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pixdesc: clarify AV_PIX_FMT_FLAG_ALPHA doxygen 

Also make clear that PAL8 can have alpha.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
wm4 2015-02-10 12:18:13 +01:00 committed by Michael Niedermayer
parent 92e3a6fdac
commit c247fc63e4
2 changed files with 14 additions and 3 deletions
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13
libavutil/pixdesc.h
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@ -139,8 +139,19 @@ typedef struct AVPixFmtDescriptor {
* An example of a pseudo-paletted format is AV_PIX_FMT_GRAY8
*/
#define AV_PIX_FMT_FLAG_PSEUDOPAL (1 << 6)
/**
* The pixel format has an alpha channel.
* The pixel format has an alpha channel. This is set on all formats that
* support alpha in some way. The exception is AV_PIX_FMT_PAL8, which can
* carry alpha as part of the palette. Details are explained in the
* AVPixelFormat enum, and are also encoded in the corresponding
* AVPixFmtDescriptor.
*
* The alpha is always straight, never pre-multiplied.
*
* If a codec or a filter does not support alpha, it should set all alpha to
* opaque, or use the equivalent pixel formats without alpha component, e.g.
* AV_PIX_FMT_RGB0 (or AV_PIX_FMT_RGB24 etc.) instead of AV_PIX_FMT_RGBA.
*/
#define AV_PIX_FMT_FLAG_ALPHA (1 << 7)

4
libavutil/pixfmt.h
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@ -44,11 +44,11 @@
* big-endian CPUs.
*
* @par
* When the pixel format is palettized RGB (AV_PIX_FMT_PAL8), the palettized
* When the pixel format is palettized RGB32 (AV_PIX_FMT_PAL8), the palettized
* image data is stored in AVFrame.data[0]. The palette is transported in
* AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is
* formatted the same as in AV_PIX_FMT_RGB32 described above (i.e., it is
* also endian-specific). Note also that the individual RGB palette
* also endian-specific). Note also that the individual RGB32 palette
* components stored in AVFrame.data[1] should be in the range 0..255.
* This is important as many custom PAL8 video codecs that were designed
* to run on the IBM VGA graphics adapter use 6-bit palette components.