Issue 241 in webp: Incorrect flag details in WebP file header documentation?

[we...@googlecode.com]

Status: New
Owner: ----
Labels: Type-Defect Priority-Medium

New issue 241 by drewnoakes: Incorrect flag details in WebP file header
documentation?
https://code.google.com/p/webp/issues/detail?id=241

The documentation of the WebP container format here:

https://developers.google.com/speed/webp/docs/riff_container#extended_file_format

Shows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WebP file header (12 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ChunkHeader('VP8X') |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Rsv|I|L|E|X|A|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Canvas Width Minus One | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Canvas Height Minus One |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where the flags are:

I: ICC profile
L: Alpha
E: EXIF metadata
X: XMP metadata
A: Animation

However the project source code shows (in mux_types.h):

// VP8X Feature Flags.
typedef enum WebPFeatureFlags {
FRAGMENTS_FLAG = 0x00000001,
ANIMATION_FLAG = 0x00000002,
XMP_FLAG = 0x00000004,
EXIF_FLAG = 0x00000008,
ALPHA_FLAG = 0x00000010,
ICCP_FLAG = 0x00000020
} WebPFeatureFlags;

Does this differ across versions of the file format, or am I
misunderstanding the documentation?

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[we...@googlecode.com]

Comment #1 on issue 241 by jz...@google.com: Incorrect flag details in WebP

file header documentation?
https://code.google.com/p/webp/issues/detail?id=241

The bits in the image are in MSB order -- with the numbering starting
at '0' for the high order bit. This is pretty common in RFC(-like)
documents, but I don't think that's mentioned explicitly. The doc could use
an update.

[we...@googlecode.com]

Updates:
Status: Started

Comment #2 on issue 241 by jz...@google.com: Incorrect flag details in WebP

file header documentation?
https://code.google.com/p/webp/issues/detail?id=241

I made an update to the document which has been merged. Thanks for the
report!
I'll close this once the copy on developers.google.com has been updated.

https://gerrit.chromium.org/gerrit/#/c/73776/
b510fbf doc/webp-container-spec: note MSB order for chunk diagrams

[we...@googlecode.com]

Updates:
Status: Verified

Comment #3 on issue 241 by pascal.m...@gmail.com: Incorrect flag details in

WebP file header documentation?
https://code.google.com/p/webp/issues/detail?id=241

doc page[1] has been refreshed. Thanks for the report!

[1] https://developers.google.com/speed/webp/docs/riff_container

[we...@googlecode.com]

Comment #4 on issue 241 by drewnoakes: Incorrect flag details in WebP file
header documentation?
https://code.google.com/p/webp/issues/detail?id=241

Thanks for the clarification. MSb order does make more sense in the layout
diagram. My brain reassociated the given indices with the (more familiar to
me) LSb ordering.