Okay so I was able to mitigate this issue by:
- Summing 4 taps on the first 2 down samples
- Then blurring on the subsequent down samples as Hodgman suggested
- Then composting 4 layers of bloom from the various levels (Up sampling the lower resolution ones a few times to mitigate the blockiness)
It actually takes a lot of tweaking to try and get a nice blur...
Does anyone have any advice on how to achieve a good inverse square falloff on the bloom?
So far I'm just tweaking and weighting each composite layer as well as number of iterations and sigma on blur at each layer by eye.
Here's the result from a 1 pixel bloom so far... Not quite as nice as I want but getting there..