This was the core premise of your original comment!

I'm not sure how you define algorithms, but I have a feeling it's not a universal definition. I would argue that diffusion is an algorithm like HDR compensation. Both describe well defined and repeatable processes that can be broken down into low-level components with different potential implementations.

How does your HDR algorithm select a exposure curve for tone-mapping? How does it handle noise rejection? Does it apply any non-local corrections or smoothing? Does the existence of these questions mean that HDR is less of an algorithm? Where do we draw that line?