[vtkusers] VTK24 vs. 312, quality and performance

Prabhu Ramachandran prabhu at aero.iitm.ernet.in
Thu Mar 22 23:45:35 EST 2001


>>>>> "Tom" == B75826  <smitty at kcc.com> writes:

    Tom> The first brings up the Interactor, and the second generates
    Tom> an animated gif file, showing the star rotating 360 degrees
    Tom> about its vertical axis.  Here's the sizes of the two gif
    Tom> files, and as you can see, the one from VTK 3.1.2 is over 12
    Tom> times the size of the gif from VTK 2.4:

    Tom> 	-rw-r--r-- 1 smitty mst 65589 Mar 22 14:06 star24.gif
    Tom> -rw-r--r-- 1 smitty mst 805580 Mar 22 13:29 star312.gif

    Tom> To give some measure of the difference in performance, using
    Tom> the Interactor, I left-clicked and dragged from the center to
    Tom> the edge of the rendering window, which of course causes the
    Tom> image to rotate.  Then I timed the rotation through 360
    Tom> degrees.  The rendering from VTK 2.4 takes 16 seconds, and
    Tom> that from vtk312 72 seconds, 4.5 times longer.

I havent looked at your code, but I read in the comments that you use
ImageMagick to convert ppm's to gif.  I think this is the source of
the problem.  Since Unisys patented the compression with gifs and
started enforcing the patent, most sensible Linux distributions avoid
shipping with libraries that use the compression.  The new
uncompressed gif library is usually called 'libungif'.  I think that
the basic problem is there.  This is the reason why you see a file
that is 12 times larger: No compression.  I believe that your SGI has
a libgif that does compression and ImageMagick on the SGI uses it.
Older linux distro's also shipped with these kind of libraries.  The
rendering time may be slower simply because the gif files are so large
and processing them will take longer.  I cannot explain the poor
quality of the rendering.

Hope this helps,


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