Alpha channel (transparency)
Also known as: transparency channel, image transparency, alpha transparency
An alpha channel is the part of an image that records transparency — how see-through each pixel is. It lets formats like PNG, WebP, and GIF place a subject over any background. JPEG has no alpha channel, so it cannot store transparency.
- Records how transparent each pixel is
- Supported by PNG, WebP, TIFF; not by JPEG
- Adds data, so transparent files are larger
How transparency is stored
Alongside the red, green, and blue color channels, an alpha channel adds a value for each pixel that ranges from fully opaque to fully transparent. A full 8-bit alpha allows soft, partial transparency, so edges and shadows blend smoothly instead of looking cut out.
Formats differ in what they support. PNG, WebP, and TIFF offer full alpha; GIF allows only on/off transparency, which causes jagged edges; JPEG has none at all, which is why a transparent design saved as JPEG gets a solid background.
Transparency and file size
Storing an alpha channel adds data, so a transparent PNG is typically larger than the same image as a flattened JPEG. When you do not need transparency, a JPEG or flattened export saves space.
To create transparency, you remove or knock out a background and export to a format that supports alpha — saving back to JPEG silently discards it.