I'm trying to use the command convert -resize 1024X768 source.png dest.jpg on a sequence of images. I need it to be applied to all the images which I can do by convert -resize 1024X768 *.png but I'd like to know how to supply the same filename as the destination.

I'm only using the convert command as an example.

You can try with a for command line

Test with a 'dry run',

for i in *.png;do echo convert -resize 1024X768 "$i" "$i/.png.jpg";done

and when its output looks good, remove echo and do the conversion,

for i in *.png;do convert -resize 1024X768 "$i" "$i/.png.jpg";done

Alternative with find and rename

If you want to avoid a loop in bash, you can use find,

find -maxdepth 1 -name "*.png" -exec echo convert -resize 1024X768 .jpg ;

and when its output looks good, remove echo and do the conversion,

find -maxdepth 1 -name "*.png" -exec convert -resize 1024X768 .jpg ;

After that you can use rename to make the target file names nicer (prune the clumsy double extension)

rename -n s/.png.jpg$/.jpg/ *.png.jpg

and when its output looks good, remove -n and do the real renaming,

rename s/.png.jpg$/.jpg/ *.png.jpg

There are probably ways to do this in one step (without renaming), but I don't know how. Maybe someone will chip in and describe a way to do it.