Has anyone created a custom effect for
-ifx option? From a quick look at the Github repo, it seems there is it might be run through the MMAL interface but I have no idea where to get started there.
The custom effects are part of the closed-source GPU firmware which only Raspberry Pi and Broadcom engineers can change. You can add further effects in post-processing (on the CPU) though.
FWIW, @flakeshake is right that it's a closed source system, but it does seem possible to run your own GL shaders within the
raspistill system by modifying and building your own version from the source files. It does also seem possible to use GL shaders elsewhere for faster image processing, such as this example which may be helpful to others.