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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

Change-Id: I56a575529862dfc8ad189ddcfc47ef59a58f273d
This commit is contained in:
Pascal Massimino 2014-09-18 08:21:02 +02:00
parent b901416b90
commit d7167ff7ce
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_
Paragraphs marked as \[AMENDED\] were amended on 2014-09-16.
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);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The version_number is a 3 bit code that must be discarded by the decoder
at this time. Complying encoders write a 3-bit value 0.
The version_number is a 3 bit code that must be set to 0. Any other value
should be treated as an error. \[AMENDED\]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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));
// Return either left or top, the one closer to the prediction.
if (pL <= pT) {
if (pL < pT) { // \[AMENDED\]
return L;
} else {
return T;
@ -542,6 +543,9 @@ color.
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
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