Help Understanding Curves?

[backygirly]

Can anyone explain the process of using Curves? I understand the basic idea of setting a white point and a black point, but that little graph in the middle blows my mind. I'm confused!

[charles]

Im looking forward to reading the serious answers to this question as I only have a vague idea myself.
I think the curves allows us to adjust certain ranges of highlights and shadows and every range in between. ie if you need to brighten only the very darkest shadows or darken the brightest highlights then curves should do the job.
Best Wishes
Charles

[Doug Nelson]

The curve is a visual representation of the relationship between the tonal values of the current image and the adjusted image. With no changes made there is a 1:1 relationship, so the curve is straight. Changes of a value to lighter or darker will cause that point on the curve to raise or lower.

Additionally (and more importantly), the curve represents the contrast between tones in an image. The steeper the curve, the more contrast (technically known as the 'gamma', but don't let that confuse you).

If you click and drag on your original image while watching the curves dialog you can actually see the value slide up and down the curve as you pass over lighter and darker tones. Ctrl-clicking on the image will install that value point on the curve.

[DannyRaphael]

backygirly and charles:

Welcome to RetouchPRO! Always enjoy seeing new folks.

The concepts of curves (and levels) aren't all that difficult to comprehend nor is how to use them effectively, but trying to give a short answer about the ins-and-outs is very difficult, if not impossible.

Here are a couple pretty good tutorials on the subject you might want to browse to help fill in the gaps. The third one talks about the differences between Levels and Curves, a frequent source of confusion:

http://www.luminous-landscape.com/tu...d_primer.shtml

http://www.gurusnetwork.com/tutorial...p/curves1.html

http://www.apple.com/creative/resour...605curves.html

If you can get your hands on a copy of Adobe Photoshop Master Class by John Paul Caponigro, there's a section that IMHO is one of the best I've ever seen at explaining curves (conceptually) as well has how to intrepret typical curve patterns and (from a correction standpoint) what to do about "bad ones."

Before you know it, you'll be curves experts! Hope this helps and, again, welcome.

~DannyR~