« Return to Thread: Re: APNG MIME type and extension
Re: APNG MIME type and extension
by glennrp-2
::
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At 10:45 PM 3/15/2007 -0700, John Bowler wrote:
>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 syntactically compatible but philosophically incompatible.
It is designed so that APNG-unaware applications will be able to
display *something*.
It is philosophically incompatible because it really contains an
animation, and the "png" signature and the "image" MIME category
both promise that it contains a still image. The proponents of
APNG are unwilling to face these facts. From the discussion that
occurred in 2004 it is evident that some of this group are willing
to ignore them.
>
>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.
I don't agree with this statement. The only thing that can happen is
that an APNG-unaware application will put the chunks out of order, which
can be detected by any APNG-aware application and fixed by an APNG-aware
editor.
>
>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.
In this case "v2" is MNG. And APNG IMO is acceptable if conveyed inside
a PNG inside a MNG.
>
>Backwards compatible extensions to file formats are really big deals. It is
>extremely difficult to do.
It is impossible to do, if the new format adds features that the spec
promises aren't there.
>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.
We can fix those technical problems.
>
>It is worse than incompatible.
>
The vote is going to be interesting, if we ever get to that point.
Glenn
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>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 syntactically compatible but philosophically incompatible.
It is designed so that APNG-unaware applications will be able to
display *something*.
It is philosophically incompatible because it really contains an
animation, and the "png" signature and the "image" MIME category
both promise that it contains a still image. The proponents of
APNG are unwilling to face these facts. From the discussion that
occurred in 2004 it is evident that some of this group are willing
to ignore them.
>
>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.
I don't agree with this statement. The only thing that can happen is
that an APNG-unaware application will put the chunks out of order, which
can be detected by any APNG-aware application and fixed by an APNG-aware
editor.
>
>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.
In this case "v2" is MNG. And APNG IMO is acceptable if conveyed inside
a PNG inside a MNG.
>
>Backwards compatible extensions to file formats are really big deals. It is
>extremely difficult to do.
It is impossible to do, if the new format adds features that the spec
promises aren't there.
>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.
We can fix those technical problems.
>
>It is worse than incompatible.
>
The vote is going to be interesting, if we ever get to that point.
Glenn
-------------------------------------------------------------------------
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Join SourceForge.net's Techsay panel and you'll get the chance to share your
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