Fonction qui permet de convertir un rgb sur 16 bits en un rgb sur 32 bits
unsigned long rgb16_to_rgb32(unsigned short a)
{
unsigned short r = (a & 0xF800) ;
unsigned short g = (a & 0x07E0) ;
unsigned short b = (a & 0x001F);
return (r << 8) | (g << 5) | (b<<3);
}
