was this a serious question about what's the box supposed to be?
...I made an object shader with self illumination support for ratchet an I thought using his box is a great way to test my bloom shader

EDIT: the blending seems to be okay now
...some more screens:



EDIT#2: Just made an fps test
600fps - which is pretty fast!
compared to my old bloom shader (which was less complex and looked worse) this is a huge improvement (~5x faster)