[FFmpeg-devel] [PATCH 2/2] pixdesc: deprecate AV_PIX_FMT_FLAG_PSEUDOPAL

Vittorio Giovara vittorio.giovara at gmail.com
Tue Apr 3 13:07:43 EEST 2018

On Thu, Mar 29, 2018 at 03:30:43PM +0200, wm4 wrote:
>* PSEUDOPAL pixel formats are not paletted, but carried a palette with the
*>* intention of allowing code to treat unpaletted formats as paletted. The
*>* palette simply mapped the byte values to the resulting RGB values,
*>* making it some sort of LUT for RGB conversion.
*> >* It was used for 1 byte formats only: RGB4_BYTE, BGR4_BYTE, RGB8, BGR8,
*>* GRAY8. The first 4 are awfully obscure, used only by some ancient bitmap
*>* formats. The last one, GRAY8, is more common, but its treatment is
*>* grossly incorrect. It considers full range GRAY8 only, so GRAY8 coming
*>* from typical Y video planes was not mapped to the correct RGB values.
*>* Also, nothing actually used the PSEUDOPAL palette data, except xwdenc.
*>* All other code had to treat it as a special case, just to ignore or
*>* propagate palette data.
*> >* In conclusion, this was just a very strange old hack that has no real
*>* justification to exist. It's negatively useful, because API users who
*>* allocate their own pixel data have to be aware that they need to
*>* allocate the palette, or FFmpeg will crash on them in _some_ situations.
*>* On top of this, there was no API to allocate the pseuo palette outside
*>* of av_frame_get_buffer(). (avpriv_set_systematic_pal2() was not public,
*>* which is good, because GRAY8 treatment is broken.)
*> >* This patch not only deprecates AV_PIX_FMT_FLAG_PSEUDOPAL, but also makes
*>* the pseudo palette optional. Nothing accesses it anymore, though if it's
*>* set, it's propagated. It's still allocated and initialized for
*>* compatibility with API users that rely on this feature. But new API
*>* users do not need to allocate it. This was an explicit goal of this
*>* patch.
*> >* Most changes replace AV_PIX_FMT_FLAG_PSEUDOPAL with FF_PSEUDOPAL. I
*>* first tried #ifdefing all code, but it was a mess. The FF_PSEUDOPAL
*>* macro reduces the mess, and still allows defining FF_API_PSEUDOPAL to 0.
*> >* Passes FATE with FF_API_PSEUDOPAL enabled and disabled. In addition,
*>* FATE passes with FF_API_PSEUDOPAL set to 1, but with allocation
*>* functions manually changed to not allocating a palette.
*>* ---*

set looks good to me

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