[Bug 783591] openjpegdec: doesn't support grayscale with alpha

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=783591

--- Comment #16 from Sebastian Dröge (slomo) <slomo at coaxion.net> ---
Sure, that's fine, it just seems like I'm misunderstanding something with the
patch :)

(In reply to Aaron Boxer from comment #14)
> (In reply to Sebastian Dröge (slomo) from comment #13)
> > Review of attachment 353729 [details] [review] [review]:
> Thanks for the review
> 
> > 
> > ::: ext/openjpeg/gstopenjpegdec.c
> > @@ +425,3 @@
> > +      tmp[1] = off[0] + (*data_in[0] << shift[0]);
> > +      tmp[2] = tmp[1];
> > +      tmp[3] = tmp[1];
> > 
> > Why are you generating something like RAGB here, i.e. alpha on the second
> > component and all other components the same value?
> 
> I assume that alpha is always in the last component : component == 1. Since
> format is ARGB, and tmp[0] stores alpha in output, we need tmp[0] =  off[1]
> + (*data_in[1] << shift[1]);

But shouldn't that then be
tmp[0] = off[1] ...
tmp[1] = off[0] ...
tmp[2] = off[0] ...
tmp[3] = off[0] ...

I.e. alpha goes to alpha, grey value goes to R,G,B?

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