[FFmpeg-devel] [PATCH] avfilter: add unpremultiply filter

[Tobias Rapp]

On 01.08.2017 15:31, Paul B Mahol wrote:
> On 8/1/17, Tobias Rapp <t.rapp at noa-archive.com> wrote:
>> On 01.08.2017 13:03, Paul B Mahol wrote:
>>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>>> ---
>>>  doc/filters.texi             |  13 ++
>>>  libavfilter/Makefile         |   1 +
>>>  libavfilter/allfilters.c     |   1 +
>>>  libavfilter/vf_premultiply.c | 307
>>> ++++++++++++++++++++++++++++++++++++-------
>>>  4 files changed, 277 insertions(+), 45 deletions(-)
>>>
>>> diff --git a/doc/filters.texi b/doc/filters.texi
>>> index 4089135..a50696a 100644
>>> --- a/doc/filters.texi
>>> +++ b/doc/filters.texi
>>> @@ -14532,6 +14532,19 @@ ffmpeg -i INPUT -vf trim=duration=1
>>>
>>>  @end itemize
>>>
>>> + at section unpremultiply
>>> +Apply alpha unpremultiply effect to input video stream using first plane
>>> +of second stream as alpha.
>>> +
>>> +Both streams must have same dimensions and same pixel format.
>>> +
>>> +The filter accepts the following option:
>>> +
>>> + at table @option
>>> + at item planes
>>> +Set which planes will be processed, unprocessed planes will be copied.
>>> +By default value 0xf, all planes will be processed.
>>> + at end table
>>
>> IMHO using a flags-like string "planes=rgb" would be more user-friendly
>> than a bitmask. At least the documentation should tell which bit refers
>> to what channel.
>
> It is directly related to pixel format.

I'm just wondering whether I can apply the logic of 
AVPixFmtDescriptor.comp to the planes bitmask or not:

     /**
      * Parameters that describe how pixels are packed.
      * If the format has 1 or 2 components, then luma is 0.
      * If the format has 3 or 4 components:
      *   if the RGB flag is set then 0 is red, 1 is green and 2 is blue;
      *   otherwise 0 is luma, 1 is chroma-U and 2 is chroma-V.
      *
      * If present, the Alpha channel is always the last component.
      */

Regards,
Tobias