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/********************************************************************************
* *
* E Z C o l o r Q u a n t i z a t i o n *
* *
*********************************************************************************
* Copyright (C) 1999,2022 by Jeroen van der Zijp. All Rights Reserved. *
*********************************************************************************
* This library is free software; you can redistribute it and/or modify *
* it under the terms of the GNU Lesser General Public License as published by *
* the Free Software Foundation; either version 3 of the License, or *
* (at your option) any later version. *
* *
* This library 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 Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public License *
* along with this program. If not, see <http://www.gnu.org/licenses/> *
********************************************************************************/
#include "xincs.h"
#include "fxver.h"
#include "fxdefs.h"
#include "fxmath.h"
/*
Notes:
- Use fxezquantize for a quick test to see if the image contains
less than 256 colors; for example loading then saving back out
an 8-bit GIF image. This ensures that the original set of
colors is maintained.
*/
using namespace FX;
/*******************************************************************************/
namespace FX {
extern FXbool fxezquantize(FXuchar* dst,const FXColor* src,FXColor* colormap,FXint& actualcolors,FXint w,FXint h,FXint maxcolors);
// EZ quantization may be used if w*h<=maxcolors, or if the actual colors
// used is less than maxcolors; using fxezquantize assures that no
// loss of data occurs repeatedly loading and saving the same file!
FXbool fxezquantize(FXuchar* dst,const FXColor* src,FXColor* colormap,FXint& actualcolors,FXint w,FXint h,FXint maxcolors){
FXint npixels=w*h;
FXint ncolors=0;
FXColor color;
FXint i,p,x;
FXColor colortable[337]; // Colors encountered in image
FXushort mapindex[337]; // Map index assigned to color
FXASSERT(maxcolors<=256);
// Clear map index
memset(mapindex,0xff,sizeof(mapindex));
// Hash all colors from image
for(i=0; i<npixels; i++){
// Get pixel
color=src[i];
// Find position in table
p=color%337;
x=color%331+1;
while(mapindex[p]!=0xffff){ // Empty slot
if(colortable[p]==color) goto nxt;
p=(p+x)%337;
}
// If no more room in colormap, we failed
if(ncolors>=maxcolors) return false;
// Add new color
colortable[p]=color; // Add color to color hash table
colormap[ncolors]=color; // Add color to color map
mapindex[p]=ncolors; // Remember map index of this color
ncolors++;
// Next pixel
nxt:continue;
}
// Now loop through image, assigning map indices; all colors
// must be in the map, so each lookup will be successful.
for(i=0; i<npixels; i++){
// Get pixel
color=src[i];
// Find position in table
p=color%337;
x=color%331+1;
while(colortable[p]!=color){
p=(p+x)%337;
}
// Output map index
dst[i]=(FXuchar)mapindex[p];
}
// Actual number of colors used
actualcolors=ncolors;
return true;
}
}
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