imagequant/blur.c

133 lines
4.1 KiB
C

/*
© 2011-2015 by Kornel Lesiński.
This file is part of libimagequant.
libimagequant 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 3 of the License, or
(at your option) any later version.
libimagequant 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 libimagequant. If not, see <http://www.gnu.org/licenses/>.
*/
#include "libimagequant.h"
#include "pam.h"
#include "blur.h"
/*
Blurs image horizontally (width 2*size+1) and writes it transposed to dst (called twice gives 2d blur)
*/
static void transposing_1d_blur(unsigned char *restrict src, unsigned char *restrict dst, unsigned int width, unsigned int height, const unsigned int size)
{
assert(size > 0);
for(unsigned int j=0; j < height; j++) {
unsigned char *restrict row = src + j*width;
// accumulate sum for pixels outside line
unsigned int sum;
sum = row[0]*size;
for(unsigned int i=0; i < size; i++) {
sum += row[i];
}
// blur with left side outside line
for(unsigned int i=0; i < size; i++) {
sum -= row[0];
sum += row[i+size];
dst[i*height + j] = sum / (size*2);
}
for(unsigned int i=size; i < width-size; i++) {
sum -= row[i-size];
sum += row[i+size];
dst[i*height + j] = sum / (size*2);
}
// blur with right side outside line
for(unsigned int i=width-size; i < width; i++) {
sum -= row[i-size];
sum += row[width-1];
dst[i*height + j] = sum / (size*2);
}
}
}
/**
* Picks maximum of neighboring pixels (blur + lighten)
*/
LIQ_PRIVATE void liq_max3(unsigned char *src, unsigned char *dst, unsigned int width, unsigned int height)
{
for(unsigned int j=0; j < height; j++) {
const unsigned char *row = src + j*width,
*prevrow = src + (j > 1 ? j-1 : 0)*width,
*nextrow = src + MIN(height-1,j+1)*width;
unsigned char prev,curr=row[0],next=row[0];
for(unsigned int i=0; i < width-1; i++) {
prev=curr;
curr=next;
next=row[i+1];
unsigned char t1 = MAX(prev,next);
unsigned char t2 = MAX(nextrow[i],prevrow[i]);
*dst++ = MAX(curr,MAX(t1,t2));
}
unsigned char t1 = MAX(curr,next);
unsigned char t2 = MAX(nextrow[width-1],prevrow[width-1]);
*dst++ = MAX(t1,t2);
}
}
/**
* Picks minimum of neighboring pixels (blur + darken)
*/
LIQ_PRIVATE void liq_min3(unsigned char *src, unsigned char *dst, unsigned int width, unsigned int height)
{
for(unsigned int j=0; j < height; j++) {
const unsigned char *row = src + j*width,
*prevrow = src + (j > 1 ? j-1 : 0)*width,
*nextrow = src + MIN(height-1,j+1)*width;
unsigned char prev,curr=row[0],next=row[0];
for(unsigned int i=0; i < width-1; i++) {
prev=curr;
curr=next;
next=row[i+1];
unsigned char t1 = MIN(prev,next);
unsigned char t2 = MIN(nextrow[i],prevrow[i]);
*dst++ = MIN(curr,MIN(t1,t2));
}
unsigned char t1 = MIN(curr,next);
unsigned char t2 = MIN(nextrow[width-1],prevrow[width-1]);
*dst++ = MIN(t1,t2);
}
}
/*
Filters src image and saves it to dst, overwriting tmp in the process.
Image must be width*height pixels high. Size controls radius of box blur.
*/
LIQ_PRIVATE void liq_blur(unsigned char *src, unsigned char *tmp, unsigned char *dst, unsigned int width, unsigned int height, unsigned int size)
{
assert(size > 0);
if (width < 2*size+1 || height < 2*size+1) {
return;
}
transposing_1d_blur(src, tmp, width, height, size);
transposing_1d_blur(tmp, dst, height, width, size);
}