[vtk-developers] zlib

[Sebastien BARRE]

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.

> > 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.

> > 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.

>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" ?