While image editing in Photoshop can be straight forward, it is also very easy to run into the dilemma of digital image interpolation. You may be surprised how often image interpolation occurs in the average editing workflow. 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 any adjustment directly to an image, the software, in this case Photoshop, has to guess where pixels need to be placed in the new modified (resized, flipped, altered) image. The computer has to now guess where the pixels will be placed in the modified image. And with guesswork comes data loss which can be the beginning of a detrimental slippery slope of image errors. By making changes through the Levels Adjustments, the new modified image is now of a lesser quality than the original—sometimes untraceable to the eye.

However, if manipulation after 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, this permanent damage impacts the pixelation 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 develop. When that occurs, it does become visible to the eye and is especially apparent in print (or web) output.

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

Adjustment Layers are the answer to non-destructively manipulating your image. By creating a New Adjustment Layer, you can avoid altering the original image information. Using the Adjustment layer, the edits occur on a different layer, separated from the original image. Plus, you save your adjustment layer to just your specifications, all the while protecting your original image and 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. With regards to saving the adjustment layer, it 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

Using adjustment layers, allows for more flexibility in your photo editing, will which save you time, effort, and perhaps money!