[FFmpeg-devel] Optimised math functions in FFMPEG?

[Paul Buxton]

Thanks both.

I have implemented the algorithm in this paper
https://www.researchgate.net/publication/275213614_A_New_Color_Correction_Method_for_Underwater_Imaging

Which basically converts to an L A B (not CIELAB) colorspace, subtracts the
average value of the frame from each pixel and converts back.

Yes I did put the linearisation /de-linearisation into the filter. Not
applying it produces noticeably incorrect results. Is there instead a way
to tell the filtergraph that the filter expects and outputs linear data?

I can investigate an integer version.


On Sun, Aug 15, 2021 at 2:31 PM Paul B Mahol <onemda at gmail.com> wrote:

> On Sun, Aug 15, 2021 at 3:27 PM Nicolas George <george at nsup.org> wrote:
>
> > Paul Buxton (12021-08-15):
> > > I have my filter working nicely but it is a little slow. I have
> > > parallelised it where possible, but it is still a bit heavy. I am
> > wondering
> > > if there are any optimised implementations/approximations of some math
> > > functions built in that I should use instead of the standard library
> > > implementations.
> > > Specifically any of
> > > pow()
> > > exp()
> > > log()
> > >
> > > I have done a quick grep of the code but can't see any likely
> contenders.
> >
> > I am not aware we have those. The kind of optimization you can do
> > depends a lot on your use case. Please give a little details.
> >
> > If you want to speed your filter up, the best would be to make it work
> > with integers. It would also allow to make reliable unit tests.
> >
>
>
> If you convert to/from linear light inside filter, that is wrong thing to
> do.
>
>
> >
> > Regards,
> >
> > --
> >   Nicolas George
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