Definition
Two transparency models for web images: binary transparency (pixel fully opaque or fully transparent) in GIF/PNG-8, and alpha transparency (256 opacity levels per pixel) in PNG-24/32 and WebP.
Why It Matters
Understanding how alpha channels work is the key to creating sophisticated, layered visual designs on the web and in software. This technical concept is what allows for smooth blending, complex overlays, and the “polished” look we expect from modern user interfaces.
Core Concepts
- Binary Transparency: On/off per pixel; soft edges require a matte color baked in.
- Halo Effect: Binary-transparent PNGs on wrong background show jagged fringe.
- Alpha Transparency: Smooth edges, drop shadows, and glows work on any background.
- Production: Export alpha PNGs when graphics overlay variable backgrounds.