APNG Specification - Revision history

Tantek: note main metabug

2025-05-29T21:53:27Z

note main metabug

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	{{note\|Please see the [https://www.w3.org/TR/png-3/ PNG 3e specification] at W3C which has incorporated the APNG Specification}}		{{note\|Please see the [https://www.w3.org/TR/png-3/ PNG 3e specification] at W3C which has incorporated the APNG Specification}}
			Main meta-bug:
			* [https://bugzilla.mozilla.org/show_bug.cgi?id=495609 495609: Implement PNG Third Edition (incorporated prior APNG spec)]
	{{historical}}		{{historical}}

Tantek: historical page, see W3C spec

2025-05-22T00:39:56Z

historical page, see W3C spec

← Older revision		Revision as of 00:39, 22 May 2025
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			{{note\|Please see the [https://www.w3.org/TR/png-3/ PNG 3e specification] at W3C which has incorporated the APNG Specification}}

			{{historical}}

	APNG 1.0		APNG 1.0

Annevk: Mention the image/apng MIME type

2015-09-26T10:02:54Z

Mention the image/apng MIME type

← Older revision		Revision as of 10:02, 26 September 2015
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	If the PNG `pHYs` chunk is present, the APNG images and their `x_offset` and `y_offset` values must be scaled in the same way as the main image. Conceptually, such scaling occurs while mapping the output buffer onto the canvas.		If the PNG `pHYs` chunk is present, the APNG images and their `x_offset` and `y_offset` values must be scaled in the same way as the main image. Conceptually, such scaling occurs while mapping the output buffer onto the canvas.

			= MIME type =

			APNG can be identified using the <code>image/apng</code> MIME type.

	= Revisions to this Specification =		= Revisions to this Specification =

Jwein: /* `fcTL`: The Frame Control Chunk */

2012-06-01T18:07:07Z

`fcTL`: The Frame Control Chunk

← Older revision		Revision as of 18:07, 1 June 2012
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	As noted earlier, the output buffer must be completely initialized to fully transparent black at the beginning of each play. This is to ensure that each play of the animation will be identical. Decoders are free to avoid an explicit clear step as long as the result is guaranteed to be identical. For example, if the default image is included in the animation, and uses a `blend_op` of APNG_BLEND_OP_SOURCE, clearing is not necessary because the entire output buffer will be overwritten.		As noted earlier, the output buffer must be completely initialized to fully transparent black at the beginning of each play. This is to ensure that each play of the animation will be identical. Decoders are free to avoid an explicit clear step as long as the result is guaranteed to be identical. For example, if the default image is included in the animation, and uses a `blend_op` of APNG_BLEND_OP_SOURCE, clearing is not necessary because the entire output buffer will be overwritten.

			Note, at the end of the fcTL chunk is a 32-bit CRC checksum. The checksum is calculated using the fcTL chunk and includes the 'fcTL' bytes.

	== `fdAT`: The Frame Data Chunk ==		== `fdAT`: The Frame Data Chunk ==

Tantek: add link to tests from Philip

2010-06-09T23:05:26Z

add link to tests from Philip

← Older revision		Revision as of 23:05, 9 June 2010
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	*http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"		*http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"
	*http://www.animatedpng.com "APNG Project - official Site"		*http://www.animatedpng.com "APNG Project - official Site"

			= B. Tests =
			* http://philip.html5.org/tests/apng/tests.html

Andrew at 23:08, 24 March 2010

2010-03-24T23:08:07Z

← Older revision		Revision as of 23:08, 24 March 2010
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	* Stuart Parmenter <pavlov@pavlov.net>		* Stuart Parmenter <pavlov@pavlov.net>
	* Vladimir Vukicevic <vladimir@pobox.com>		* Vladimir Vukicevic <vladimir@pobox.com>
	* Andrew Smith <~~asmith15~~@littlesvr.ca>		* Andrew Smith <asmith16@littlesvr.ca>

	= Overview =		= Overview =

Pabouk: corrected links and a typo

2008-08-14T10:13:54Z

corrected links and a typo

← Older revision		Revision as of 10:13, 14 August 2008
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	= Overview =		= Overview =

	APNG is an extension of the [PNG~~][pngspec~~] format, adding support for animated images. It is intended to be a replacement for simple animated images that have traditionally used the [GIF~~][gifspec~~] format, while adding support for 24-bit images and 8-bit transparency. APNG is a simpler alternative to MNG, providing a spec suitable for the most common usage of animated images on the Internet.		APNG is an extension of the [http://www.w3.org/TR/PNG/ PNG] format, adding support for animated images. It is intended to be a replacement for simple animated images that have traditionally used the [http://www.w3.org/Graphics/GIF/spec-gif89a.txt GIF] format, while adding support for 24-bit images and 8-bit transparency. APNG is a simpler alternative to MNG, providing a spec suitable for the most common usage of animated images on the Internet.

	APNG is backwards-compatible with PNG; any PNG decoder should be able to ignore the APNG-specific chunks and display a single image.		APNG is backwards-compatible with PNG; any PNG decoder should be able to ignore the APNG-specific chunks and display a single image.
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	The "default image" is the image described by the standard `IDAT` chunks, and is the image that is displayed by decoders that do not support APNG.		The "default image" is the image described by the standard `IDAT` chunks, and is the image that is displayed by decoders that do not support APNG.

	The "canvas" is the area on the output device on which the frames are to be displayed. The contents of the canvas are not necessarily available to the decoder. As per the PNG Specification, if a `bKGD` chunk exists it may be used to fill the canvas if there is no ~~preferrable~~ background.		The "canvas" is the area on the output device on which the frames are to be displayed. The contents of the canvas are not necessarily available to the decoder. As per the PNG Specification, if a `bKGD` chunk exists it may be used to fill the canvas if there is no preferable background.

	The "output buffer" is a pixel array with dimensions specified by the width and height parameters of the PNG `IHDR` chunk. Conceptually, each frame is constructed in the output buffer before being composited onto the canvas. The contents of the output buffer are available to the decoder. The corners of the output buffer are mapped to the corners of the canvas.		The "output buffer" is a pixel array with dimensions specified by the width and height parameters of the PNG `IHDR` chunk. Conceptually, each frame is constructed in the output buffer before being composited onto the canvas. The contents of the output buffer are available to the decoder. The corners of the output buffer are mapped to the corners of the canvas.
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	= Structure =		= Structure =

	An APNG stream is a normal PNG stream as defined in the [PNG Specification~~][pngspec~~], with three additional chunk types describing the animation and providing additional frame data.		An APNG stream is a normal PNG stream as defined in the [http://www.w3.org/TR/PNG/ PNG Specification], with three additional chunk types describing the animation and providing additional frame data.

	To be recognized as an APNG, an `acTL` chunk must appear in the stream before any `IDAT` chunks. The `acTL` structure is described below.		To be recognized as an APNG, an `acTL` chunk must appear in the stream before any `IDAT` chunks. The `acTL` structure is described below.
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	= Test Encoder and Sample Images =		= Test Encoder and Sample Images =

	Sample images are available from the APNG implementation page at http://littlesvr.ca/apng/		*Sample images are available from the APNG implementation page at http://littlesvr.ca/apng/
			*An encoder (open source) is available in Mozilla versions newer than alpha 4.
	An encoder (open source) is available in Mozilla versions newer than alpha 4.		*An application (open source) using the Mozilla encoder to assemble APNGs available here: http://littlesvr.ca/apng/apngedit.html

	An application (open source) using the Mozilla encoder to assemble APNGs available here: http://littlesvr.ca/apng/apngedit.html

	= A. References =		= A. References =

	~~[pngspec]:~~ http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"		*http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"
			*http://pmt.sourceforge.net/specs/png-1.2-pdg.html "Extensions to the PNG Specification, Version 1.2.0"
	~~[pngext]:~~ http://pmt.sourceforge.net/specs/png-1.2-pdg.html "Extensions to the PNG Specification, Version 1.2.0"		*http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"
			*http://www.animatedpng.com "APNG Project - official Site"
	~~[gifspec]:~~ http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"

	~~[pngproject]:~~ http://www.animatedpng.com "APNG Project - official Site"

BrotherBrendan: /* A. References */

2008-01-28T06:46:47Z

A. References

← Older revision		Revision as of 06:46, 28 January 2008
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	[gifspec]: http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"		[gifspec]: http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"

			[pngproject]: http://www.animatedpng.com "APNG Project - official Site"

Andrew at 07:20, 24 September 2007

2007-09-24T07:20:16Z

← Older revision		Revision as of 07:20, 24 September 2007
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	"Fully transparent black" means red, green, blue and alpha components are all set to zero.		"Fully transparent black" means red, green, blue and alpha components are all set to zero.

	For purposes of chunk descriptions, an "unsigned int" shall be a 32-bit unsigned integer in network byte order limited to the range 0 to (2^31)-1; an "unsigned short" shall be a 16-bit unsigned integer in network byte order; a "byte" shall be an 8-bit unsigned integer.		For purposes of chunk descriptions, an "unsigned int" shall be a 32-bit unsigned integer in network byte order limited to the range 0 to (2^31)-1; an "unsigned short" shall be a 16-bit unsigned integer in network byte order with the range 0 to (2^16)-1; a "byte" shall be an 8-bit unsigned integer with the range 0 to (2^8)-1.

	== Error Handling ==		== Error Handling ==
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	Sequence number Chunk		Sequence number Chunk
	0 `fcTL` first frame (~~before~~ `IDAT`)		(none) `acTL`
			0 `fcTL` first frame
			(none) `IDAT` first frame / default image
	1 `fcTL` second frame		1 `fcTL` second frame
	2 first `fdAT` for second frame		2 first `fdAT` for second frame
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	Sequence number Chunk		Sequence number Chunk
			(none) `acTL`
			(none) `IDAT` default image
	0 `fcTL` first frame		0 `fcTL` first frame
	1 first `fdAT` for first frame		1 first `fdAT` for first frame
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	1 APNG_BLEND_OP_OVER		1 APNG_BLEND_OP_OVER

	If `blend_op` is APNG_BLEND_OP_SOURCE all color components of the frame, including alpha, overwrite the current contents of the frame's output buffer region. If `blend_op` is APNG_BLEND_OP_OVER the frame should be composited onto the output buffer based on its alpha, using a simple OVER operation as described in the "Alpha Channel Processing" section of the PNG specification [PNG-1.2]. Note that ~~Variation 2~~ of the sample code is applicable.		If `blend_op` is APNG_BLEND_OP_SOURCE all color components of the frame, including alpha, overwrite the current contents of the frame's output buffer region. If `blend_op` is APNG_BLEND_OP_OVER the frame should be composited onto the output buffer based on its alpha, using a simple OVER operation as described in the "Alpha Channel Processing" section of the PNG specification [PNG-1.2]. Note that the second variation of the sample code is applicable.

	Note that for the first frame the two blend modes are functionally equivalent due to the clearing of the output buffer at the beginning of each play.		Note that for the first frame the two blend modes are functionally equivalent due to the clearing of the output buffer at the beginning of each play.
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	[pngspec]: http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"		[pngspec]: http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"
	* http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"

	[pngext]: http://~~www~~.~~libpng~~.~~org~~/~~pub~~/png~~/spec/register/pngext~~-1.2~~.0-pdg.html "Extensions to the PNG Specification, Version 1.2.0"~~		[pngext]: http://pmt.sourceforge.net/specs/png-1.2-pdg.html "Extensions to the PNG Specification, Version 1.2.0"
	* http://www.libpng.org/pub/png/spec/register/pngext-1.2.0-pdg.html "Extensions to the PNG Specification, Version 1.2.0"

	[gifspec]: http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"		[gifspec]: http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"
	* http://www.w3.org/Graphics/GIF/spec-gif89a.txt "Graphics Interchange Format 89a"

Andrew at 21:43, 20 September 2007

2007-09-20T21:43:14Z

← Older revision		Revision as of 21:43, 20 September 2007
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	* Stuart Parmenter <pavlov@pavlov.net>		* Stuart Parmenter <pavlov@pavlov.net>
	* Vladimir Vukicevic <vladimir@pobox.com>		* Vladimir Vukicevic <vladimir@pobox.com>
	* Andrew Smith <asmith15@~~learn.senecac.on~~.ca>		* Andrew Smith <asmith15@littlesvr.ca>

	= Overview =		= Overview =