Is there any java Gimp library to control, resize, or reduce image size (MB to KB) ? I'm looking for something like JGIMP.
I tried to work on JGIMP , but it was an older version, and failed to install in fedora 23.
I don't know of a working Java Gimp Library but there is a couple of Java interfaces to ImageMagick that will let you do everything in your examples.
ImageMagick runs on Linux, Windows, Mac Os X, iOS, Android OS, etc., and by itself provides a command line interface to do just about any image manipulation that you can think of.
You might also like to take a look at Marvin which claims: "Pure Java cross-platform image processing framework that provides features for image and video frame processing, multi-threading image processing, GUI integration, extensibility via plug-ins, unit text automation among other things."
Complementing the answer given by Steve, Marvin Framework perfectly suits for your case since it's a framework that you can use to develop your own image processing applications and because it has its own image editor. So you can test the algorithms without developing a software.
Current Marvin Algorithms:
If you want to resize images, take a look at the following question:
How do you create a thumbnail image out of a JPEG in Java?
Marvin Questions on Stack Overflow (Good source of examples):