How to use Adjustment Layers in Photoshop

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When editing an image in Photoshop, it is very easy to run into the problem of digital image interpolation. You may be surprised how often interpolation occurs. Any time you resize (enlarge, compress, contract), resize, remap (rotate, flip), or resample an image, interpolation occurs.

What is digital image interpolation?

When you make an adjustment to an image, the software has to guess where the pixels would normally be placed in that new modified (resized, flipped) image. And with guesswork comes mistakes, errors, and data loss. The new modified image is now of a lesser quality than the original-sometimes untraceable to the eye.

However, if manipulation upon manipulation occurs (generations of changes), the result will soon be poorer quality images, and hence is considered destructive to the original image. When you make edits via the Levels adjustment then this destruction will always occur. Worse yet, these changes are permanent to the pixels and the missing information (the data the software had to "guestimate"), is gone forever.

If enough of these destructive adjustments occur, banding (also know as posterization) begins to take place, which is when there is too little information spread too far apart and a rough transition between colors or tone develops. When that occurs, it does become visible to the eye and is especially apparent in print (or web) publications.

So, how can we avoid interpolation and create non-destructive image adjustments?

Adjustment Layers are the answer to creating non-destructive image adjustment. By creating a New Adjustment Layer, you can avoid altering the original image information. The edits occur on a different layer, separated from the original image. Plus, you can edit your adjustment at any time without losing all your subsequent work.

By creating a layer mask, you will never truly alter the original image, because the layer mask is being applied to the individual adjustment.

Better yet, you can save your work and any adjustment you've made. The adjustment layer will not revert back to zero, and it will stay the same using the latest information you've applied to it.

There are 12 adjustments (presets) that Photoshop offers:
-- Levels
-- Curves
-- Color Balance
-- Brightness/Contrast
-- Hue/Saturation
-- Selective Colors
-- Channel Mixer
-- Gradient Map
-- Photo Filter
-- Invert
-- Threshold
-- Posterize

If you need more flexibility in your photo editing, use adjustment layers.

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