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Layer Mask Properties and Operations

Every mask command, and when to use it

In This Lesson

Adding a Mask: The Options

Right-click a layer and choose Add Layer Mask (or Layer → Mask → Add Layer Mask). The dialog offers several starting states, and picking the right one saves work:

Initialize mask toResultUse when
White (full opacity)Everything visible; paint black to hideYou'll hide a few areas
Black (full transparency)Everything hidden; paint white to revealYou'll reveal only a little
Layer's alpha channelMask matches existing transparencyConverting alpha to an editable mask
SelectionSelection becomes the maskYou've already made a selection
Grayscale copy of layerMask = the layer's luminosityLuminosity-based blends

💡 Black vs. White Start

Reveal a small subject on a big layer? Start with a black mask and paint it in. Hiding a small area? Start white. Choosing the start that means less painting is a small habit that saves real time.

Editing vs. Viewing the Mask

Click the mask thumbnail in the Layers dialog to edit the mask; click the layer thumbnail to edit the image. A white border shows which is active — a constant source of confusion, so glance at it before you paint. Two view helpers, on the mask's right-click menu:

  • Show Layer Mask — displays the mask itself (grayscale) on the canvas so you can see exactly what it looks like.
  • Edit Layer Mask — toggles whether painting affects the mask or the layer.

The Mask Operations Menu

Right-click the layer (or Layer → Mask →) for the full command set:

  • Disable Layer Mask — temporarily ignore the mask to preview the full layer. A red border marks a disabled mask.
  • Apply Layer Mask — bakes the mask into the pixels permanently (the layer keeps only what the mask showed). Use only when finished.
  • Delete Layer Mask — discards the mask, restoring the full layer.
  • Mask to Selection / Add / Subtract / Intersect with Selection — turn the mask back into a selection.
flowchart LR A[Layer mask] --> B{What next?} B -->|Preview full layer| C[Disable mask] B -->|Reuse as selection| D[Mask to Selection] B -->|Finalize| E[Apply mask]

Disable to preview, convert to reuse, apply only when done.

Mask ↔ Selection

Masks and selections are the same grayscale data in different forms, and you can convert freely. Mask to Selection turns a mask into marching ants; adding a mask initialized to a selection goes the other way. This round trip is the backbone of a real workflow: make a selection, turn it into a mask, refine it by painting, then convert it back to a selection to reuse on another layer or adjustment.

Moving and Copying Masks

  • Reuse a mask on another layer: click the mask, Ctrl+C, select the target layer's mask, Ctrl+V, and anchor.
  • Move mask independently of the layer: by default the mask moves with its layer; unlink them (click the chain icon between the thumbnails) to slide the mask alone.
  • Invert a mask with Colors → Invert while the mask is active — instantly swaps what's hidden and shown.
  • Soften a mask with a Gaussian blur for feathered edges you can re-tune.

⚠️ Don't Apply Too Early

Apply Layer Mask is permanent — it discards the mask and the hidden pixels. Keep masks live for as long as possible; only apply (or better, keep the XCF and export a flattened copy) when the composite is truly finished.

Practice Activities

  1. Start smart. Reveal a small subject using a black-initialized mask, then hide a small area using a white one — feel the difference.
  2. Round trip. Make a selection, add it as a mask, refine by painting, then Mask to Selection and reuse it on an adjustment.
  3. Copy a mask. Build one mask and copy it onto a second layer so both share the same boundary.

Summary

✅ Key Takeaways

  • Choose the mask's starting state (white, black, alpha, selection, grayscale) to minimize painting.
  • Watch the active thumbnail border — edit the mask or the layer deliberately.
  • Disable to preview, Mask to Selection to reuse, Apply only when finished.
  • Masks and selections convert freely — the core of a flexible workflow.
  • Copy, unlink, invert, and blur masks; keep them live as long as possible.

➡️ What's Next

Next, the transparency that underlies masking: Alpha Channels and Transparency.

Additional Resources