# Layers, Alpha & Masks

**Track:** Imaging — beginner / high school — Digital & Generative Imaging — proposed
**Framework / surface:** ij8 Studio (mask painter · remove-bg)
**Level:** Beginner
**Prerequisites:** What Is a Digital Image?

**In one line:** The alpha channel and the mask — the bridge to every edit.

## Theory, aesthetics & inspiration

Beyond red, green, and blue, a fourth channel — alpha — records opacity, letting one image float transparently over another. The mathematics of stacking were formalized by Thomas Porter and Tom Duff in 1984, whose "over" operator defines how foreground and background blend pixel by pixel. A mask is alpha put to work: white reveals, black protects, gray partially veils, isolating exactly where an edit lands. The instinct is older than the computer — the photomontages of Hannah Höch and John Heartfield, born of Dada, cut and recombined fragments into charged new wholes, teaching that meaning often lives in the seam between layers, in the decision of what to show and what to hide.