Table of Contents
Photoshop
You will have to buy/download it on your own.
Necessary Plug-Ins:
NVIDIA TEXTURE TOOLS (only works with Nvidia graphic cards)


Standard export settings:


INTEL TEXTURE WORKS (works with all graphic cards)

Standard export settings:

Gimp
Free image editor, similiar to Photoshop.
No Plug-Ins needed.
XNConvert
Batch image processor, can convert from and to .dds. No need to purchase, free is enough.
Waifu2x
Upscaling with detail preservation, helps to improve texture quality and reduce noise
Waifu 2x caffee

Download, higher denoise and better scaling
https://github.com/lltcggie/waifu2x-caffe/releases

waifu 2x extension GUI

Download, most complicated, most customization options
https://github.com/AaronFeng753/Waifu2x-Extension-GUI/releases

League of Legends tools
Tex2dds – convert .tex files
Convert .tex files to editable .dds files and you can convert .dds back to .tex after editing.
Might not work with giant image dimensions.
Miscellaneous Tools
PHOTOPEA
Free online-editor for Photoshop .psd files