When saving images in this format, you will be able to specify a quality factor that can range from 0 to 100. The higher the number, the larger the file produced and the better the quality of the image.
Not sure if a script like this exists.
It may be useful in some cases.
Fits all layers (or 'only visible' layers) to image size.
Install script in your scripts directory
(you can see the scripts directory by going to
Edit -> Preferences
and then once the preferences windows opens,
go to Folders -> Scripts)
How to test:
* Create a new image (say: 800x600px)
* Create another, but smaller image (say 100x100px)
* Copy the small image (Ctrl+C)
* Paste in the bigger image (and create a new layer)
* Duplicate this new layer a couple of times
These two scripts help you with some basic operations on images with a lot of layers (some hundreds or so), for instance when you work on animations (one frame consists of several layers, which belong together). You can set linking and visibility status, opacitymode, and (or) process opacity fadings, which all can be done repeatedly for subgroups or for independant single layers (by stepping throughout the whole layerstack or by a definable cyclelength).