Quick answer

Image transparency stores how opaque each pixel should appear. Fully transparent pixels reveal the background, while partial transparency blends the image with what is behind it.

Original example

One badge over two colors

Place the same soft-edged badge over white and navy backgrounds. Its transparent outer pixels reveal each background, while partially transparent edge pixels blend smoothly into both.

The alpha channel

Formats with alpha support can store an opacity value alongside color values. An alpha value can describe a fully opaque, fully transparent, or partially transparent pixel.

JPEG does not provide normal alpha transparency, while PNG can store full alpha transparency.

Common misunderstandings

  • A white background is not the same as a transparent background.
  • A checkerboard shown by editing software is usually a preview convention, not part of the saved image.

Related answers

Sources

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