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

[GStreamer (GNOME Bugzilla)]

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

--- Comment #17 from Aaron Boxer <boxerab at gmail.com> ---
(In reply to Sebastian Dröge (slomo) from comment #16)
> Sure, that's fine, it just seems like I'm misunderstanding something with
> the patch :)

no problem :)


> 
> (In reply to Aaron Boxer from comment #14)
> > (In reply to Sebastian Dröge (slomo) from comment #13)
> > > Review of attachment 353729 [details] [review] [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?

I am just trying to re-use the R value in the G and B channels. R == tmp[1]
Just save a little calculation :)

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