[conspire] [Gimp-user] PNG troubles

[Ruben Safir]

On Fri, Aug 10, 2018 at 02:06:04PM -0700, Rick Moen wrote:
> Quoting Ruben Safir (ruben at mrbrklyn.com):
> 
> > > Your claim that PNG is wholly undependable and not a usable format is
> > > _also_ grossly inaccurate.  
> > 
> > Its not a claim but a hypothesis based on experience.  twice in 20 years
> > I found problems with previously made PNG files that later failed to be
> > renderable by the (at the time) current PNG.
> 
> It was a non-sequitur the first time you said it, and it remains one
> upon further repetition.
> 
> I see no reason to dispute the matter with you further, 

I see no reason to have a dispute at all.


> as I think the
> point is pretty obvious:  The PNG specification doesn't say how zlib
> compression should work[1], much less is it the fault of the specification
> that a zlib implementation leveraged by a long-ago release of libpng
> calculated incorrect zlib checksums, and a later implementation enforced
> valid zlib checksums.
> 

http://libpng.org/pub/png/spec/1.2/PNG-Compression.html

I don't know if you are off on a tanget or whatever, but if PNG wasn't
specific about how the files decompressed, it would be useless
altogether for saving archival image files.

> All of the effort you're spending generating online gratuitous drama
> would be better spent compiling and using PNG utilities to correct your 
> slightly defective old images.
> 

This is a bit insulting and is not true.  There is nothing gratuitous
about losing access to file that include rare photographs and scans of
relatives who are no longer with us.

I don't really care what the PNG specification says, when it comes to
brass tacks. If I create files with PNG formating I want access to them
forever.  If it is speciic enough and clear enough in its implementation
to do that (that is a hypothesis btw), then I can use it.  If not, then
I need to reconsider them format and not use it.


The only drama is in this email.


> > They seem to have a small application which fixes the files I showed
> > them, so that is good.
> 
> Great.  Use it.  Lose the drama.
> 
> 
> If you decide you don't like PNG, you're free to convert your files over
> to GIF and use that.  Happy ending.
> 

Probably to tif.

> 
> [1] As you probably know, that spec is defined in RFC-1950.  The PNG
> spec does constrain what -subtype- of zlib compression may be used.
> http://www.libpng.org/pub/png/spec/1.2/PNG-Compression.html
> 
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