Understanding curves option of colors in GIMP?

Question

I started using GIMP recently, and came across an option called Curves under the Colors menu. What is the significance of it and how to use it correctly.

I get some good colors if I make a graph in 'S' shape. But what exactly is the meaning of it? How do I use this tool to enhance my photographs?

Answer

The GIMP's curves tool is virtually identical to PhotoShop's Curves tool. Almost all photo manipulation tools have a way of doing that action. There are a number of good explanations of it out on the internet if you look for photoshop: http://www.google.com/search?hl=en&q=curves+adjustment+in+photoshop

this one however is fairly thorough in it's explanation of what it's doing: http://www.cambridgeincolour.com/tutorials/photoshop-curves.htm

(disclaimer, it's been a good 3 years since I've used the GIMP, it's possible they've changed it since then, but I highly doubt it since the curves tool is one of the more fundamental advanced editing tools.)

Check more discussion of this question.