[FFmpeg-devel] [PATCH 2/5] libavcodec/jpeg2000dec.c: Modify image dimensions

[Carl Eugen Hoyos]

Am Mo., 22. Juni 2020 um 23:32 Uhr schrieb Michael Niedermayer
<michael at niedermayer.cc>:
>
> On Mon, Jun 22, 2020 at 12:12:05AM +0530, gautamramk at gmail.com wrote:
> > From: Gautam Ramakrishnan <gautamramk at gmail.com>
> >
> > Reduce image size of the image if all components have
> > a non zero sample separation. This is to replicate the
> > output of opj_decompress.
> > ---
> >  libavcodec/jpeg2000dec.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> >
> > diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
> > index ab36009a2d..05e85f4317 100644
> > --- a/libavcodec/jpeg2000dec.c
> > +++ b/libavcodec/jpeg2000dec.c
> > @@ -269,6 +269,8 @@ static int get_siz(Jpeg2000DecoderContext *s)
> >      const enum AVPixelFormat *possible_fmts = NULL;
> >      int possible_fmts_nb = 0;
> >      int ret;
> > +    int o_dimx, o_dimy; //original image dimensions.
> > +    int dimx, dimy;
> >
> >      if (bytestream2_get_bytes_left(&s->g) < 36) {
> >          av_log(s->avctx, AV_LOG_ERROR, "Insufficient space for SIZ\n");
> > @@ -371,11 +373,18 @@ static int get_siz(Jpeg2000DecoderContext *s)
> >      }
> >
> >      /* compute image size with reduction factor */
> > -    ret = ff_set_dimensions(s->avctx,
> > -            ff_jpeg2000_ceildivpow2(s->width  - s->image_offset_x,
> > -                                               s->reduction_factor),
> > -            ff_jpeg2000_ceildivpow2(s->height - s->image_offset_y,
> > -                                               s->reduction_factor));
> > +    o_dimx = ff_jpeg2000_ceildivpow2(s->width  - s->image_offset_x,
> > +                                               s->reduction_factor);
> > +    o_dimy = ff_jpeg2000_ceildivpow2(s->height - s->image_offset_y,
> > +                                               s->reduction_factor);
> > +    dimx = ff_jpeg2000_ceildiv(o_dimx, s->cdx[0]);
> > +    dimy = ff_jpeg2000_ceildiv(o_dimy, s->cdy[0]);
> > +    for (i = 1; i < s->ncomponents; i++) {
> > +        dimx = FFMAX(dimx, ff_jpeg2000_ceildiv(o_dimx, s->cdx[i]));
> > +        dimy = FFMAX(dimy, ff_jpeg2000_ceildiv(o_dimy, s->cdy[i]));
> > +    }
> > +
> > +    ret = ff_set_dimensions(s->avctx, dimx, dimy);
> >      if (ret < 0)
> >          return ret;
>
> I think the resolution, the pixel format and any odd-format-handling
> code probably need to be adjusted together.
> Changing just the dimension code to select a higher resolution when
> chroma or alpha planes are of higher resolution then luma. Will
> probably not work if there is neither a pixel format selected that
> represents that nor code to compensate for this (as mjpeg does)
> but i might be missing something
>
> is there some testcase this fixes or improves ?

At least p1_01.j2k which has one component.

Carl Eugen