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OpenGPEX 1.x documentation (legacy editor).

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Masks & Non-Destructive Editing

Masks allow you to hide or reveal parts of a layer without permanently deleting any pixels. This is one of the most powerful concepts in non-destructive editing.

Understanding Masks

A mask is like a stencil applied to a layer:

  • White areas = fully visible (content shows through)
  • Black areas = fully hidden (content is invisible)
  • Gray areas = semi-transparent (partially visible)

The key advantage: your original image data is never modified. You can always restore hidden areas.

Mask Types in OpenGPEX

Bitmap Masks (Painted)

Created by painting with the Eraser tool. Erasing hides content; the Restore tool (Tab) reveals it again. Hold Cmd/Ctrl and click to start an additional, separate mask on the same layer.

Vector Masks (Shape-based)

Geometric masks (rectangle, ellipse, or path) that constrain the visible area of a layer. Each supports:

  • Inversion: Swap visible/hidden regions
  • Feathering: Soft, graduated edges (radius in pixels)
  • Enabled toggle: Temporarily disable without deleting

Note: In v1, vector masks are created automatically by editing operations (e.g. Peel/cut punches a "hole" vector mask into the source layer; Union Merge combines fragment hole masks). There is no dedicated "draw a vector mask" tool.

Using the Eraser as a Mask Tool

The Eraser in OpenGPEX is fundamentally a mask painting tool:

Erasing (Hiding) Content

  1. Select the layer you want to mask
  2. Press E to activate the Eraser
  3. Paint over the areas you want to hide
  4. Adjust Size, Opacity, and Hardness for control

Restoring (Revealing) Content

  1. Press Tab while the Eraser is active to switch to the Restore tool
  2. Paint over previously erased areas to bring them back
  3. This paints white (opaque) back into the mask, revealing original content
  4. Press Tab again to switch back to Eraser
  5. Hold Cmd/Ctrl and click to create a brand-new mask on the layer

Partial Transparency

  • Use lower Eraser opacity (e.g., 30-50%) to create semi-transparent areas
  • This is perfect for gradual fade effects

Vector Mask Properties

Property Description
Shape Rectangle, Ellipse, or freeform Path
Inverted When enabled, the area inside the shape is hidden (outside is visible)
Feather Blur radius for soft edges (in pixels)
Enabled Toggle the mask on/off without deleting it

Practical Mask Workflows

Isolate a Subject

  1. Use AI Background Removal for initial isolation (see AI Tools)
  2. Refine edges with the Eraser tool at a small size
  3. Press Tab to switch to Restore tool for any accidentally removed areas

Create a Vignette

  1. Select your image layer and activate the Eraser (E)
  2. Use a large, soft brush (low hardness, e.g. 0-20%) with moderate size
  3. Paint around the edges of the image to fade them out toward the border

Blend Two Images

  1. Stack two images as layers
  2. Use the Eraser with a large, soft brush (low hardness) on the top layer
  3. Paint to gradually reveal the bottom layer for a natural blend

Tips

  • Masks are fully undoable — use Ctrl/Cmd + Z to step back
  • Each layer can have multiple masks applied simultaneously
  • Bitmap masks are stored as separate assets, not embedded in the original image
  • You can disable a mask temporarily without deleting it

Next Steps

Last updated: 2026-07-30