premultipliedalpha

Premultiplied alpha is a technique used in computer graphics to represent color and transparency information. In this method, the color channels (red, green, blue) are multiplied by the alpha channel value before being stored. This means that a fully transparent pixel will have its color channels set to zero, regardless of their original intended color. For example, a transparent red pixel would be represented as (0,0,0,0) instead of (1,0,0,1) or (255,0,0,255) in a standard, non-premultiplied alpha representation.

This approach simplifies certain rendering operations, particularly blending. When combining two premultiplied alpha images, the mathematical operations are straightforward and less prone to artifacts, such as dark edges appearing around semi-transparent objects, which can occur with non-premultiplied alpha. When rendering an object with premultiplied alpha, the color values directly represent how much of that color is "mixed" with the background due to its transparency.

The primary advantage of premultiplied alpha lies in its efficiency and quality during alpha blending. It is widely adopted in various graphics pipelines, including those used in operating system UIs, game engines, and image editing software. However, it can be less intuitive to work with directly, as the color values are not the "true" colors of the object but rather the colors as they would appear when blended against a black background. Conversion between premultiplied and non-premultiplied alpha formats is a common task when integrating assets or working with different software.