Every edit should still be undoable next week

The mistake that ends the job

You open the photo, brighten it, warm it, crop it, flatten it, save the JPEG over the original and send it. The client says: lovely, slightly darker, and can we see it uncropped.

Now you are stuck. The cropped-away pixels are gone. The tonal range you stretched is gone. Every further edit is applied to the damage.

Non-destructive editing is the discipline of never modifying original pixels — only stacking instructions on top of them. It is not a preference for tidy people. It is what makes a second revision cost thirty seconds instead of an afternoon.

The four mechanisms

Adjustment layers. A Curves or Hue/Saturation layer sits above the photo and changes how it is displayed, not what it contains. Double-click it a week later and the sliders are exactly where you left them. In Photoshop: the half-filled circle at the bottom of the Layers panel. Photopea, Krita (it calls them *filter layers*) and Affinity Photo all have the same thing in the same place.

Layer masks. A greyscale channel attached to a layer that decides where it shows. That is the next lesson, and it is the important one.

Smart objects. Right-click a layer, *Convert to Smart Object*. Now the original is stored inside a container. Scale it down to 20 per cent and back up and it comes back sharp, because the resize is a display instruction applied to the stored original rather than a resampling of what is on screen. Filters applied to it become re-editable *smart filters*. Photopea supports smart objects. Affinity has an equivalent in its live filter layers.

Parametric editors. Lightroom, Capture One, and the free darktable and RawTherapee never write to your file at all. They record a list of edits in a sidecar and re-apply it every time you open the image. This is the most non-destructive model there is, and it is why serious work starts in a raw developer and moves to a pixel editor only for things a slider cannot do.

What each editor actually gives you

The money question. Photoshop is named in job adverts, so learn its vocabulary. But for this particular set of features:

• Photopea (photopea.com) runs in a browser tab, is free with advertisements, and opens and saves layered PSD. It has adjustment layers, layer masks, smart objects, Curves, blend modes. For non-destructive work it is genuinely equivalent to Photoshop for most jobs. Honest limits: everything lives in your browser's memory, so a 40-layer 100-megapixel file will crawl or crash; its colour management is thin, which matters for print; and it is maintained by essentially one developer, which is remarkable and also a risk.
• GIMP has excellent layer masks and channels and, since version 3.0 in early 2025, non-destructive layer effects. It still has no true adjustment layers, so a Curves change is usually baked into a duplicated layer. That is a real gap, and the workaround — duplicate, adjust, mask — costs you re-editability.
• Krita has filter layers and filter masks and is fully non-destructive. It is built for painting, so its photo-retouch tools are thinner. Excellent on a drawing tablet.
• Affinity Photo has adjustment layers, live filters and a fast engine. It was a one-off purchase of roughly £70 with no subscription; after Canva bought Serif the app was relaunched free of charge in late 2025 with some newer features tied to an account. That corner has moved twice already, so check the current terms rather than trusting this paragraph.
• On a phone: Snapseed keeps every edit as a re-editable *stack* you can reopen and change, which is real non-destructive editing on a device that costs nothing extra. Lightroom mobile's free tier is parametric by design.

More on picking between them in choosing your tools.

The file discipline that costs nothing

• Save the layered working file first, before you export anything. PSD in Photoshop and Photopea, XCF in GIMP, KRA in Krita, AFPHOTO in Affinity. The JPEG is a delivery format, never a working one.
• Name versions. sandal-front_v3.psd, not final_final_2.psd. You will need v2 back.
• Never save a JPEG over a JPEG. Every save re-compresses what the last one already damaged.
• Keep the camera original in a folder you do not edit in.

What this does not save you from

Non-destructive is not infinite. Three honest limits.

Bit depth still bites. An 8-bit file has 256 levels per channel. Stretching it hard leaves gaps between them, and gaps show up as banding in skies. Adjustment layers delay the damage until you flatten, but they do not create data. Work in 16-bit — Image > Mode > 16 Bits/Channel — for anything with a big tonal stretch.

The file gets heavy. A 30-layer smart-object stack can be a gigabyte and slow on an old laptop. Rasterise the parts you have genuinely finished.

Someone else has to open it. A PSD full of smart filters opens correctly in Photoshop and Photopea and only approximately in GIMP. If you are handing off, also export a flattened TIFF.

Today: open your last edited photo. If there is no layered file next to it, you did the work twice already and do not know it yet.