Thanks to Rafael Jannone (who shared his algorithm) they look almost identical.
Here the full package (including the C, the .exe and some test images):
Perceptual converter and euclidean converter
Note:
This converter works only on .TGA, the .PNG in the package are for running other converters that does not support .TGA (e.g. Jannones's one) and to do comparisons.
-----------------------------------------
This is the code, where the distances are computed according to a perceptually uniform color metric:
/*
---------------------------------------------------------------
TMSOPT v.0.1 - Eduardo A. Robsy Petrus & Arturo Ragozini 2007
Credits to Rafael Jannone for his Floyd-Steinberg implementation
---------------------------------------------------------------
TGA image converter (24 bpp, uncompressed) to TMS9918 format
---------------------------------------------------------------
Overview
---------------------------------------------------------------
Selects the best solution for each 8x1 pixel block
Optimization uses the following algorithm:
(a) Select one 1x8 block, select a couple of colors, apply
Floyd-Steinberg within the block, compute the squared error,
repeat for all 105 color combinations, keep the best couple
of colors.
(b) Apply Floyd-Steinberg to the current 1x8 block with the best
two colors selected before and spread the errors to the
adjacent blocks.
(c) repeat (a) and (b) on the next 1x8 block, scan all lines.
(d) Convert the image in pattern and color definitions (CHR & CLR)
To load in MSX basic use something like this:
10 screen 2: color 15,0,0
20 bload"FILE.CHR",s
30 bload"FILE.CLR",s
40 goto 40
---------------------------------------------------------------
Compilation instructions
---------------------------------------------------------------
Tested with GCC/Win32 [mingw]:
GCC TMSopt.c -oTMSopt.exe -O3 -s
It is standard C, so there is a fair chance of being portable!
NOTE
In the current release the name of the C file has become scr2floyd.c
---------------------------------------------------------------
History
---------------------------------------------------------------
Ages ago - algorithm created
16/05/2007 - first C version (RAW format)
17/05/2007 - TGA format included, some optimization included
18/05/2007 - Big optimization (200 times faster), support for
square errors
19/05/2007 - Floyd-Stenberg added, scaling for better rounding
24/05/2007 - Floyd-Stenberg included in the color optimization.
---------------------------------------------------------------
Legal disclaimer
---------------------------------------------------------------
Do whatever you want to do with this code/program.
Use at your own risk, all responsability would be declined.
It would be nice if you credit the authors, though.
---------------------------------------------------------------
*/
// Headers!
#include<stdio.h>
#include<time.h>
#include<limits.h>
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned short ushort;
typedef unsigned long ulong;
//#define DEBUG
#define scale 16
#define inrange8(t) ((t)<0) ? 0 :(((t)>255) ? 255:(t))
#define clamp(t) ((t)<0) ? 0 :(((t)>255*scale) ? 255*scale : (t))
typedef struct {
float r, g, b;
} RGB;
float ColourDistance(RGB e1, RGB e2)
{
float r,g,b;
float rmean;
e1.r/=scale;
e1.g/=scale;
e1.b/=scale;
e2.r/=scale;
e2.g/=scale;
e2.b/=scale;
rmean = ( (int)e1.r + (int)e2.r ) / 2 ;
r = ((int)e1.r - (int)e2.r);
g = ((int)e1.g - (int)e2.g);
b = ((int)e1.b - (int)e2.b);
// return r*r+g*g+b*b;
return ((((512+rmean)*r*r)/256) + 4*g*g + (((767-rmean)*b*b)/256));
}
// Just one function for everything
main(int argc, char **argv)
{
// Vars
FILE *file,*CHR,*CLR;
int bc,bp,i,j,x,y,c,p,k,MAXX,MAXY;
uint n,total=0,done=0,size;
char *name;
short image[512+2][512+2][3],header[18],palette[16][3];
// TMS9918 RGB palette - approximated 50Hz PAL values
uint pal[16][3]= {
{ 0,0,0}, // 0 Transparent
{ 0,0,0}, // 1 Black 0 0 0
{ 33,200,66}, // 2 Medium green 33 200 66
{ 94,220,120}, // 3 Light green 94 220 120
{ 84,85,237}, // 4 Dark blue 84 85 237
{ 125,118,252}, // 5 Light blue 125 118 252
{ 212,82,77}, // 6 Dark red 212 82 77
{ 66,235,245}, // 7 Cyan 66 235 245
{ 252,85,84}, // 8 Medium red 252 85 84
{ 255,121,120}, // 9 Light red 255 121 120
{ 212,193,84}, // A Dark yellow 212 193 84
{ 230,206,128}, // B Light yellow 230 206 128
{ 33,176,59}, // C Dark green 33 176 59
{ 201,91,186}, // D Magenta 201 91 186
{ 204,204,204}, // E Gray 204 204 204
{ 255,255,255} // F White 255 255 255
};
// Scale palette
for (i=0;i<16;i++)
for (k=0;k<3;k++)
palette[i][k] = scale*pal[i][k];
// Get time
clock();
// Application prompt
printf("TMSopt v.0.1 - TGA 24bpp to TMS9918 converter.\nCoded by Eduardo A. Robsy Petrus & Arturo Ragozini 2007.\n\n");
printf("Credits to Rafael Jannone for his Floyd-Steinberg implementation.\n \n");
// Guess the name of the image I used for testing
#ifdef DEBUG
argc = 2;
argv[1] = malloc(20);
argv[1][0] = 'l';
argv[1][1] = 'e';
argv[1][2] = 'n';
argv[1][3] = 'n';
argv[1][4] = 'a';
argv[1][5] = '_';
argv[1][6] = '.';
argv[1][7] = 't';
argv[1][8] = 'g';
argv[1][9] = 'a';
argv[1][10] = 0;
#endif
// Test if only one command-line parameter is available
if (argc==1)
{
printf("Syntax: TMSopt [file.tga]\n");
return;
}
// Open source image (TGA, 24-bit, uncompressed)
if ((file=fopen(argv[1],"rb"))==NULL)
{
printf("cannot open %s file!\n",argv[1]);
return;
}
// Read TGA header
for (i=0;i<18;i++) header[i]=fgetc(file);
// Check header info
for (i=0,n=0;i<12;i++) n+=header[i];
// I deleted the check on n, was it important ?
if ((header[2]!=2)||(header[17])||(header[16]!=24))
{
printf("Unsupported file format!\n");
return;
}
// Calculate size
MAXX=header[12]|header[13]<<8;
MAXY=header[14]|header[15]<<8;
size=((MAXX+7)>>3)*MAXY;
// Check size limits
if ((!MAXX)||(MAXX>512)||(!MAXY)||(MAXY>512))
{
printf("Unsupported size!");
return;
}
// Load image data
for (y=MAXY-1;y>=0;y--)
for (x=0;x<MAXX;x++)
for (k=0;k<3;k++)
image[x+1][y+1][2-k]=((short)fgetc(file))*scale; // Scale image
for (x=0;x<MAXX;x++)
for (k=0;k<3;k++)
image[x][0][k] = image[x][1][k];
for (y=0;y<MAXY;y++)
for (k=0;k<3;k++)
image[0][y][k] = image[1][0][k];
// Close file
fclose(file);
// Information
printf("Converting %s (%i,%i) to TMS9918 format ",argv[1],MAXX,MAXY);
printf("in (%i,%i) screen 2 tiles... ",((MAXX+7)>>3),((MAXY+7)>>3));
// Image processing
for (y=0;y<((MAXY+7)>>3);y++)
for (j=0;j<8;j++)
for (x=0;x<((MAXX+7)>>3);x++)
{
// Generate alternatives
uchar c1, c2;
uchar bc1, bc2;
uint bv;
uint bs = INT_MAX;
uint yy = 1+((y<<3)|j);
for (c1=1;c1<16;c1++)
{
RGB cp1 = {palette[c1][0],palette[c1][1],palette[c1][2]};
for (c2=c1+1;c2<16;c2++)
{
RGB cp2 = {palette[c2][0],palette[c2][1],palette[c2][2]};
uint xx = 1+(x<<3);
RGB ppp = {clamp(image[xx][yy][0]),clamp(image[xx][yy][1]),clamp(image[xx][yy][2])};
uint cs = 0;
uint cv = 0;
for (i=0;i<8;i++)
{
short e10 = (ppp.r-cp1.r);
short e11 = (ppp.g-cp1.g);
short e12 = (ppp.b-cp1.b);
long mc1 = ColourDistance(cp1,ppp);
short e20 = (ppp.r-cp2.r);
short e21 = (ppp.g-cp2.g);
short e22 = (ppp.b-cp2.b);
long mc2 = ColourDistance(cp2,ppp);
cs += (mc1>mc2) ? mc2 : mc1;
if (cs>bs) break;
cv |= ((mc1>mc2)<<i);
xx++;
if (mc1>mc2)
{
ppp.r = clamp(image[xx][yy][0]) + 7*e20/16;
ppp.g = clamp(image[xx][yy][1]) + 7*e21/16;
ppp.b = clamp(image[xx][yy][2]) + 7*e22/16;
}
else
{
ppp.r = clamp(image[xx][yy][0]) + 7*e10/16;
ppp.g = clamp(image[xx][yy][1]) + 7*e11/16;
ppp.b = clamp(image[xx][yy][2]) + 7*e12/16;
}
}
if (cs<bs)
{
bs = cs;
bv = cv;
bc1 = c1;
bc2 = c2;
}
}
}
// Here we have the best colors and the best pattern for line j
short quant_error;
uint xx = 1+((x<<3));
for (i=0;i<8;i++,xx++)
for (k=0;k<3;k++)
{
// Compute the quantization error
if (bv&(1<<i))
{
quant_error = (clamp(image[xx][yy][k]) - palette[bc2][k])/16;
image[xx][yy][k] = palette[bc2][k];
}
else
{
quant_error = (clamp(image[xx][yy][k]) - palette[bc1][k])/16;
image[xx][yy][k] = palette[bc1][k];
}
// Spread the quantization error
short q2 = quant_error<<1;
image[xx+1][yy+1][k] = clamp(image[xx+1][yy+1][k])+ quant_error; // 1 *
quant_error += q2 ;
image[xx-1][yy+1][k] = clamp(image[xx-1][yy+1][k])+ quant_error; // 3 *
quant_error += q2 ;
image[xx+0][yy+1][k] = clamp(image[xx+0][yy+1][k])+ quant_error; // 5 *
quant_error += q2 ;
image[xx+1][yy+0][k] = clamp(image[xx+1][yy+0][k])+ quant_error; // 7 *
}
// Update status counter
if (done*100/size<(done+1)*100/size)
printf("\b\b\b%2i%%",100*done/size);
done++;
total++;
}
// Conversion done
printf("\b\b\bOk \n");
// Create TMS output files (CHR, CLR)
argv[1][strlen(argv[1])-3]='C';
argv[1][strlen(argv[1])-2]='H';
argv[1][strlen(argv[1])-1]='R';
CHR=fopen(argv[1],"wb");
argv[1][strlen(argv[1])-2]='L';
CLR=fopen(argv[1],"wb");
fputc(0xFE,CLR); // Binary data
fputc(0x00,CLR); // Start at 2000h
fputc(0x20,CLR);
fputc(0xFF,CLR); // Stop at 37FFh
fputc(0x37,CLR);
fputc(0x00,CLR); // Run
fputc(0x00,CLR);
fputc(0xFE,CHR); // Binary data
fputc(0x00,CHR); // Start at 0000h
fputc(0x00,CHR);
fputc(0xFF,CHR); // Stop at 17FFh
fputc(0x17,CHR);
fputc(0x00,CHR); // Run
fputc(0x00,CHR);
// Save best pattern and colour combination
// NOTE1:
// THIS PART CAN BE LARGELY CUTTED AND OPTIMIZED REUSING
// RESULTS FROM THE PREVIOUS LOOP, BUT WHO CARES?
// NOTE2:
// This code can be used for conversion without dithering
for (y=0;y<((MAXY+7)>>3);y++)
for (x=0;(x<(MAXX+7)>>3);x++)
for (j=0;j<8;j++)
{
uchar c1,c2;
uint bs = INT_MAX;
uchar bp = 0, bc = 0;
uint yy = 1+((y<<3)|j);
for (c1=1;c1<16;c1++)
{
RGB cp1 = {palette[c1][0],palette[c1][1],palette[c1][2]};
for (c2=c1+1;c2<16;c2++)
{
RGB cp2 = {palette[c2][0],palette[c2][1],palette[c2][2]};
uint cs = 0;
uint cp = 0;
for (i=0;i<8;i++)
{
uint xx = 1+((x<<3)|i);
RGB ppp = {clamp(image[xx][yy][0]),clamp(image[xx][yy][1]),clamp(image[xx][yy][2])};
long mc1 = ColourDistance(cp1,ppp);
long mc2 = ColourDistance(cp2,ppp);
cp = (cp<<1) | (mc1>mc2);
cs += (mc1>mc2) ? mc2 : mc1;
if (cs>bs) break;
}
if (cs<bs)
{
bs=cs;
bp=cp;
bc=c2*16+c1;
}
}
}
fputc(bc,CLR);
fputc(bp,CHR);
}
fclose(CHR);
fclose(CLR);
// Generate new name
name = malloc(0x100);
argv[1][strlen(argv[1])-4]=0;
strcpy(name,argv[1]);
strcat(name,"_tms.tga");
// Save file header
file=fopen(name,"wb");
for (i=0;i<18;i++) fputc(header[i],file);
// Save image data
for (y=MAXY-1;y>=0;y--)
for (x=0;x<MAXX;x++)
for (k=0;k<3;k++)
fputc(inrange8(image[1+x][1+y][2-k]/scale),file); // Scale to char
// Close file
fclose(file);
// Prompt elapsed time
printf("%.2f million combinations analysed in %.2f seconds.\n",total/1e6,(float)clock()/(float)CLOCKS_PER_SEC);
printf("Note: the .CLR and .CHR files have correct headers only for 256x192 images. \n");
}
