Hi
Would be nice with an option to change the JPEG quality without rescaling an image. Seems like this is not possible with the current options. I often want to only reduce the compression quality.
Well, there is, already. You can use something like
Image CONVERT=jpg NOREDUCE PERCENT=75to keep your size, but reduce the quality. Just change the value to what you actually need.
Alternatively you can untick the scaling option in the convert dialog.
You may need to add the NOLOSSLESS argument to the command, if all you want to do is recompress the JPEG without making any other changes.
(Normally, Opus attempts to modify JPEGs without recompressing them, if possible; an image conversion which doesn't do anything would normally not touch the file at all, but the NOLOSSLESS argument overrides that.)
Oops, sorry, the NOREDUCE parameter seemed to do that already in a quick test.
"Image CONVERT=jpg NOREDUCE PERCENT=75" Does not work. Cant see any different in filesize. What am i doing wrong?
Abr's example was quite wrong. 
Try this (assuming you want 75% quality, and also that you want to replace the image where it is without keeping a backup copy):
Image CONVERT=jpg QUALITY=75 HERE NOLOSSLESSPlease link your account if you need more detailed help.