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Amend the lossless spec according to issue #205, #206 and #224

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http://code.google.com/p/webp/issues/detail?id=205 <- Select()
http://code.google.com/p/webp/issues/detail?id=206 <- out-of-bound colormap index
http://code.google.com/p/webp/issues/detail?id=224 <- version number MUST be 0

(cherry picked from commit d7167ff7ce)

Change-Id: I56a575529862dfc8ad189ddcfc47ef59a58f273d
This commit is contained in:
Pascal Massimino 2014-09-18 08:21:02 +02:00 committed by James Zern
parent 9102a7b63d
commit f8b7d94daa
1 changed files with 7 additions and 3 deletions
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10
doc/webp-lossless-bitstream-spec.txt
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@ -14,6 +14,7 @@ Specification for WebP Lossless Bitstream
_Jyrki Alakuijala, Ph.D., Google, Inc., 2012-06-19_ _Jyrki Alakuijala, Ph.D., Google, Inc., 2012-06-19_
Paragraphs marked as \[AMENDED\] were amended on 2014-09-16.
Abstract Abstract
-------- --------
@ -172,8 +173,8 @@ It should be set to 0 when all alpha values are 255 in the picture, and
int alpha_is_used = ReadBits(1); int alpha_is_used = ReadBits(1);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The version_number is a 3 bit code that must be discarded by the decoder The version_number is a 3 bit code that must be set to 0. Any other value
at this time. Complying encoders write a 3-bit value 0. should be treated as an error. \[AMENDED\]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int version_number = ReadBits(3); int version_number = ReadBits(3);
@ -330,7 +331,7 @@ uint32 Select(uint32 L, uint32 T, uint32 TL) {
abs(pGreen - GREEN(T)) + abs(pBlue - BLUE(T)); abs(pGreen - GREEN(T)) + abs(pBlue - BLUE(T));
// Return either left or top, the one closer to the prediction. // Return either left or top, the one closer to the prediction.
if (pL <= pT) { if (pL < pT) { // \[AMENDED\]
return L; return L;
} else { } else {
return T; return T;
@ -542,6 +543,9 @@ color.
argb = color_table[GREEN(argb)]; argb = color_table[GREEN(argb)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the index is equal or larger than color_table_size, the argb color value
should be set to 0x00000000 (transparent black). \[AMENDED\]
When the color table is small (equal to or less than 16 colors), several When the color table is small (equal to or less than 16 colors), several
pixels are bundled into a single pixel. The pixel bundling packs several pixels are bundled into a single pixel. The pixel bundling packs several
(2, 4, or 8) pixels into a single pixel, reducing the image width (2, 4, or 8) pixels into a single pixel, reducing the image width