Traditional photo editing is ‘destructive’. That means every adjustment you make permanently changes the pixels in the photo and there’s no way back unless you’ve saved a copy of the original and you’re willing to start again.
‘Non-destructive’ editing is fully reversible. You can go back and undo or redo all of your editing work at any point in the future. This is the approach used by the latest all-in-one photo cataloguing, RAW processing, editing and effects tools.
In between, many traditional photo editors like Photoshop and Affinity Photo, for example, offer a semi-non-destructive approach where they still make permanent changes to the pixels in the photo but record a ‘history’ of all your changes that lets you backtrack to an earlier state. You may also be able to save ‘snapshots’ of particular stages that you want to go back to for comparison, say.
Many programs like Photoshop also offer ‘adjustment layers’. These simply alter the appearance of the image below the layer without changing its pixels. You can use adjustment layers for curves and levels adjustments, hue/saturation adjustments, black and white conversions and more.
Adjustment layers are much closer to true non-destructive editing because they are storing processing instructions, not modifying the image directly. These instructions are stored as ‘metadata’ within the image file. One of the issues with non-destructive editing is that this processing metadata must be stored in some way within the image or alongside it, and we’ll come back to this.
There are now many fully non-destructive photo editors, mainly cataloguing software like Adobe Lightroom, Capture One, Skylum Luminar, Alien Skin Exposure X, ON1 Photo RAW and DxO PhotoLab (DxO PhotoLab is not quite a cataloguing tool, but the non-destructive editing principle is the same).
None of these programs make any changes to the original image file. They all save your editing adjustments as metadata, even after you’ve closed the image and quit the software. They don’t create additional image files to take up extra space on your computer.
This has advantages beyond just space-saving. Many of these programs let you create additional ‘virtual’ versions of a single image. In Lightroom, for example, they’re called ‘Virtual copies’ and in Capture One they’re ‘Variants’. This means you can experiment with multiple creative interpretations of the same image file without physical duplication, and all fully adjustable at any point in the future.
Non-destructive processing is especially useful for editing RAW files. These can’t actually be editing directly, so the traditional approach would mean having to process the RAW file into a JPEG or TIFF file before being able to edit it. This means making initial decisions about the RAW processing which can’t be reversed later.
Fully non-destructive programs don’t have this limitation. You can ‘edit’ a RAW file just as easily as a JPEG or a TIFF image, with no need to ‘process’ it first, and while retaining access to all the data in the original RAW file.
Non-destructive editing has also led to a boom in the market for ‘presets’ – sets of adjustments you can apply with a single click. Being non-destructive, these preset effects can be removed, altered or replaced at any time.
But it’s important to remember these non-destructive adjustments use metadata that has to be stored somewhere. In Photoshop or Affinity Photo, it’s stored in these programs’ bespoke file formats. In fully non-destructive programs like Lightroom, it’s stored either in the image catalog file or as ‘sidecar’ files alongside the image (Lightroom can do both).
Some programs rely fully on these sidecar files, some offer both approaches. When you use DxO PhotoLab or Alien Skin Exposure X, for example, you’ll see small sidecar files appearing in your image folders alongside your photos. It’s important that these are kept together – the sidecar files contain the processing instructions, and if they get separated, your editing changes are lost.
This is one of three principal weaknesses with non-destructive editing:
1) Your adjustments are proprietary – they will only make sense within the program you used, so that Capture One will ignore any adjustments you made in Lightroom, for example. In short, for all its advantages, non-destructive editing does tend to lock you into a single software solution.
2) Your adjustments have to be stored somewhere. This is either in a central image catalog, which leads to the possibility this may become disconnected from your original source images (if you move or modify them outside the program, say) or in sidecar files which can also become separated from the original photos.
3) Images edited with non-destructive tools are not ‘finished’ until you ‘export’ them. You may get an image looking just how you like it in Lightroom, but it won’t look like that anywhere else until you export a new, processed version as a regular JPEG or TIFF image. This applies across all non-destructive photo editing programs.