APNG

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Short description: File format
Animated Portable Network Graphics
Animated PNG example bouncing beach ball.png
An animated PNG, or APNG, of a bouncing ball (displays as static image in some web browsers)
Filename extension.png .apng
Initial releaseAugust 4, 2008; 15 years ago (2008-08-04)
Type of formatanimated raster image format
Extended fromPNG

Animated Portable Network Graphics (APNG) is a file format which extends the Portable Network Graphics (PNG) specification to permit animated images that work similarly to animated GIF files, while supporting 24-bit images and 8-bit transparency not available for GIFs. It also retains backward compatibility with non-animated PNG files.

The first frame of an APNG file is stored as a normal PNG stream, so most standard PNG decoders are able to display the first frame of an APNG file. The frame speed data and extra animation frames are stored in extra chunks (as provided for by the original PNG specification). APNG competed with Multiple-image Network Graphics (MNG), a comprehensive format for bitmapped animations which was created by the same team as PNG and is obsolete. APNG's advantage was the smaller library size and compatibility with older PNG implementations.

In a comparison made between GIF, APNG and lossless WebP, APNG had the lowest file size.[1]

History

An APNG of an MRI scan of a human head

The APNG specification was created in 2004 by Stuart Parmenter and Vladimir Vukićević of the Mozilla Corporation to allow for storing the animations needed for interfaces such as throbbers. In May 2003, Mozilla had scrapped support for MNG animations, which provides a superset of APNG functionality, citing concerns about the large file size required for the expansive MNG decoder library (300 KB);[2] the APNG decoder, built on the back of the PNG decoder, was a much smaller component.

Among users and maintainers of the PNG and MNG formats, APNG had a lukewarm reception. In particular, PNG was conceived to be a single-image format.[3] APNG hides the subsequent frames in PNG ancillary chunks in such a way that APNG-unaware applications would ignore them, but there are otherwise no changes to the format to allow software to distinguish between animated and non-animated images. Some of the main concerns arising from this were the inability of applications to negotiate for PNG and APNG, or distinguish between PNG and APNG once received, or for legacy software to even inform users that there are additional frames. Glenn Randers-Pehrson spearheaded efforts to reconcile the PNG purists' position with that of APNG proponents by recommending changes to APNG's format and proposing the use of a unique MIME type (e.g., video/png), but the APNG proponents only added the different MIME type (image/apng)[4] while insisting on the use of the .png extension instead of .apng, leading to the format not being approved by the PNG Development Group.[5]

The PNG group officially rejected APNG as an official extension on April 20, 2007.[6] There have been several subsequent proposals for a simple animated graphics format based on PNG using several different approaches.[7]

Mozilla Firefox added support for APNG in version 3 trunk builds on March 23, 2007.[8] However, because libpng is the PNG Group's reference implementation of the official specification, APNG support can never be supported in the main libpng distribution so long as it remains unratified by the Group. Iceweasel 3 supports APNG by using Mozilla's unofficial variant of libpng.[9]

The logo of APNG Assembler, free software to create APNG images

In 2008 WorldDMB adopted APNG as a backward compatible extension to enable animation as part of the MOT SlideShow user application for Digital Radio. "APNG 1.0 Specification - Animated Portable Network Graphics" is included as normative Annex A in the ETSI standard TS 101 499 V2.2.1.[10] In 2010 Commercial Radio Broadcasters in Sydney began to include APNG animations in DAB+ digital radio broadcasts.[citation needed] These APNG animations are carried by the "MOT slideshow" application which accompanies the audio services. It is expected that other cities in Australia will follow in early 2011.[citation needed][needs update]

Mozilla's role in extending the PNG format to APNG echoes Netscape's much earlier role in popularizing animated GIFs.[citation needed]

In 2016, Apple adopted the APNG format as the preferred format for animated stickers in iOS 10 iMessage apps.[11]

On March 15, 2017, APNG support was added to Chromium.[12]

File format

The APNG specification follows the PNG File format introducing three new ancillary chunks:[13]

  • The animation control chunk (acTL) precedes the IDAT(s) of the default image and is a kind of "marker" that this is an animated PNG file. It also contains the number of frames and the number of times to loop the animation (0 meaning infinite).
  • The frame control chunk (fcTL) precedes each frame and contains its metadata : dimensions; position (relative to the default image); duration; if once over it is cleared to black, replaced by the previous frame or drawn over by the next frame; and if its transparency applies.
  • The frame data chunk (fdAT) storing frame's content. It starts with a sequence number, then has the same structure as the default image's IDAT chunk(s).

Sequence numbers apply to both frame control and frame data chunks, which together follow a common sequence, thus enabling the order and timing of frames to be recovered should an APNG-unaware PNG editor re-order them as allowed by PNG chunk ordering rules.[14]

Frames utilize the same bit depth, color type, compression method, filter method, interlace method, and palette (if any) as the default image.

An application reading a PNG file is meant to ignore any chunks which it does not understand,[15] making APNG backwards compatible. Applications without support for the APNG extension show only the first frame, disregarding additional animation frames.

Diagram illustrating a possible way to assemble an animated PNG from three individual PNG files

Compression and Optimization

A number of optimization techniques make APNG files as small as possible: Inter-frame optimization [16] utilizing alpha-blend and alpha dispose operations, smaller than the full-size subframes, dirty transparency, color type and color palette optimizations, and various compression options: zlib, 7-Zip, Zopfli.[17]

Derived formats

Animated stickers for Signal are APNG with some restrictions.[which?][18]

Support

List of computer programs and their support of APNG, along with their version numbers and release date
Field Software Supports? Since
Image
processing 		APNG Assembler Yes v. 1[19]
cphktool APNG Anime Maker Yes v. 1 (9 June 2009)[20]
APNG Disassembler Yes v. 1 [21]
APNG Optimizer Yes v. 1.0 (28 March 2011)[22]
Chasys Draw IES Yes[23] v. 5.17.05[24]
FFmpeg Yes[25] v. 2.7[26]
Yes v. 2.3.13[27]
Gamani GIF Movie Gear Yes v. 4.2 (March 2008)[28]
GID Read-only v. 11 (December 2023)[29]
GIMP Needs plug-in[30] N/A
Honeycam Yes v. 3.48 (29 November 2021)[31]
Honeyview Yes v. 5.10 (17 February 2015)[32]
ImageJ Yes v. 1.41g (3 July 2008)[33]
ImageMagick Yes v. 7.0.10-31 (20 September 2020)[34]
Imagine Yes v. 1.0.2 (4 May 2008)[35]
IrfanView Read-only v. 4.40 (31 July 2015)
Konvertor Yes v. 4.02 (May 2010)[36]
KSquirrel (later SAIL) Read-only v. 0.7.2 (3 October 2007)[37]
Paint.NET Needs plugin[38] N/A
RealWorld Paint Yes v. 2011.1 (December 2011)[39]
VirtualDub Needs plugin[40][lower-alpha 1] N/A
XnView Read-only v. 1.97.4 (30 April 2010)[41]
Sciter and HTMLayout UI engines Read-only since 2008
Krita Yes[42] Krita Nightly 5.0.0 pre-alpha (since 22 February 2021)[43]
qView Read-only v. 4.0 (31 October 2020)
Browser
engines 		WebKit Yes (17 March 2015)[44]
Blink Yes June 2017
Web
browsers 		Mozilla Firefox
(Gecko layout engine) 		Yes v. 3 (17 June 2008)[45][46]
SeaMonkey
(Gecko layout engine) 		Yes v. 2
Iceweasel and other Debian rebrandings
(Gecko layout engine) 		Yes v. 4.0~b12[9]
Safari
(WebKit layout engine) 		Yes v. 8.0[47]
Google Chrome and Chromium
(Blink layout engine) 		Yes v. 59 (5 June 2017)[48][49]
Internet Explorer
(Trident layout engine) 		No[47] N/A
Microsoft Edge
(EdgeHTML layout engine) 		No[47][50] N/A
Microsoft Edge
(Blink layout engine) 		Yes v. 79
Opera v12 and earlier
(Presto layout engine) 		Yes v. 9.5 (12 June 2008)[51]
Opera 15 and later
(Blink layout engine) 		Yes v. 46.0 (22 June 2017)[52]
Pale Moon (Goanna layout engine) Yes v. 27
Mobile
browsers 		iOS Safari Yes[47] v. 8.0
Firefox for Android Yes[47] ?
Samsung Internet for Android Yes v. 7.0
Opera Mobile ?
Productivity
software 		LibreOffice Yes[53] Planned
  1. ↑ After loading a video, an APNG file can be created via the "File|Export|Animated PNG" menu item.

A server-side library exists that allows web browsers that support the canvas tag, but do not support APNG, to display APNGs.[54] Examples of such browsers include Microsoft Edge and Internet Explorer 9.

See also

References

  1. ↑ "GIF vs APNG vs WebP". littlesvr. http://littlesvr.ca/apng/gif_apng_webp.html. 
  2. ↑ martin (1999-11-11). "Bug 18574 - (mng) restore support for MNG animation format and JNG image format". Mozilla. https://bugzilla.mozilla.org/show_bug.cgi?id=18574#c72. 
  3. ↑ "PNG (Portable Network Graphics) Specification, Version 1.1#8.4. Multiple-image extension". libpng. http://www.libpng.org/pub/png/spec/1.1/PNG-Misc.html#Multiple-image-extension. 
  4. ↑ "APNG Specification, Version 1.0#MIME type". Mozilla. https://wiki.mozilla.org/APNG_Specification#MIME_type. 
  5. ↑ "ImageMagick can't detect animated PNG". https://github.com/ImageMagick/ImageMagick/issues/24#issuecomment-136362187. 
  6. ↑ "VOTE FAILED: APNG 20070405a". SourceForge mailing list. 2007-04-20. http://sourceforge.net/mailarchive/message.php?msg_id=131482. 
  7. ↑ "Discussion for a simple "animated" PNG format". http://gjuyn.xs4all.nl/pnganim.html. 
  8. ↑ "Gran Paradiso Alpha 3 release notes". Mozilla. 2007-03-23. https://www.mozilla.org/projects/firefox/3.0a3/releasenotes/. 
  9. ↑ 9.0 9.1 "Debian Bug #486827 Iceweasel cannot render APNG image". Debian. 2011-08-26. http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=486827#43. 
  10. ↑ "Digital Audio Broadcasting (DAB); MOT SlideShow; User Application (pdf) Specification". ETSI. http://www.etsi.org/deliver/etsi_ts/101400_101499/101499/02.02.01_60/ts_101499v020201p.pdf. 
  11. ↑ Inc., Apple. "Messaging - Extensions - iOS Human Interface Guidelines". https://developer.apple.com/ios/human-interface-guidelines/extensions/messaging/. 
  12. ↑ "Anzwix / Chromium / Add support for Animated PNG". http://anzwix.com/a/Chromium/Add%20Support%20For%20Animated%20PNG. 
  13. ↑ "APNG Specification - MozillaWiki". https://wiki.mozilla.org/APNG_Specification. 
  14. ↑ Chunk Ordering Rules (PNG 1.2 spec)
  15. ↑ "Portable Network Graphics (PNG) Specification (Second Edition)". http://www.w3.org/TR/PNG/. 
  16. ↑ "Inter-frame Optimization in APNG". http://littlesvr.ca/apng/inter-frame.html. 
  17. ↑ "APNG Assembler". http://apngasm.sourceforge.net/. 
  18. ↑ "Stickers" (in en). Signal. https://support.signal.org/hc/en-us/articles/360031836512-Stickers#sticker_reqs. 
  19. ↑ maxst. "APNG Assembler". https://sourceforge.net/projects/apngasm/. 
  20. ↑ "cphktool APNG Anime Maker". cphktool. http://sites.google.com/site/cphktool/apng-anime-maker. 
  21. ↑ maxst. "APNG Disassembler". http://apngdis.sourceforge.net/. 
  22. ↑ maxst. "APNG Optimizer". https://sourceforge.net/projects/apng/files/APNG_Optimizer/. 
  23. ↑ "Online Help for Chasys Draw IES: File Formats - Other Image Files". https://www.jpchacha.com/chasysdraw/help.php?file=files_image.htm. 
  24. ↑ "Online Help for Chasys Draw IES: History". https://www.jpchacha.com/chasysdraw/help.php?file=history.htm#changelog. 
  25. ↑ "FFmpeg Formats Documentation". https://www.ffmpeg.org/ffmpeg-formats.html#apng. 
  26. ↑ "GitHub changelog of FFmpeg". https://github.com/FFmpeg/FFmpeg/blob/master/Changelog. 
  27. ↑ "FireAlpaca Update History". https://firealpaca.com/download/#history. 
  28. ↑ "Animated PNG: Simple Animation with an Alpha Channel". Gamani. http://www.gamani.com/apng.htm. 
  29. ↑ "GID (Generic Image Decoder)". https://github.com/zertovitch/gid. 
  30. ↑ "APNG Plug-In". http://registry.gimp.org/node/24394. 
  31. ↑ "Honeycam - Version history". Bandisoft International Inc.. https://www.bandisoft.com/honeycam/history/. 
  32. ↑ "Honeyview - Version history". Bandisoft International Inc.. https://www.bandisoft.com/honeyview/history/. 
  33. ↑ "ImageJ News". ImageJ. http://rsb.info.nih.gov/ij/notes.html. 
  34. ↑ "ImageMagick - Changelog". https://imagemagick.org/script/changelog.php. Retrieved 2021-04-25. 
  35. ↑ "Imagine - What's new". http://nyam.pe.kr/dev/imagine/doc/Whatsnew.txt. 
  36. ↑ "Konvertor - Solutions for Multimedia Processing". http://www.konvertor.net/indexe.html. 
  37. ↑ "KSquirrel Codecs ChangeLog". 15 October 2021. https://github.com/smoked-herring/sail/blob/master/CHANGELOG.md. 
  38. ↑ "Animated Image 2.4 - AGIF & APNG". http://forums.getpaint.net/index.php?/topic/13454-animated-image-24-agif-apng/. 
  39. ↑ "More about animated PNG - Vlasta's blog". http://www.rw-designer.com/entry/390. 
  40. ↑ "SourceForge.net: VirtualDub APNG Mod". https://vdubapngmod.sourceforge.net/. 
  41. ↑ While XnView is available for several operating systems, only versions for Windows have been released since APNG support was added.
  42. ↑ "APNG export support". https://bugs.kde.org/show_bug.cgi?id=342479. 
  43. ↑ "APNG and WEBP animation export (dbe993da) · Commits · Graphics / Krita" (in en). https://invent.kde.org/graphics/krita/-/commit/dbe993da3d369fc850553173ba55a3d2c8981917. 
  44. ↑ "Animated PNG graphics". WebKit. Mar 17, 2015. http://trac.webkit.org/changeset/181632. 
  45. ↑ Parmenter, Stuart; Vladimir Vukicevic; Andrew Smith (July 4, 2008). "Animated PNG graphics". Mozilla. https://developer.mozilla.org/en/Animated_PNG_graphics. 
  46. ↑ "Firefox 3 for developers". Mozilla. October 1, 2008. https://developer.mozilla.org/en/Firefox_3_for_developers. 
  47. ↑ 47.0 47.1 47.2 47.3 47.4 "Animated PNG (APNG)". http://caniuse.com/#feat=apng. 
  48. ↑ "7d2b8c45afc9c0230410011293cc2e1dbb8943a7 - chromium/src - Git at Google". https://chromium.googlesource.com/chromium/src/+/7d2b8c45afc9c0230410011293cc2e1dbb8943a7. 
  49. ↑ "Stable Channel Update for Desktop" (in en-US). Chrome Releases. https://chromereleases.googleblog.com/2017/06/stable-channel-update-for-desktop.html. 
  50. ↑ "The status of APNG image format in Microsoft Edge". https://developer.microsoft.com/en-us/microsoft-edge/platform/status/apngimageformat/. 
  51. ↑ "Web specifications supported in Opera 9.5". Opera Software. http://www.opera.com/docs/specs/opera95/#graphics. 
  52. ↑ "Opera 46 goes final, more quality and Opera's first TV ad". Opera Software. 22 June 2017. http://blogs.opera.com/desktop/2017/06/opera-46-goes-final-more-quality-and-operas-first-tv-ad/. 
  53. ↑ "Projects selected for LibreOffice in the Google Summer of Code 2023: Add APNG import/export support". LibreOffice. 29 May 2023. https://blog.documentfoundation.org/blog/2023/05/29/projects-selected-for-libreoffice-in-the-google-summer-of-code-2023/. 
  54. ↑ "APNG-canvas Library". 11 October 2021. https://github.com/davidmz/apng-canvas. 

External links



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