|
»
»
»
« Return to Thread: Re: APNG MIME type and extension
Re: APNG MIME type and extension
by John Bowler
::
Rate this Message:
From: Vladimir Vukicevic
>APNG is a backwards-compatible extension to PNG, as was said
It is not.
It is an incompatible extension to PNG.
It is an incompatible extension because an existing PNG application will not
even display anything remotely like the extension, let alone edit it. The
extension is an animation format, no existing PNG displaying application
displays PNGs as animations, even though many have the capability to display
animations.
It is even worse than that.
It is an incompatible extension done in an incompatible way. That is
because there are a set of rules for extending PNG such that existing
applications will not damage the extension data - even though they do not
understand it. APNG ignores this facility, the structure of APNG is such
that a non-APNG aware but completely correct application is able to damage
or totally change the APNG information in such a way that a naive APNG
implementation may be unable to reconstruct anything useful.
A great many file formats have been extended in incompatible ways in the
past, but all the cases I know of this have involved release of "version 2"
of the file format. V1 and v2 formats are typically convertible with loss
of information from v2 to v1. Application authors typically go to great
lengths to ensure that users of "v2" do not accidentally send files to "v1"
application owners without the "v1" owners being very aware of their need to
upgrade.
Backwards compatible extensions to file formats are really big deals. It is
extremely difficult to do. It is much easier to just release a new version.
It is very hard to release a new application version which writes a new file
format which is backwards compatible with the *old* applications (so that
the old apps can edit the new file format with impunity.)
APNG is not in the slightest backward compatible with PNG. It is PNG v2,
just like AGIF was GIF v2. Worse it has an almost comical similarity to
AGIF in that it seems to repeat some of the same errors in the same way.
For example like AGIF it fails to specify the precise handling of
inter-frame delay and it interprets the 'background' colour information in a
way incompatible with the base format.
It is worse than incompatible.
John Bowler <jbowler@...>
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
png-mng-misc mailing list
png-mng-misc@...
https://lists.sourceforge.net/lists/listinfo/png-mng-misc
>APNG is a backwards-compatible extension to PNG, as was said
It is not.
It is an incompatible extension to PNG.
It is an incompatible extension because an existing PNG application will not
even display anything remotely like the extension, let alone edit it. The
extension is an animation format, no existing PNG displaying application
displays PNGs as animations, even though many have the capability to display
animations.
It is even worse than that.
It is an incompatible extension done in an incompatible way. That is
because there are a set of rules for extending PNG such that existing
applications will not damage the extension data - even though they do not
understand it. APNG ignores this facility, the structure of APNG is such
that a non-APNG aware but completely correct application is able to damage
or totally change the APNG information in such a way that a naive APNG
implementation may be unable to reconstruct anything useful.
A great many file formats have been extended in incompatible ways in the
past, but all the cases I know of this have involved release of "version 2"
of the file format. V1 and v2 formats are typically convertible with loss
of information from v2 to v1. Application authors typically go to great
lengths to ensure that users of "v2" do not accidentally send files to "v1"
application owners without the "v1" owners being very aware of their need to
upgrade.
Backwards compatible extensions to file formats are really big deals. It is
extremely difficult to do. It is much easier to just release a new version.
It is very hard to release a new application version which writes a new file
format which is backwards compatible with the *old* applications (so that
the old apps can edit the new file format with impunity.)
APNG is not in the slightest backward compatible with PNG. It is PNG v2,
just like AGIF was GIF v2. Worse it has an almost comical similarity to
AGIF in that it seems to repeat some of the same errors in the same way.
For example like AGIF it fails to specify the precise handling of
inter-frame delay and it interprets the 'background' colour information in a
way incompatible with the base format.
It is worse than incompatible.
John Bowler <jbowler@...>
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
png-mng-misc mailing list
png-mng-misc@...
https://lists.sourceforge.net/lists/listinfo/png-mng-misc
« Return to Thread: Re: APNG MIME type and extension
| Free embeddable forum powered by Nabble | Forum Help |
