private ushort GetRGBA5551(Color c)
{
int val = 0;
val += (byte)(c.A > 0x80 ? 1 : 0);
val += convert8to5(c.R) << 11;
val += convert8to5(c.G) << 6;
val += convert8to5(c.B) << 1;
ushort v = (ushort)val;
return v;
}