Re: Sample-based thumbnailing built into libpng?

Glenn Randers-Pehrson <[email protected]>
Newsgroups gmane.comp.graphics.png.general
Message-ID <CA+PdXctKxyrGa-C5TF84ASnw-9Yuue1HvL7bM4TP5e87KvGJaw@mail.gmail.com>
On Thu, Jan 19, 2017 at 3:21 PM, Andrew Klaassen <clawsoon-/[email protected]> wrote:

>
> A search through this mailing list was frustrated by Sourceforge error
> messages, but I did find this previous message from 2008 that touches on
> the topic:
>
> https://sourceforge.net/p/png-mng/mailman/message/20296261/
>
> I'm not sure from that message whether it's not possible to sample
> [noninterlaced] PNG files, or whether the poster thinks that it's not
> useful because decompression is too slow to make it worthwhile.
>

The message says that it's not possible.  That fact is still true.  A PNG
decoder needs all
the preceding bytes in order to decode a row, because of how zlib
compression and
PNG filtering work.

Glenn

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