Here is the full guide on how to install GIMP Portable on Ubuntu. Follow the steps to install it and run it.  This works for me in Kubuntu 16.04 64bit. It should also work in other 16.x 64bit ‘buntus.  It might even work in equivalent version of Mint. A long shot possibility in other Debian based versions.

Nothing clever, it is assembled using a script and the ‘buntu ‘gimp-edge’ ppa. This updates regularly and I will attempt to keep the following to the current build.
More dependency hell with Ubuntu 18.x versions. This Gimp 2.9.9 appimage is stuck with this release which is Dec 2017
Still very usable, no recent feature additions, just bug fixes

Download GIMP Portable for Ubantu

Download GIMP Portable 2.9.9 for ubantu

How to install GIMP Portable on Ubantu

Unzip and run. It will run from your home partition. Same as a regular gimp, first run it creates a gimp profile, in this case ~/.config/GIMP/2.9  It will copy all your resources from ~/.gimp-2.8 so to save a lot of editing, temporarily rename ~/.gimp-2.8 and a new empty Gimp 2.9 profile is created.

Here is the images for GIMP portable on ubantu

I am not keen on those dark themes, so this is my preference + a shot of one nice addition to Gimp 2.9 – new layer options.  Plenty other new things to explore in GIMP portable on Ubuntu.

bimp17x64 <<< this has a dependency libpcre3 – install that package from your linux repository.
fourierx64
djvu-read <<< mainly for those academic documents

gmic_gimp_qt
gmic_gimp179 <<< last of the series, can be installed alongside ver 2.0 installed.

guillotine-into-layersx64
nufraw-gimp
plasma2x64
plugin-heal-selection.py
resynthesizer29
resynthesizer_gui29 <<< small change to gui with added options
smooth-path64

Bugs

This is a development version, there will be bugs.
If Gimp 2.9.9 – any version – crashes a lot, first thing to check is
Edit -> Preferences -> System Resources -> Number-of-Threads-to-use Set this to 1

Also do checkout plugins for GIMP Portable

Photoshop filter plugin (PSPI) for GIMP

The user interface of GIMP is designed by a dedicated design and usability team. This team was formed after the developers of GIMP signed up to join the OpenUsability project. A user interface brainstorming group has since been created for GIMP, where users of GIMP can send in their suggestions as to how they think the GIMP user interface could be improved.

GIMP is presented in two forms, single and multiple window mode; GIMP 2.8 defaults to the multiple-window mode. In multiple-window mode a set of windows contains all GIMP’s functionality. By default, tools and tool settings are on the left and other dialogues are on the right. A layers tab is often to the right of the tools tab, and allows a user to work individually on separate image layers. Layers can be edited by right-clicking on a particular layer to bring up edit options for that layer. The tools tab and layers tab are the most common dockable tabs.

ref – https://www.gimp-forum.net/Thread-Portable-Gimp-2-9-9-for-linux