##What is NDVI? What is NRG?##

What are these images we're trying to make? What do they tell us about vegetation, and why? These diagrams should help to understand what it is we're doing and why these are good ways to analyze plant life.

<a href="https://www.flickr.com/photos/jeffreywarren/5396083342/" title="What is an NDVI image? by jeferonix, on Flickr"><img src="http://farm5.static.flickr.com/4090/5396083342_905507e190.jpg" width="500" height="375" alt="What is an NDVI image?" /></a>

<a href="https://www.flickr.com/photos/jeffreywarren/5396083368/" title="What is an NRG image? by jeferonix, on Flickr"><img src="http://farm5.static.flickr.com/4139/5396083368_8d8e441daa.jpg" width="500" height="375" alt="What is an NRG image?" /></a>

<a href="https://www.flickr.com/photos/jeffreywarren/5396083328/" title="Why do NRG and NDVI images work? by jeferonix, on Flickr"><img src="http://farm6.static.flickr.com/5095/5396083328_54cdca5fbc.jpg" width="500" height="374" alt="Why do NRG and NDVI images work?" /></a>