Yes, PixaFlux includes a Lattice node that allows you to deform any picture with a free form deformation lattice. PixaFlux is still on development, so I will send you later a short tutorial showing you how to do this.
PixaFlux is a free texture authoring tool like Substance Painter, but free. Obviously it isn't as easy to use, and I don't know how powerful it is in comparison, but it's worth a look.
Best bet is procedural algorithmic tools.
This has potential that I stumbled upon:
http://www.pixaflux.com/index.php
You probably have some similar Blender plugin somewhere.
There are probably others but I'm not that familiar with them.
You can do that on PixaFlux if you are open to other software.
PixaFlux is a parametric image compositor that uses a node graph to do all image operation. In this case you need 3 Reader nodes with your Red, Green and Blue layers, and one Mix node set to average. Connect the 3 Reader nodes to the inputs of the Mix node. This will create a new image where each layer contributes the same amount to the output (33.33%).
If you want to increase the contribution of one layer, say Red 50%, Green 25% and Blue 25%, then you can connect the Red channel 2 times.
This short video will show you what is PixaFlux and how it works.
Can I suggest you to use my software: PixaFlux.
It is a non-destructive image editing application that uses a node graph instead of layers. You can use nodes to add images to your project and compose them in many different ways, and at the end you can have one or more resize nodes that change the size to whatever you need.
The software is mature, and I am really interested in finding beta testers. If you are interested and decide to work with PixaFlux I can create some examples and tutorials about how you can use it in your workflow. I can also develop new nodes and tools if you need them!
Thanks!