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WebP Container:
annotate specific sections as experimental Change-Id: If43222cef1c4fc2a8164b5f6ca4e89033379757d
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Urvang Joshi
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@ -13,9 +13,6 @@ end of this file.
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WebP Container Specification
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============================
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_Working Draft, v1.0, 20121109_
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* TOC placeholder
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{:toc}
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@ -62,6 +59,12 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC 2119][].
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**Note:** Out of the features mentioned above, lossy compression, lossless
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compression and transparency are finalized and are to be considered stable.
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On the other hand, metadata, color profile, animation and image fragmentation
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are experimental as of now, and are open to discussion, feedback and comments.
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The same is indicated using annotation "_status: experimental_" in the relevant
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sections of this document.
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Terminology & Basics
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------------------------
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@ -271,17 +274,17 @@ An extended format file consists of:
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* A 'VP8X' chunk with information about features used in the file.
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* An optional 'ICCP' chunk with color profile.
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* An optional 'ICCP' chunk with color profile. _\[status: experimental\]_
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* An optional 'ANIM' chunk with animation control data.
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* An optional 'ANIM' chunk with animation control data. _\[status: experimental\]_
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* Image data.
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* An optional 'EXIF' chunk with EXIF metadata.
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* An optional 'EXIF' chunk with EXIF metadata. _\[status: experimental\]_
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* An optional 'XMP ' chunk with XMP metadata.
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* An optional 'XMP ' chunk with XMP metadata. _\[status: experimental\]_
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* An optional list of [unknown chunks](#unknown-chunks).
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* An optional list of [unknown chunks](#unknown-chunks). _\[status: experimental\]_
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For a _still image_, the _image data_ consists of a single frame, whereas for
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an _animated image_, it consists of multiple frames. More details about frames
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@ -322,7 +325,7 @@ Reserved (Rsv): 2 bits
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: SHOULD be `0`.
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ICC profile (I): 1 bit
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ICC profile (I): 1 bit _\[status: experimental\]_
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: Set if the file contains an ICC profile.
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@ -331,20 +334,20 @@ Alpha (L): 1 bit
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: Set if any of the frames of the image contain transparency information
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("alpha").
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EXIF metadata (E): 1 bit
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EXIF metadata (E): 1 bit _\[status: experimental\]_
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: Set if the file contains EXIF metadata.
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XMP metadata (X): 1 bit
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XMP metadata (X): 1 bit _\[status: experimental\]_
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: Set if the file contains XMP metadata.
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Animation (A): 1 bit
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Animation (A): 1 bit _\[status: experimental\]_
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: Set if this is an animated image. Data in 'ANIM' and 'ANMF' chunks should be
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used to control the animation.
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Image Fragmentation (F): 1 bit
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Image Fragmentation (F): 1 bit _\[status: experimental\]_
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: Set if any of the frames in the image are represented by fragments.
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@ -368,7 +371,7 @@ Future specifications MAY add more fields.
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### Chunks
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#### Animation
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#### Animation _\[status: experimental\]_
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An animation is controlled by ANIM and ANMF chunks.
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@ -475,7 +478,7 @@ Frame Data: _Chunk Size_ - `16` bytes
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* An optional list of [unknown chunks](#unknown-chunks).
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#### Fragments
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#### Fragments _\[status: experimental\]_
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For images that are represented by fragments, this chunk contains data for
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a single fragment. If the _Image Fragmentation Flag_ is not set, then this chunk
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@ -641,7 +644,7 @@ The formats of VP8 and VP8L chunks are as described in sections
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[Simple file format (lossy)](#simple-file-format-lossy)
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and [Simple file format (lossless)](#simple-file-format-lossless) respectively.
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#### Color profile
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#### Color profile _\[status: experimental\]_
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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@ -663,7 +666,7 @@ See the [ICC Specification][iccspec] for details.
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If this chunk is not present, sRGB SHOULD be assumed.
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#### Metadata
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#### Metadata _\[status: experimental\]_
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Metadata can be stored in 'EXIF' or 'XMP ' chunks.
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@ -705,7 +708,7 @@ XMP Metadata: _Chunk Size_ bytes
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Additional guidance about handling metadata can be found in the
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Metadata Working Group's [Guidelines for Handling Metadata][metadata].
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#### Unknown Chunks
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#### Unknown Chunks _\[status: experimental\]_
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A RIFF chunk (described in [this](#terminology-amp-basics) section) whose _chunk
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tag_ is different from any of the chunks described in this document, is
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@ -724,7 +727,7 @@ A file MAY contain unknown chunks:
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Readers SHOULD ignore these chunks. Writers SHOULD preserve them in their
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original order (unless they specifically intend to modify these chunks).
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### Assembling the Canvas from fragments/frames
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### Assembling the Canvas from fragments/frames _\[status: experimental\]_
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Here we provide an overview of how a reader should assemble a canvas in case
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of a fragmented-image and in case of an animated image. The notation
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