You can choose whom to affect when you channel energy.
Prerequisite: Cha 13, channel energy class feature.
Benefit: When you channel energy, you can choose a number of targets in the area up to your Charisma modifier. These targets are not affected by your channeled energy.
Normal: All targets in a 30-foot burst are affected when you channel energy. You can only choose whether or not you are affected.
Do I have to be able to see a creature in order to exclude them from the effect of my channeled energy?
Just like using a Target: creature spell, you must be able to see or touch a creature to affect it (or, in the case of this feat, select it to be unaffected). Pinpointing the square of an invisible creature isn’t sufficient—you must be able to see or touch the creature. Note that this works differently than an alchemist‘s precise bombs discovery, which allows the alchemist to exclude *squares* from his bomb’s splash area (not targets).
Pathfinder RPG Core Rulebook. Copyright 2009, Paizo Publishing, LLC; Author: Jason Bulmahn, based on material by Jonathan Tweet, Monte Cook, and Skip Williams.