Professional Photoshop Work Flows Techniques
Adjustment Layers

The main goal of digital color imaging is to CAPTURE as much color information as possible, and to PRESERVE that color information throughout the editing processes.

That said, nothing is more damaging, destructive to color information than editing it.

Whether we do the editing, color correcting, image adjustments in Photoshop's Curves, Selective Color, Levels, Channel Mixer, Hue/Saturation, or Color Balance — we need to develop strategies of high–bit CAPTURE and least–destructive color PRESERVATION.

The high–bit, 16–bit scanning Workflow and Adobe's Camera RAW Photoshop plug-in provide high–bit capturing methods, but this how to tutorial is about the least–destructive editing methods, specifically, Photoshop's Adjustment Layers.

The first "rule" to learn is:

You move (in Photoshop), you lose (information you cannot get back).

We can witness this fact first hand in Photoshop's Levels, Histogram:

Original Capture: Notice the full (healthy) continuous black area — this is what we want.
A Minor Gamma Correction center slider moved (to slightly lighten the image).
Edit Applied: Notice the gaps of missing information and degraded height, the file is actually missing color information in those empty levels — this is what we want to avoid.

In a digital image, those holes, blanks, gaps, missing areas represent posterization in the image.

Make a couple more minor Edits — outside of Adjustment Layers — and it is easy to see how quickly even slight moves add up in Photoshop to significant image degradation.