Forward and Back
As long as the device used to collect the image information (scanner, digital camera, and so on) is not defective or otherwise prone to collecting bad image information, Levels will accomplish most basic correction tasks. Coupled with other simple-to-use color enhancement tools (like the Color Balance) will help you make quality adjustments without getting steeped in complex techniques and voluminous theory.
Making changes with the Levels sliders is actually the same as using a simple 3 point curve. When you get good at simple Levels corrections then it will be time to start exploring Curves. Curves will allow you to make corrections similar to the Levels technique, while simultaneously correcting for specific color casts Ñ all in one shot. However, you need to understand the idea of correction and should be reasonably confident about the view of your images onscreen. It also doesn't hurt to have confidence in your ability to use Color Samples. Curves may end up causing more trouble than they solve if you jump in willy-nilly.
If you aren't clear about any of the techniques or ideas discussed here, you can find out more in Special Edition Using Adobe Photoshop 6.
Evaluating Image Color: p. 409Ð444
Tonal Correction: p. 445Ð464
Color Correction: p. 465Ð484
Calibrating your Monitor: p. 414Ð419
Histogram Evaluations: p. 433Ð442
Color Conversions: p. 485Ð511
Applying Blend If: p. 514Ð517
Using Image Histories: p. 251Ð262