This is unimpressive. Dragging more than one file to the icon will result in a batch window that has two major problems:
Only allows export to JPG
Cannot compress by quality, only estimated file size. If you guess too little, you will be looking at a garbled mess.
Actually you are wrong. You can use the same settings in batch also.
You can close the batch window, choose your settings, including output format, metadata, image adjustments, etc then open Batch window again, verify settings there also and press Start.
By default it uses JPEG and your last saved settings, but yon can choose PNG also.
I am working on the RIOT documentation also which will clarify other things for first time users.
The basic RIOT batch-mode work-flow is different than in other batch programs
- open one picture from the list
- choose the most suitable settings
- open batch window and add all files
- verify batch settings then press Start
I noticed in your screenshot you have not checked "best compression" in the PNG settings. Note that for performance reasons a fast PNG compression is applied by default which is a poor compression. For final results always check "best compression". The reason RIOT uses a fast compression by default is to be able to make all your adjustments without waiting for that slow high compression until you are happy with the results.
Also I recommend to use pngout or the faster advpng with RIOT. Currently these methods *usually* give better compression than the internal "best compression".
An automatic optimization mode like you mentioned is planned.