[vtkusers] Re: VTK24 vs. 312, quality and performance

Tom G. Smith (B75826) smitty at kcc.com
Fri Mar 23 08:25:51 EST 2001

Prabhu hit the nail squarely on the head regarding the ImageMagick
convert utility not using compression in RH7.  The original ppm files
were all 270015 bytes, and the gif files out of the convert utility
are all 91492 bytes on the RH7 system, and range from 4178 to 8629
bytes on the older SGI system.

That explains the gif file size differences, but still doesn't address
the performance and rendering quality issues.  My performance test was
done with the VTK Interactor, and a GIF file was not involved there,
just vtk:  vtk star.tcl -- -c yellow.  Regarding the rendering quality,
there are artifacts that shouldn't be there, shadows have sharp edges
where they should be blended, and objects are clipped where they shouldn't
be.  The best description I can give, it looks like Andy Warhol had an
influence in the renderings from VTK 3.1.2 :-)

Forwarded message:
> From: "Prabhu Ramachandran" <prabhu at aero.iitm.ernet.in>
> Date: Fri, 23 Mar 2001 10:15:35 +0530 (IST)
> To: "Tom G. Smith (B75826)" <smitty at kcc.com>,
>    "VTK users list" <vtkusers at public.kitware.com>
> Subject: [vtkusers] VTK24 vs. 312, quality and performance
> hi,
> >>>>> "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,
> prabhu


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