[vtk-developers] zlib

[David Gobbi]

On Wed, 1 Nov 2000, Sebastien BARRE wrote:

> At 01/11/00 13:06, David Gobbi wrote:
> >
> > > I do agree with you, zlib is a good candidate, I've been using it 
> > myself as
> > > part of a freeware I've written, and it is very easy to use. The static 
> > lib
> > > is small.
> >
> >I disagree... what someone should do is take this opportunity to
> >demonstrate how to add _extensions_ to VTK
> 
> Nobody said the contrary.

I thought that Michael was suggesting that the zlib source should be
included with VTK?
 
> > > As the vtkdata and vtkbaseline are growing and growing, we could shrink
> > > them easily.
> >
> >Using compression would only shrink them to about 1/2 or 1/4 their
> >original size.   With disk space as cheap as it is these days, I never
> >compress my files unless I'm archiving them.  My CPU has better things
> >to do than compress and uncompress 40MB data files.
> 
> All right, let's all use BMP then ? Let's discard Jpeg, GIF ? Are you going 
> to discuss the benefit of graphics compression ? Compression is also useful 
> for network issues. Even though, this is not so easy to compare : CPU are 
> getting faster every year than disks are, there *are* cases where reading 
> 1/10 th of a compressed file then decompressing it is faster then reading 
> the whole uncompressed file. And these smaller file are easier to put in 
> the disk or memory cache, thus reading is even more cheaper.

Okay, okay.  When I shoot my mouth off, I guess I deserve to get an
earfull in return.  What I said doesn't make all that much sense.

> > > But as we already have a TIFF writer, we might be able to use the zlib
> > > compression scheme in TIFF.
> >
> >This would be an EXTREMELY bad idea.  The standard compression scheme in
> >LZW, which is incompatible with zlib.  Do we want VTK to write TIFF files
> >that can't be read by other software?
> 
> OK, calm down ! I did not check that the scheme was LZW only, I thought 
> there was an option for a gzip compression scheme, there is no need to yell 
> at me.

Sorry.  As my PhD progresses, the gentler aspects of my personality
are slowly being eroded away ;)  I'll just leave as "I don't think it
would be a good idea to use zlib compression with TIFF because of
compatibility issues with other software."

> >So, here's how things should proceed (IMHO):
> >
> >1) someone should write a vtkPNGReader, which can go in 'vtk/local'
> >
> >2) at least someone else should test it
> >
> >3) modify 'configure' or 'pcmaker' to check for either libpng or
> >    for the libpng source code,
> 
> and compile it ? so what's the difference ? Do you think I was talking 
> about forcing the user to download zlib, and crash the compilation process 
> if it was not there... "sorry, no zlib, goodbye" ?

I don't think that the zlib source should come with VTK, or that users
should be forced to download it _unless_ they want to use the compression
with VTK.  I think it should be an option.

 - David
 
--
  David Gobbi, MSc                    dgobbi at irus.rri.on.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario