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); }