What does rgba mean?

rgba refers to the color space of Red (red), Green (green), Blue (blue) and Alpha. rgba is sometimes described as a color space, but it is really just an rgb model with additional information attached.

RGBA refers to the color space of Red (red), Green (green), Blue (blue) and Alpha. Sometimes rgba is described as a color space, but it is really just the rgb model with additional information appended.

The color used is RGB and can belong to any RGB color space, but Catmull and Smith proposed this indispensable alpha value between 1971 and 1972, making alpha rendering and alpha synthesis possible. The proposer named it after alpha because the classical linear interpolation equation αA (1-α)B uses this Greek letter.

The alpha channel is generally used as the opacity parameter. A pixel with an alpha channel value of 0% is completely transparent (i.e. invisible), while a value of 100% means a completely opaque pixel (traditional digital image).

A value between 0% and 100% causes the pixel to show through the background, like through glass (translucency). This effect is simple binary transparency (transparent or opaque) can't be done. It makes digital compositing easy. The alpha channel value can be expressed as a percentage, an integer, or as a real number from 0 to 1 like the RGB parameter.

Sometimes it is also written ARGB (like RGBA, but the first data is alpha), which is the terminology used by Macromedia products. For example, 0x80FFFF00 is 50% transparent yellow because all parameters are represented in the range 0 to 255. 0x80 is 128, which is about half of 255.

PNG is an image format that uses RGBA.

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