How can I apply a custom filter function (some lambda) to a 2D image object using SimpleITK?

Question

I need to apply some custom logic to each pixel in each 2D image in a set of images I'm processing, using SimpleITK in python. In the documentation there appears to be UnaryMinusImageFilter which is supposed to be a "general" function filter, but I see no option to provide it with my custom logic. I saw that the corresponding ITK class, has api to provide a functor in C++, but how do I do that in python with SITK (preferably without manually iterating over pixels)?