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"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 orderwith the range 0 to (2^16)-1; a "byte" shall be an 8-bit unsigned integerwith the range 0 to (2^8)-1.
== Error Handling ==
Sequence number Chunk
(none) `acTL` 0 `fcTL` first frame (before none) `IDAT`)first frame / default image
1 `fcTL` second frame
2 first `fdAT` for second frame
Sequence number Chunk
(none) `acTL`
(none) `IDAT` default image
0 `fcTL` first frame
1 first `fdAT` for first frame
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 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.
[pngspec]: http://www.w3.org/TR/PNG/ "Portable Network Graphics (PNG) Specification (Second Edition)"
[pngext]: http://wwwpmt.libpngsourceforge.orgnet/pubspecs/png/spec/register/pngext-1.2.0-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"
