CODE:

#include 
#include 
#include 

typedef struct {
	double r;
	double g;
	double b;
} rgb_t;

int main(int argc,char* argv[]) {
	FILE* fp;
	/*入力変数*/
	unsigned char header[0x36];
	unsigned char* data;
	int datasize;
	int xsize,ysize;
	int rivflag;
	/*中間変数*/
	rgb_t* colordata;
	int linesize;
	int x,y,yy,i;
	double mindist;
	double nowdist;
	int minindex;
	rgb_t gosa;
	/*出力変数*/
	int* outindex;
	unsigned char* outdata;
	int outsize;
	/*カラーテーブル*/
	const rgb_t colorlist[16]={
		{  0,  0,  0},
		{  0,  0,128},
		{  0,128,  0},
		{  0,128,128},
		{128,  0,  0},
		{128,  0,128},
		{128,128,  0},
		{128,128,128},
		{192,192,192},
		{  0,  0,255},
		{  0,255,  0},
		{  0,255,255},
		{255,  0,  0},
		{255,  0,255},
		{255,255,  0},
		{255,255,255},
	};
	const unsigned char colortable[4*16]={
		0x00,0x00,0x00,0x00,
		0x00,0x00,0x80,0x00,
		0x00,0x80,0x00,0x00,
		0x00,0x80,0x80,0x00,
		0x80,0x00,0x00,0x00,
		0x80,0x00,0x80,0x00,
		0x80,0x80,0x00,0x00,
		0x80,0x80,0x80,0x00,
		0xC0,0xC0,0xC0,0x00,
		0x00,0x00,0xFF,0x00,
		0x00,0xFF,0x00,0x00,
		0x00,0xFF,0xFF,0x00,
		0xFF,0x00,0x00,0x00,
		0xFF,0x00,0xFF,0x00,
		0xFF,0xFF,0x00,0x00,
		0xFF,0xFF,0xFF,0x00
	};
	/*引数チェック*/
	if(argc4 || (argc==4 && strcmp(argv[3],"/d"))) {
		fprintf(stderr,"Usage: fto16color   [/d]\n");
		fprintf(stderr,"/d: use error diffusion\n");
		return 1;
	}
	/*ファイルオープン*/
	fp=fopen(argv[1],"rb");
	if(fp==NULL) {
		fprintf(stderr,"Can't open input file.\n");
		return 2;
	}
	/*ヘッダの読み込み*/
	if(fread(header,1,sizeof(header),fp)!=sizeof(header)) {
		fprintf(stderr,"Can't read the header.\n");
		fclose(fp);
		return 3;
	}
	/*最初の部分の確認*/
	if(header[0]!=0x42 || header[1]!=0x4D) {
		fprintf(stderr,"This is not a bitmap file.\n");
		fclose(fp);
		return 4;
	}
	/*ビット数の確認*/
	if(header[0x1C]+(header[0x1D]0) {
						colordata[(y+1)*xsize+(x-1)].r+=gosa.r*3.0/16.0;
						colordata[(y+1)*xsize+(x-1)].g+=gosa.g*3.0/16.0;
						colordata[(y+1)*xsize+(x-1)].b+=gosa.b*3.0/16.0;
					}
				}
			}
		}
	}
	/*色のリストを開放*/
	free(colordata);
	/*出力データの作成*/
	linesize=xsize/2;
	if(xsize%2)linesize++;
	if(linesize%4)linesize+=4-linesize%4;
	outdata=calloc(ysize*linesize,1);
	if(outdata==NULL) {
		fprintf(stderr,"Can't allocate memory.(4)\n");
		free(outindex);
		return 12;
	}
	for(yy=0;yy> 8)&0xFF;
	header[0x04]=(outsize>>16)&0xFF;
	header[0x05]=(outsize>>24)&0xFF;
	outsize=ysize*linesize;
	/*画像データサイズ*/
	header[0x22]= outsize     &0xFF;
	header[0x23]=(outsize>> 8)&0xFF;
	header[0x24]=(outsize>>16)&0xFF;
	header[0x25]=(outsize>>24)&0xFF;
	/*ビット数*/
	header[0x1C]=0x04;
	/*ファイルに出力*/
	fp=fopen(argv[2],"wb");
	if(fp==NULL) {
		fprintf(stderr,"Can't open output file.\n");
		free(outdata);
		return 13;
	}
	if(fwrite(header,1,sizeof(header),fp)!=sizeof(header)) {
		fprintf(stderr,"File write failed.(1)\n");
		fclose(fp);
		free(outdata);
		return 14;
	}
	if(fwrite(colortable,1,sizeof(colortable),fp)!=sizeof(colortable)) {
		fprintf(stderr,"File write failed.(2)\n");
		fclose(fp);
		free(outdata);
		return 15;
	}
	if(fwrite(outdata,1,outsize,fp)!=outsize) {
		fprintf(stderr,"File write failed.(3)\n");
		fclose(fp);
		free(outdata);
		return 16;
	}
	/*ファイルクローズ*/
	fclose(fp);
	/*出力画像データの開放*/
	free(outdata);
	/*正常終了*/
	return 0;
}