[gdal-dev] What happens by default when writing RGBA into jpeg?

[Even Rouault]

> Thanks, that makes sense. However, the result is somehow surprising and I
> guess that in most cases unusable for the user. I wonder if it would be good
> to print something like "WARNING. Encountered 4 source bands, assuming CMYC
> color space". Behaviour is not very easy to understand by reading the driver
> page http://www.gdal.org/frmt_jpeg.html
>
> When I try to look at the situation as a QGIS user sees it, it feels like
> there is a bug somewhere but I can't say exactly where. However, I do not
> believe that any average QGIS user can have success with converting their
> RGBA tiffs into jpeg format even it is possible by editing gdal_translate
> command manually.

Agreed that the current behaviour is confusing. A check could be done on the
color interpretation of the source bands to check if it is C,M,Y,K when a 4 band
dataset is provided. If not, then output the warning (and possibly error out if
-strict is specified)