Raster format incompatibilities

[Steve Franklin]

   Although I never would have guessed it, I am back using GRASS for some
tasks at a new job with a university. The task isn't necessarily GIS
oriented, but GRASS seems to be perfect for the task of digitization MRI
scans of the upper torso and internal organs of the body. From this we are
able to assemble three dimensional images that help us understand greatly
the propagation of electric fields through the upper chest from the heart.
As I'm playing with GRASS and getting reaquainted, I'm running into some
problems that I had had two years ago, and I"m hoping that a solution has
been found since then.

1) We're starting with tif images, and I've always wanted to be able to type:
tifftopnm file.tif | pnmtorast -standard > file.ras
Then of course, I'd do an r.in.sunrast on the file. Unfortunately, Grass
doesn't seem to like the format of the files? I can't understand it. I've
been using xv to save the tif to a sunrast file, and it works okay, but with
50 files per batch, I don't have the time to do this. xv says that they're
both pretty much the same type of file, but the pnmtorast'd file is a bit
shorter, implying a different header perhaps. Has anyone found an easy way
to do this? Am I doing something wrong?

2) We'll be working with greyscale images, and I can't seem to trick grass
into giving me more than 8 greyscales of resolution. I remember discussing
within this forum this problem years ago, and no one was able to come up
with a solution... Is there any better alternative? Incedentally, we are
running grass 4.0. We just don't have the disk space for 4.1, or the need
for that matter... 

Any fixes or solutions would be greatly appreciated. Mail can be directed to
franklin at ug.cs.dal.ca

   Thanks in advance,

Steve Franklin, Dalhousie University
Biophysics