[vtk-developers] zlib

[Michael Halle]

I know that there's been a long-standing philosophy that vtk is
easiest maintained when it is standalone, not dependent on outside
libraries except when essential.  I would like to discuss the
possibility of making an exception and adding zlib to a future vtk
release.

Why?  Here's my list.

* Many of the data and image files in visualization are enormous, yet
  sparse. A standard compression would be extremely helpful, and improve 
  the speed of loading over network-mounted disks or the net.

* vtk files can remain readable across all platforms if a standardized
  compression scheme is used.

* it is compatible with the compression format of common utilities
  such as gzip.

* with zlib, it's possible to read and write PNG files, which support
  up-to-16 bit grayscale images, 48 bit truecolor images, color-palette
  images, and alpha transparency.  PNG is a very simple format (simpler
  than TIFF), so you don't really need libpng, but you need to have
  zip compression.

* if it's a vtk standard, then core classes can wrap it in a way that
  abstracts and isolates users from the details of reading/writing
  compressed streams.

* zip compression is pretty good -- in the worst case, it almost never
  makes files bigger.

* zlib is patent unencumbered and usable for any purpose.

* zlib is quite stable - it doesn't need to be updated often, if ever.
  The latest release (1.1.3) came out in 1998.

* it's very portable (compiles across more platforms than vtk).

* it's very small.

* it's not worth trying to reimplement the library.

* other software (cvs, for example) includes zlib for exactly these
  reasons.


Anyone else have thoughts on this idea?

Thanks.

Michael Halle
mhalle at media.mit.edu