I love the Gingham effect on Instagram! Sometimes I want to apply it to some pictures to use on other platforms so I end up loading photos on my phone just to apply the effect, download them back on my computer and them use them wherever I want but, come on, that's not practical at all!
So, to make things easier, I've been experimenting with Color Levels on GIMP to achieve the same effect and I think I'm pretty close to it. At least, I can say that I'm satisfied with it.
This is a sample image:
This one was altered using Instagram:
And this one was altered using this setup:
Again, it is not 100% perfect but it looks pretty close!
If you want, just download it and import on your GIMP.
Feel free to fork it and improve it.
Thanks!
João R.G. Sampaio