On Thu, 18 Apr 2002, Herbert Voss wrote: > if we want to build up a 16bit color correct to > a 8 bit one than we cannot do only a shift of > 8 bit to get the high or low byte.
This is a very good approximation. > we had to take every second _bit_ from the original one. Or > every third if it's a 24 bit one. And for a 4 bit we > have to double the bits, not only shifting the > whole nibble. This is wrong. > I suppose, that xpm uses the same color modell > than all the other ones, but I'm not really sure. > so maybe that I'm wrong here You are both using a RGB color model, but this is not relevant. Even with a HSL or Munsell color space, the transformation would be the same: You want the Most Significant Bits. Why? Because you loose more information by dropping more significant bits. So, you should take the upper 8 bits, and if you want to do better than that, round according to the 7th bit. If you do not believe me, try to convert a photo with colors using both approaches, and see for yourselves. Greets, Asger
