Painting on the layer thumbnail instead of the mask thumbnail, which permanently alters pixels you meant to hide.
Editing and retouching
Mask
Also called layer mask, image mask or masking. Here is what it means, when it changes what you export, and what people get wrong.
Editing and retouchingRuns on your deviceUpdated 10 August 2026
The short answer
A mask is a non-destructive control that decides which parts of a layer are visible without deleting any pixels. Painted in greyscale, white areas show the layer, black areas hide it and grey areas let it show partially. Edit or discard the mask and the original pixels return untouched.
Updated
The short version
Mask at a glance
| Quick fact | Detail |
|---|---|
| Colour code | White reveals, black hides, grey is partial |
| Destructive | No, the pixels underneath stay intact |
| Common types | Layer, vector, clipping, saved selection |
| Typical depth | 8-bit, 256 levels of visibility |
| Survives in | Layered formats such as PSD and TIFF |
Slide the table sideways to see every column.
Why work with a mask instead of erasing?
Erasing throws pixels away. A mask only hides them, so every decision stays reversible. If a client wants the shoulder line loosened, or the cut-out turns out to be a pixel too tight once it is on a dark background, you paint on the mask rather than starting again from the original photo.
That reversibility is what makes masks the working unit of retouching. You can soften a mask edge, shift it, invert it, copy it to another image shot in the same setup, or apply the same adjustment through several different masks. None of it touches the photograph underneath.
What are the main kinds of mask?
- Layer mask: an 8-bit greyscale channel attached to one layer, painted with brushes or generated from a selection. The everyday workhorse.
- Vector mask: the same idea driven by a Bezier path instead of pixels, so the edge stays crisp at any size.
- Clipping mask: one layer restricted to the shape of the layer beneath it, useful for dropping a texture or colour into an existing cut-out.
- Saved selection: a selection stored as an extra channel in the document so you can reload it later.
- Segmentation mask: the per-object map an AI model produces, typically hard-edged, which then gets refined before use.
How do masks, mattes, alpha channels and clipping paths differ?
These four words get used interchangeably and they should not be. The distinction is mostly about where the data lives and what it is made of.
| Term | What it is | Where it lives | Edge |
|---|---|---|---|
| Mask | An editable visibility control | Attached to a layer in a working file | Hard or soft, your choice |
| Matte | A finished greyscale opacity map | Data handed to a compositor | Continuous, handles hair |
| Alpha channel | Per-pixel opacity saved in the file | Inside the exported image | As fine as its bit depth |
| Clipping path | A vector outline that hides everything outside it | A path object saved with the file | Crisp, resolution independent |
In practice a mask is what you build, a matte is what it becomes when it is treated as data, an alpha channel is where it lands on export, and a clipping path is the vector alternative for hard-edged work.
What people get wrong about mask
Each one is a real failure mode, not a style preference.
Using a pure black and white mask on a soft subject, which gives the stamped-on look of a sticker rather than a photograph.
Saving the result as JPEG or PNG and expecting the mask to still be editable later, when only layered formats keep it.
Forgetting that a mask hides colour rather than removing it, so background spill at the edge is still there waiting to show as a halo.
Questions people ask
Mask, answered
The follow-up questions people search for once they have the definition.
What does inverting a mask do?
It swaps black for white, so everything that was hidden becomes visible and the reverse. It is the quickest way to flip a selection: cut out the background instead of the subject, or select the easier of the two areas and then invert.
Can I move a mask to a different photo?
Yes, and it is a real time saver on a product shoot where every frame is taken in the same position. Drag the mask to the other layer, then nudge and refine. It only works when the framing and the subject position are close.
Why does my mask have a thin bright line around the subject?
The mask is probably a fraction too generous, so it keeps a ring of edge pixels that still contain the old background colour. Contract the mask by around a pixel, feather it slightly, and use a defringe or colour decontamination step to clean the remaining edge.
Is a mask the same as a selection?
No, though they convert into each other freely. A selection is temporary and disappears when you deselect. A mask is stored with the layer, so it survives saving and can be reopened, repainted and reused.
Same cluster
More from the glossary
Neighbouring entries, so every term in the set is one hop from every other.
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