[FFmpeg-devel] [PATCH] lavfi: add xbr filter

[arwa arif]

On Mon, Oct 27, 2014 at 2:35 PM, Clément Bœsch <u at pkh.me> wrote:

> On Mon, Oct 27, 2014 at 10:02:25AM +0100, Nicolas George wrote:
> > Le sextidi 6 brumaire, an CCXXIII, arwa arif a écrit :
> > > I have done all the changes except rgb to yuv conversion. I will most
> > > probably do it by tonight.
> >
> > > +    /*Convert RGB to Y'UV*/
> > > +    int y = r * .299000 + g * .587000 + b * .114000;
> > > +    int u = r * -.168736 + g * -.331264 + b * .500000;
> > > +    int v = r * .500000 + g * -.418688 + b * -.081312;
> > > +
> > > +    /*Add HQx filters threshold & return*/
> > > +    return (y*48) + (u*7) + (v*6);
> >
> > A bit of maths would greatly help simplifying the code here. I am too
> lazy
> > to make the computations myself, so according to PARI/GP, just
> copy-pasting
> > your formulas (and trimming useless zeros from the output to make it more
> > readable):
> >
> > ? y = r * .299000 + g * .587000 + b * .114000;
> > ? u = r * -.168736 + g * -.331264 + b * .500000;
> > ? v = r * .500000 + g * -.418688 + b * -.081312;
> > ? (y*48) + (u*7) + (v*6)
> > %4 = 16.170848*r + (23.345024*g + 8.484128*b)
> >
> > Since your numbers are all integers in the [-255;+255] range and your
> > computations are made on 32-bits integers, scaling everything by a
> factor K
> > would work for K between roughly 256 and 170000. Using 65536 seems like a
> > good choice:
> >
> > return (1059773 * r + 1529939 * g + 556016 * b) >> 16;
> >
> > Of course, in this kind of case, a comment must be added to explain where
> > the numbers come from.
> >
>
> The specs says it's the same algorithm as HQx, the code just needs to be
> refactored, the integer convertion is already written there.
>
> [...]
>
> --
> Clément B.
>


Updated the patch.


>
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