[FFmpeg-devel] [PATCH V2] lavfi/vf_nlmeans: Improve the performance for nlmeans

[mypopy at gmail.com]

On Fri, Feb 1, 2019 at 5:11 PM Clément Bœsch <u at pkh.me> wrote:
>
> On Fri, Feb 01, 2019 at 04:57:37PM +0800, mypopy at gmail.com wrote:
> [...]
> > > > -#define WEIGHT_LUT_NBITS 9
> > > > -#define WEIGHT_LUT_SIZE  (1<<WEIGHT_LUT_NBITS)
> > > > +#define WEIGHT_LUT_SIZE  (800000) // need to >  300 * 300 *
log(255)
> > >
> > > So the LUT is now 3.2MB?
> > >
> > > Why 300? 300*300*log(255) is closer to 500 000 than 800 000
> > I just seleted a value > 300*300*log(255) (500 000 more precise) for
> > this case at liberty in fact , the other option is use a dynamic
> > allocation memory for weight_lut table size base on the
> > max_meaningful_diff :), but maybe seems pretty obvious, I think 3M is
> > not a big burden for nlmeans
>
> It's probably fine yes, I'm just confused at the comment: why does it
> *needs* to be > 300 * 300 * log(255)?
>
> --
ohhh, 300 = max(s) * 10 :), max(s) = 30, this is the reason.

In fact, max size of WEIGHT_LUT_SIZE ==  max (max_meaningful_diff), then we
can avoid use pdiff_lut_scale in nlmeans, becasue now pdiff_lut_scale == 1.
:)

and max( max_meaningful_diff ) = -log(-1/255.0) * h * h = log(255) * max
(h) * max(h) = log(255) * max (10*s) * max(10*s)