I can't resist posting this ... even though it is available through a link in a previous discussion about the Dodge and Burn Tone Tools.

The introduction states:

"This is a long one. For your own comfort and safety, please insure an adaquate quantity of nourishment and caffinated beverages; please designate a trusted loved one to force quit the computer if you’re not out by tomorrow …"

Lol ... not that long really, only 3 ... 3 pages of what I consider to be INVALUABLE information regarding this function of image editing and post work.

Here you go ... Curves Command.

Did I mention ... INVALUABLE??

:o)