=x1+h*(i+j);
unsigned short int *s2=x1+h*(i+j+step);
// Columns-targets:
unsigned short int *t1=x2+h*(i+2*j);
unsigned short int *t2=x2+h*(i+2*j+1);
unsigned int m;
for(m=0; m<h; m++){
t1[m]=s1[m];
t2[m]=s1[m];
if(m+j<h){
t1[m]+=s2[m+j];
}
if(m+j+1<h){
t2[m]+=s2[m+j+1];
}
}
}
}
// Swap the tables:
unsigned short int *aux=x1;
x1=x2;
x2=aux;
// Increase the step:
step*=2;
if(step>=w2) break;
}
// Now, compute the sum of squared finite differences:
for(ic=0; ic<w2; ic++){
unsigned int acc=0;
unsigned short int *col=x1+h*ic;
for(ir=0; ir+1<h; ir++){
int diff=(int)(col[ir])-(int)(col[ir+1]);
acc+=diff*diff;
}
sharpness[w2-1+sign*ic]=acc;
}
delete[] p1_;
delete[] p2_;
}
}//namespace pagetools
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