Implementing custom non-linear 2D filter in OpenCV

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Hi! I see that there is an implementation path for custom linear filters, but not non-linear 2d filters. OpenCV provides a lot of the common nonlinear filters themselves, but would it be correct to assume that if I wanted to use my own nonlinear equation I would need to create the kernel function myself? I am currently using CUDA to make my kernels so I could just continue using my own in these cases, but I am somewhat new to optimization of cuda kernels.