About: Max quality not higher than current quality (default).
I would like to thank you for this comments posibility, positively.
Next, I would like to note to your experts users if a jpeg should be probed for its quality setting (like the figure Irfanview provides; not sure if it's a meta data and/or calculated), and default a higher destination quality setting would be lowered consequently, much like the 'only shrink pictures' option. Although enlarging images can be useful.
Perhaps creating a 90% quality out of a 70% quality image increases the file size or not; it does give a new quality as if it's a 90% quality image. If I'm not mistaken.
On another note:
Not sure if a simple arithmetic (peace of code) could advise if the picture should be a vector image in the first place. Or a Mondrian png/gif.
Thank you. I'm using Ubuntu Linux by the way, but I do recommend your programme to Windows users I know.