void pixel_write(int i, int j){
static unsigned char color[6];
unsigned short red = red_fn(i,j)&DM1, blue = blue_fn(i,j)&DM1, green = green_fn(i,j)&DM1;
color[1] = red&255;
color[0] = red>>8;
color[3] = green&255;
color[2] = green>>8;
color[5] = blue&255;
color[4] = blue>>8;
fwrite(color, 1, 6, fp);
}