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

[Michael Niedermayer]

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 ?

thx

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

No great genius has ever existed without some touch of madness. -- Aristotle
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