Non-Destructive Editing in Photoshop: Part 1
What is non-destructive editing?
To understand non-destructive editing, it helps to first define destructive editing. A destructive edit is any change made in a Photoshop file that actually modifies or deletes the original image data. These are permanent edits. Of course, you can always "Undo" while you're working, but if you save/close the file and come back to it later destructive edits are set in stone.
If you paint part of a photo red with the brush tool, those pixels are now red. The original image data is gone, never to be heard from again. That is an example of destructive editing and it's bad news.
Wouldn't it better if there was a way to keep edits flexible and preserve that original image data in case you want to make adjustments or remove edits later? That is where non-destructive editing comes in. With non-destructive editing in photoshop, you never overwrite or remove the original image data and all changes can be fine-tuned or undone at any point in the future. You can always revert to the original image data. Non-destructive editing is how professionals work and you will learn to love it.
When should I use non-destructive editing?
If you've ever opened photoshop, you learned pretty quickly that there are multiple ways accomplish almost any task. For example: if you want to convert an image to black and white, you could convert the file to grayscale, you could use a black and white adjustment layer or any of about a half-dozen other methods. Each of these techniques may have different pros and cons, but as a general rule every edit should be done non-destructively if at all possible.
You can always flatten a file later, but you can't always recover from destructive editing techniques. Editing destructively is playing with fire and can lead to lost work, wasted time and even permanently ruined images if you don't make copies of your original files.
How to crop an image non-destructively.
One of the quickest ways to trash a ton of image data is to crop an image. Normally, once an image has been cropped, everything outside the visible area is completely deleted. If you come back to your file later and want to expand the crop that you've made, you're out of luck and would have to start over from the original image.
There is a better way and it's stupidly easy. Once you've opened a file, the first step is to convert the background layer into a normal layer. Hold the Alt Key and double click on the background layer.
Now select your crop tool from the toolbar or hit "c" on your keyboard to activate the crop tool.
Drag across your image to frame your crop how you want it.
Before you hit enter, make sure the radio button for "Hide" is selected. "Delete" will do just that, completely removing the pixel data.
I am using Photoshop CS5. If you're up to date on CS6, you will want to make sure the box labeled "Delete Cropped Pixels" is not checked in order to get this same result.
Now press Enter on your keyboard. The crop will be applied, but the image data is still there in case you want to make adjustments.
Try dragging a new crop to recover part of the area that you removed from the image before.
Hit Enter and, viola, the pixels are unhidden.
Using this technique will allow you to always adjust your photo crops infinitely. You can even revert back to the original version if you want.
Congratulations, you've taken you're first step toward a non-destructive photoshop workflow. Not so bad, was it?