Where did you learn how to do this?

I am also curious to know how they can make so very complex and complicated mix of nodes and components to make that the filters gives the desired result.

Many know much about programming and how to make scripts and program them, and also now very well how to combine components and what effects will have them when mixing all toghether.

and best of all is if they have an idea and a project to make, they know what filter forges tools, nodes and components to use in the right way and combine them to be able to get the filter final result.

I really admire and respect much all the genius and very skilled and talented people that are here making such wonderful, interesting and useful filters.

Thanks very much for all the knowledge they have and have learnt, and for the hard work rhey make, and for the continual work of learning more and more.

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Trial and error mainly!

I agree, most filter makers do exactly that.
However, some filters show a deeper knowledge and understanding in image processing, which makes me believe their authors have studied the subject to some degree in college or university. Obviously, they use Matlab in schools, and not FF, but the basics of image processing are the same.