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What is Image Masking?

Image masking uses binary, grayscale, or alpha values to control which pixels of another image are visible or affected by an operation. Intermediate mask values permit partial coverage and soft transitions.

How Image Masking works

A mask participates in compositing as a coverage field: its samples modulate source opacity or limit where an effect is evaluated. Raster masks follow the image grid and can describe hair or soft shadows, while vector clipping paths are rasterized into coverage at the requested output size. Compound vector paths can include holes according to fill and path rules. Masks enter media workflows during cutout creation, selective correction, layout, and final compositing.

Key facts

  1. Premultiplied color requires consistent alpha handling; filtering straight and premultiplied representations as if they were the same can create dark or bright fringes.
  2. A clipping path describes geometric inclusion and can scale without a fixed pixel grid, but feathered translucency generally requires rasterized coverage or an alpha mask.
  3. Mask and source must share a coordinate transform, dimensions, and polarity; silent resizing or inversion can shift the cutout or expose the intended background.

When Image Masking matters

Use raster masks for detailed or soft-edged selections and vector paths when boundaries must scale cleanly or remain editable. Incorrect polarity, alignment, or alpha interpretation can hide the intended subject or create visible seams.

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