Aaron Jones (aaron@arlut.utexas.edu)
Wed, 30 Jun 1999 16:23:06 -0500
At work we are experimenting using Volumizer to display data, and I have
run into some odd behavior, and was wondering if anyone could
explain/give some insight/had the same problem.
We are using the two ifl converters provided with Volumizer (iflfrombin
and iflto3Dtiff) to convert from our image file system to tiff. The
first problem that I was getting is that when using the iflfrombin the
image came out perfect...just flipped across the x-axis.
The next problem I encountered was that after converting to the tiff
format, and then using iflto3Dtiff to stack them up and display them
with perfvol, I was loosing essentially all images over approximately 30
(turned out to be 32). Well, long story short, a co-worker of mine and
myself came up with a "conjecture" that seems to govern pretty well how
it will behave:
1. if the number of stacked up images is a power of two greater than
4, it will display properly at the power of two, and one less than the
power of 2.
2. if the number of stacked is two less than a power of two greater
than 4, perfvol crashes before it finishes loading.
3. if the number of stacks is less than that, any thing above the next
lower power of two seemingly gets culled.
To test this, I made a program to construct a small square in a 256 x
256 image (the square itself was 10x10), for simplicity let's call it
01.tif, and then an image that was 256x256 of pure black, again for
simplicity Z.tif (Z for zeros).
iflto3Dtiff Z.tif Z.tif Z.tif Z.tif Z.tif 01.tif 3Dimage.tif; perfvol
3Dimage.tif would fall into that second clause and perfvol crashes
before doing anything.
iflto3Dtiff Z.tif Z.tif Z.tif Z.tif 01.tif 3Dimage.tif; perfvol
3Dimage.tif would fall into the first category and all that will
display is black.
etc.
What makes it more interesting is that the demos that came with
Volumizer were anything but exact powers of two (77, 38, 77 respectively
for CT.Head.Bone.char.tif, CT.Head.Small.char.tif, and CT.Head.char.tif)
and the 3D tiff provided worked beautifully. However, I tried
converting them with the two ifl manipulators and was not able to
duplicate the results. Does anyone know why the number of stacked
images(the z axis) seems to conform to this property? The x and y axis
is understandable, as it is done in texture memory, but it seems odd
that the z axis must also. Is this a side effect of iflto3Dtiff? Is it
a problem with pfVONode? Is it an accident happening inside of
Volumizer itself? Any insight or explanation would be GREATLY
appreciated.
Thanks for all help,
Aaron
This archive was generated by hypermail 2.0b2 on Mon Nov 01 1999 - 14:02:51 PST