Re: Why is it that png files are not dependable over the long haul

Greg Roelofs wrote:
> If that's actually the root of the problem, then the fix is far more
> trivial:  simply update the "windowBits" setting in the zlib header,
> which is a single byte.  I wrote a utility to do exactly that and
> included it in the pngcheck package a decade ago; take a look and give
> it a try.  (It's a command-line tool, but as I recall, it accepts wildcard
> filenames, so
>
>         <whatever it's called> *.png
>
> should work.)

Indeed. (Just checked.) That tool is called png-fix-IDAT-windowsize.
It may or may not be packaged by your OS distribution, and, if that's
not the case, I hope you can build it from source.

Alternatively, I also noticed that pngfix (found in
libpng/contrib/tools/pngfix.c) can fix a bunch of issues, including
this one.

There is a tiny difference between pngfix and png-fix-IDAT-windowsize:
the 1st one leaves the zlib compression method at its original value;
the 2nd one sets it to "default". There is absolutely no difference in
the output image: both tools produce slightly different deflate
streams inside IDAT, but with identical output images.

Here is how to use these tools. For pngfix:

    pngfix -o --out=output.png input.png
    # produces "output.png"

And for png-fix-IDAT-windowsize:

    png-fix-IDAT-windowsize input.png
    # produces "input-fixed.png"

I hope you will be able to fix your images, Ruben.

Sincerely,
Cosmin

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