Are images automatically optimized in GK Image Show 4?

Using the slideshow component (GK Image Show 4 v1.36) I would like to know if the images I provide will be automatically optimized.

For example:
If I add an image which are 8000 x 4000 pixels ... which is too big ... will the component automatically fix and optimize this to a lower resolution?

Yes, you only need to enable option Generate Thumbnails in Image Show configuration http://d.pr/i/sFEy

Ok, but if I don't use any thumbnails (I just show a big wide image streched all over the screen)? Are the big image also optimized?

When you use responsive style (and the Creativity is one of them) the image will be display in 100% wide and the height is set to auto so you should see whole image.