webp-container-spec: remove references to fragments
this portion of the format was never finalized
Change-Id: I80aa1b27457a0e52b047c7284df2f58b181ca5d8
diff --git a/doc/webp-container-spec.txt b/doc/webp-container-spec.txt
index b1494d0..ffcb154 100644
--- a/doc/webp-container-spec.txt
+++ b/doc/webp-container-spec.txt
@@ -46,25 +46,13 @@
* **Animation.** An image may have multiple frames with pauses between them,
making it an animation.
- * **Image Fragmentation.** A single bitstream in WebP has an inherent
- limitation for width or height of 2^14 pixels, and, when using VP8, a 512
- KiB limit on the size of the first compressed partition. To support larger
- images, the format supports images that are composed of multiple fragments,
- each encoded as a separate bitstream. All fragments logically form a single
- image: they have common metadata, color profile, etc. Image fragmentation
- may also improve efficiency for larger images, e.g., grass can be encoded
- differently than sky.
-
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119][].
**Note:** Out of the features mentioned above, lossy compression, lossless
compression, transparency, metadata, color profile and animation are finalized
-and are to be considered stable. On the other hand, image fragmentation is
-experimental as of now, and is open to discussion, feedback and comments.
-The same is indicated using annotation "_status: experimental_" in the relevant
-sections of this document.
+and are to be considered stable.
Terminology & Basics
------------------------
@@ -278,10 +266,6 @@
an _animated image_, it consists of multiple frames. More details about frames
can be found in the [Animation](#animation) section.
-Moreover, each frame can be fragmented or non-fragmented, as will be described
-in the [Extended WebP file header](#extended_header) section. More details about
-fragments can be found in the [Fragments](#fragments) section.
-
All chunks SHOULD be placed in the same order as listed above. If a chunk
appears in the wrong place, the file is invalid, but readers MAY parse the
file, ignoring the chunks that come too late.
@@ -302,7 +286,7 @@
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ChunkHeader('VP8X') |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |Rsv|I|L|E|X|A|F| Reserved |
+ |Rsv|I|L|E|X|A|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Canvas Width Minus One | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -335,9 +319,9 @@
: Set if this is an animated image. Data in 'ANIM' and 'ANMF' chunks should be
used to control the animation.
-Image Fragmentation (F): 1 bit _\[status: experimental\]_
+Reserved (R): 1 bit
-: Set if any of the frames in the image are represented by fragments.
+: SHOULD be `0`.
Reserved: 24 bits
@@ -506,9 +490,7 @@
Frame Data: _Chunk Size_ - `16` bytes
-: For a fragmented frame, it consists of multiple [fragment chunks](#fragments).
-
-: For a non-fragmented frame, it consists of:
+: Consists of:
* An optional [alpha subchunk](#alpha) for the frame.
@@ -519,49 +501,6 @@
**Note**: The 'ANMF' payload, _Frame Data_ above, consists of individual
_padded_ chunks as described by the [RIFF file format](#riff-file-format).
-#### Fragments _\[status: experimental\]_
-
-For images that are represented by fragments, this chunk contains data for
-a single fragment. If the _Image Fragmentation Flag_ is not set, then this chunk
-SHOULD NOT be present.
-
- 0 1 2 3
- 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
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | ChunkHeader('FRGM') |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Fragment X | ...
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- ... Fragment Y | Fragment Data |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
-Fragment X: 24 bits (_uint24_)
-
-: The X coordinate of the upper left corner of the fragment is `Fragment X * 2`
-
-Fragment Y: 24 bits (_uint24_)
-
-: The Y coordinate of the upper left corner of the fragment is `Fragment Y * 2`
-
-Fragment Data: _Chunk Size_ - `6` bytes
-
-: It contains:
-
- * An optional [alpha subchunk](#alpha) for the fragment.
- * The [bitstream subchunk](#bitstream-vp8vp8l) for the fragment.
- * An optional list of [unknown chunks](#unknown-chunks).
-
-Note: The width and height of the fragment is obtained from the bitstream
-subchunk.
-
-The fragments of a frame SHOULD have the following properties:
-
- * They collectively cover the whole frame.
-
- * No pair of fragments have any overlapping region on the frame.
-
- * No portion of any fragment should be located outside of the canvas.
-
#### Alpha
0 1 2 3
@@ -643,8 +582,8 @@
: Encoded alpha bitstream.
-This optional chunk contains encoded alpha data for this frame/fragment. A
-frame/fragment containing a 'VP8L' chunk SHOULD NOT contain this chunk.
+This optional chunk contains encoded alpha data for this frame. A
+frame containing a 'VP8L' chunk SHOULD NOT contain this chunk.
**Rationale**: The transparency information is already part of the 'VP8L'
chunk.
@@ -675,7 +614,7 @@
#### Bitstream (VP8/VP8L)
-This chunk contains compressed bitstream data for a single frame/fragment.
+This chunk contains compressed bitstream data for a single frame.
A bitstream chunk may be either (i) a VP8 chunk, using "VP8 " (note the
significant fourth-character space) as its tag _or_ (ii) a VP8L chunk, using
@@ -762,47 +701,17 @@
* At the end of the file as described in [Extended WebP file
header](#extended_header) section.
- * At the end of FRGM and ANMF chunks as described in [Fragments](#fragments)
- and [Animation](#animation) sections.
+ * At the end of ANMF chunks as described in the
+ [Animation](#animation) section.
Readers SHOULD ignore these chunks. Writers SHOULD preserve them in their
original order (unless they specifically intend to modify these chunks).
-### Assembling the Canvas from fragments/frames
+### Assembling the Canvas from frames
-Here we provide an overview of how a reader should assemble a canvas in case
-of a fragmented-image and in case of an animated image. The notation
-_VP8X.field_ means the field in the 'VP8X' chunk with the same description.
-
-Displaying a _fragmented image_ canvas MUST be equivalent to the following
-pseudocode: _\[status: experimental\]_
-
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-assert VP8X.flags.hasFragments
-canvas ← new black image of size VP8X.canvasWidth x VP8X.canvasHeight.
-frgm_params ← nil
-for chunk in image_data:
- assert chunk.tag is "FRGM"
- frgm_params.fragmentX = Fragment X
- frgm_params.fragmentY = Fragment Y
- for subchunk in 'Fragment Data':
- if subchunk.tag == "ALPH":
- assert alpha subchunks not found in 'Fragment Data' earlier
- frgm_params.alpha = alpha_data
- else if subchunk.tag == "VP8 " OR subchunk.tag == "VP8L":
- assert bitstream subchunks not found in 'Fragment Data' earlier
- frgm_params.bitstream = bitstream_data
- frgm_params.fragmentWidth = Width extracted from bitstream subchunk
- frgm_params.fragmentHeight = Height extracted from bitstream subchunk
- assert VP8X.canvasWidth >=
- frgm_params.fragmentX + frgm_params.fragmentWidth
- assert VP8X.canvasHeight >=
- frgm_params.fragmentY + frgm_params.fragmentHeight
- assert fragment has the properties mentioned in "Image Fragments" section.
- render fragment with frame_params.alpha and frame_params.bitstream on canvas
- with top-left corner in (frgm_params.fragmentX, frgm_params.fragmentY).
-canvas contains the decoded canvas.
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Here we provide an overview of how a reader should assemble a canvas in the
+case of an animated image. The notation _VP8X.field_ means the field in the
+'VP8X' chunk with the same description.
Displaying an _animated image_ canvas MUST be equivalent to the following
pseudocode:
@@ -825,20 +734,13 @@
frame_params.frameDuration = Frame Duration
assert VP8X.canvasWidth >= frame_params.frameX + frame_params.frameWidth
assert VP8X.canvasHeight >= frame_params.frameY + frame_params.frameHeight
- if VP8X.flags.hasFragments and first subchunk in 'Frame Data' is FRGM
- // Fragmented frame.
- frame_params.{bitstream,alpha} = canvas decoded from subchunks in
- 'Frame Data' as per the pseudocode for
- _fragmented image_ above.
- else
- // Non-fragmented frame.
- for subchunk in 'Frame Data':
- if subchunk.tag == "ALPH":
- assert alpha subchunks not found in 'Frame Data' earlier
- frame_params.alpha = alpha_data
- else if subchunk.tag == "VP8 " OR subchunk.tag == "VP8L":
- assert bitstream subchunks not found in 'Frame Data' earlier
- frame_params.bitstream = bitstream_data
+ for subchunk in 'Frame Data':
+ if subchunk.tag == "ALPH":
+ assert alpha subchunks not found in 'Frame Data' earlier
+ frame_params.alpha = alpha_data
+ else if subchunk.tag == "VP8 " OR subchunk.tag == "VP8L":
+ assert bitstream subchunks not found in 'Frame Data' earlier
+ frame_params.bitstream = bitstream_data
render frame with frame_params.alpha and frame_params.bitstream on canvas
with top-left corner in (frame_params.frameX, frame_params.frameY), using
dispose method dispose_method.
@@ -878,17 +780,6 @@
+- XMP (metadata)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-A fragmented image may look as follows:
-
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-RIFF/WEBP
-+- VP8X (descriptions of features used)
-+- FRGM (fragment1 parameters + data)
-+- FRGM (fragment2 parameters + data)
-+- FRGM (fragment3 parameters + data)
-+- FRGM (fragment4 parameters + data)
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
An animated image with EXIF metadata may look as follows:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
