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Pngout bug?

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• markcramer at 2004-11-09 06:37
  Hi Ken,
  
  I've noticed that Pngout (Oct 13 2004) occasionally produces Png's that Tweakpng (http://entropymine.com/jason/tweakpng/) says that Libpng barfs on '[libpng] invalid distances set', though Irfanview seems to display them ok.
  
  I can send you a few samples of the pngs and commands I used to produce them, I'd include them here, but I can't find any way to include a graphic in the post, this is my first post on the board, or if you are interested, I can send them direct?
  
  Reply here or at markcramer at yahoo dot com
• Awesoken at 2004-11-09 07:19
  A few weeks ago, somebody else pointed out this exact same bug to me. Actually, it's a bug in Zlib, not PNGOUT. As you probably know, just about every program in existence that has some kind of ZIP or PNG support (other than my stuff of course : ) uses Zlib. I even wrote Mark Adler (Zlib co-author) about it. Here's what he had to say:

  I believe that the bug you are experiencing is only in zlib 1.2.1, and it is fixed in zlib 1.2.2, which you can find here:
  
  http://www.zlib.net/

  Zlib 1.2.2 was released about a month ago. I could easily do a hack in PNGOUT to make it produce files that are compatible with your buggy software, but I don't think that's the right thing to do. Instead, you should be nagging Jason Summers (Tweakpng author) to upgrade his code to the latest version of zlib.
• markcramer at 2004-11-09 18:53
  Sorry, it wasn't meant to be a 'nag', hence the 'bug?'
  
  I'll email Jason.