[FFmpeg-devel] [RFC PATCH v5 2/3] libavcodec/j2kenc: Fix tag tree coding

[Michael Niedermayer]

On Wed, Aug 26, 2020 at 08:38:30AM +0530, Gautam Ramakrishnan wrote:
> On Wed, Aug 26, 2020 at 4:04 AM Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> >
> > On Tue, Aug 25, 2020 at 07:25:44PM +0530, gautamramk at gmail.com wrote:
> > > From: Gautam Ramakrishnan <gautamramk at gmail.com>
> > >
> > > The implementation of tag tree encoding was incorrect.
> > > However, this error was not visible as the current j2k
> > > encoder encodes only 1 layer.
> > > This patch fixes tag tree coding for JPEG2000 such tag
> > > tree coding would work for multi layer encoding.
> >
> > [...]
> >
> > > diff --git a/libavcodec/jpeg2000.c b/libavcodec/jpeg2000.c
> > > index 26e09fbe38..2e26bc5b00 100644
> > > --- a/libavcodec/jpeg2000.c
> > > +++ b/libavcodec/jpeg2000.c
> > > @@ -82,12 +82,13 @@ static Jpeg2000TgtNode *ff_jpeg2000_tag_tree_init(int w, int h)
> > >      return res;
> > >  }
> > >
> > > -void ff_tag_tree_zero(Jpeg2000TgtNode *t, int w, int h)
> > > +void ff_tag_tree_zero(Jpeg2000TgtNode *t, int w, int h, int val)
> > >  {
> > >      int i, siz = ff_tag_tree_size(w, h);
> > >
> > >      for (i = 0; i < siz; i++) {
> > > -        t[i].val = 0;
> > > +        t[i].val = val;
> > > +        t[i].temp_val = 0;
> > >          t[i].vis = 0;
> > >      }
> > >  }
> > > @@ -567,8 +568,8 @@ void ff_jpeg2000_reinit(Jpeg2000Component *comp, Jpeg2000CodingStyle *codsty)
> > >              Jpeg2000Band *band = rlevel->band + bandno;
> > >              for(precno = 0; precno < rlevel->num_precincts_x * rlevel->num_precincts_y; precno++) {
> > >                  Jpeg2000Prec *prec = band->prec + precno;
> > > -                ff_tag_tree_zero(prec->zerobits, prec->nb_codeblocks_width, prec->nb_codeblocks_height);
> > > -                ff_tag_tree_zero(prec->cblkincl, prec->nb_codeblocks_width, prec->nb_codeblocks_height);
> > > +                ff_tag_tree_zero(prec->zerobits, prec->nb_codeblocks_width, prec->nb_codeblocks_height, 0);
> > > +                ff_tag_tree_zero(prec->cblkincl, prec->nb_codeblocks_width, prec->nb_codeblocks_height, 0);
> >
> > this looks a bit like a somewhat unlrelated bugfix thats spread over this and
> > the next patch
> > if so, that should be moved into a seperate patch
> > the patches are already complex without an additional bugfix in them
> >
> This portion is a fix for what you pointed out yesterday saying that
> the parent of a the
> nodes are not getting set. I thought this would be an appropriate
> patch to fix this. Do you
> feel its better that this part is made separate though?

> In my opinion, only this patch provides the bug fix and the next patch
> just uses the fix.
> Do correct me if I am wrong.

IIUC the problem is that the tag trees are inefficient, so a bugfix would
change the output files and make them bit smaller.
the 1/3 & 2/3 patches do not change the output of any fate tests so they
do not seem to fix this on their own. The 3/3 patch adds multi layer stuff
so the bugfix seemed intermingled with that, which is what i thought was
not optimal. Its not the end of the world if these are mixed but it should
be for a very good reason then. For example if seperating the fix would be
a unreasonable amount of work and make the changes alot more complex ...
But in 99% of the cases bugfixes really should be seperate it makes
understanding chnages, testing changes and also things like future regression
testing easier.

Thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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