Go to the discussion in this thread. Go back a few posts.
A few posts? There is now 128 posts on that thread and growing...lol I want to know to what it is...I don't use Photoshop I use PSP and I have no idea what it is.
What Jak said is true, ofcourse. If you were wondering about the terms, they come from darkroom developing. Exposing a certain area of the photo either less or more when working with the enlarger; the photoshop tools replicate that effect.
