Transparency / Alpha Transparency
The ability of an image to have pixels that are partially or fully invisible, allowing backgrounds to show through. Supported by PNG, WebP, GIF (1-bit only), and AVIF — but NOT by JPEG.
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Transparency in digital images means certain pixels are partially or fully invisible — rather than being a colour, they allow whatever is behind them (a web page background, another image, or a colour) to show through.
How Transparency Works
Transparency is stored in an alpha channel — an additional data channel alongside the Red, Green, and Blue (RGB) channels. The alpha channel stores a value from 0 (fully transparent) to 255 (fully opaque) for every pixel.
- Full transparency (alpha = 0): Pixel is invisible
- Full opacity (alpha = 255): Pixel is solid
- Semi-transparency (alpha = 1–254): Pixel is partially see-through
Which Formats Support Transparency
| Format | Transparency Support |
|---|---|
| PNG | Full alpha transparency ✅ |
| WebP | Full alpha transparency ✅ |
| AVIF | Full alpha transparency ✅ |
| GIF | 1-bit only (on or off — no partial transparency) |
| SVG | Full transparency ✅ (vector) |
| TIFF | Alpha channel supported ✅ |
| JPEG | ❌ No transparency support |
| BMP | Limited — 32-bit BMP supports alpha |
Why JPEG Cannot Be Transparent
JPEG's compression algorithm is designed specifically for photographs and does not include an alpha channel. When you save a transparent PNG as JPEG, transparent pixels are replaced by white (or whatever background colour the exporter uses).
Use Cases
- Logos on websites — PNG with transparency sits on any background colour
- Watermarks — semi-transparent PNG overlay on photos
- Stickers and cutout images — transparent background in product photos
- Icons — transparent ICO files for Windows application icons