col,row coordinates from utmx,utmy coordinates

Hi!
Given a jpg + jpgw files I would like
to get the col,row coordinates of the jpg file
that correspond to a set of projected
utmx, utmy coordinates, best
not having to import the jpg file into R because of its size.
Does this exist within R (in raster package or any other)?
Or should I use spgrass and/or rsaga?

Thanks

Agus


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