   volume data ? (medical scan)
  I have volume data of a human torso.  (Specifically, I'm using theskeleton data from Chapter 40 of GPU Gems I, if anyone has the book.)In the sample code, the author does this to the volume data:ptr = image_;   GLubyte *qtr = image;   GLubyte v, val;   for (i = 0; i < Size; i++) { v = *(ptr++); val = (v < 64) ? 0 : v - 64; val = val >> 1; *(qtr++) = val; *(qtr++) = ((float)val)*0.93; *(qtr++) = ((float)val)*0.78; *(qtr++) = val;   }i.e., for each voxel (unsigned byte), he shifts it by 64 (or clamps tozero) and right shifts by one (divide by 2).If this isn't done, I found you see more of the skin of the body.  Butwhen this data manipulation is done, you see the skeleton.So somehow this manipulation is "removing the fleshy parts" of thevolume, and just leaving the bone.Can someone explain this?  What do the unsigned byte values typicallymean in these medical scans?   
  The data represents density information (0 being entirely sparse, 255 being entirely dense).I have this book at home, so I will check later. What I'm guessing is that the author is taking all volume elements with a density of less than x and assigning them a density of 0 (kind of like rounding a float down if <= 0.5, up if > 0.5).Effectively, it turns everything less than the density of bone into nothingness.   