Bloom

Bloom

Bloom is a post processing effect used to make an image pop by having the bright colors in a seen bleed over there surroundings. this effect is a three/four pass algorithm depending on if the blur is 2 pass or 1. The passes involved are: the bright pass, the blur pass and the composite pass.

http://commons.wikimedia.org/wiki/File:Frangipani_flowers.jpg  -  Original Photo

 

The bright pass is used to make the bright colors in a scene brighter and the dark colors darker. there are plenty of ways that this can be done. I would recommend looking at how photoshops does it's colour levels adjustment.

Bright pass

The next pass is to take the bright pass texture and blur it so that the bright colors will bleed out on to the dark colors.

Blurred image

The final pass is the composite pass which takes the blurred bright pass and puts it onto the original scene giving the Bloom effect.

Bloomed image