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RGBA color space
 
 
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RGBA stands for Red Green Blue Alpha. While it is sometimes described as a color space, it is actually simply a use of the RGB color model, with extra information. The color is RGB, and may belong to any RGB color space, but an integral alpha value as invented by Catmull
Edwin Catmull

Edwin Catmull, Ph.D. is an Academy Award winning computer scientist and current president of Walt Disney Animation Studios and Pixar Animation Studios....
 and Smith
Alvy Ray Smith

Alvy Ray Smith III is an American engineer and noted pioneer in computer graphics....
 between 1971 and 1972 enables alpha blending
Alpha compositing

In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial transparency....
 and alpha compositing
Alpha compositing

In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial transparency....
. The inventors named alpha after the Greek letter in the classic linear interpolation
Linear interpolation

Linear interpolation is a method of curve fitting using linear polynomials. It is heavily employed in mathematics , and numerous applications including computer graphics....
 formula aA + (1-a)B.

The alpha channel is normally used as an opacity channel.






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RGBA stands for Red Green Blue Alpha. While it is sometimes described as a color space, it is actually simply a use of the RGB color model, with extra information. The color is RGB, and may belong to any RGB color space, but an integral alpha value as invented by Catmull
Edwin Catmull

Edwin Catmull, Ph.D. is an Academy Award winning computer scientist and current president of Walt Disney Animation Studios and Pixar Animation Studios....
 and Smith
Alvy Ray Smith

Alvy Ray Smith III is an American engineer and noted pioneer in computer graphics....
 between 1971 and 1972 enables alpha blending
Alpha compositing

In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial transparency....
 and alpha compositing
Alpha compositing

In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial transparency....
. The inventors named alpha after the Greek letter in the classic linear interpolation
Linear interpolation

Linear interpolation is a method of curve fitting using linear polynomials. It is heavily employed in mathematics , and numerous applications including computer graphics....
 formula aA + (1-a)B.

The alpha channel is normally used as an opacity channel. If a pixel has a value of 0% in its alpha channel, it is fully transparent
Transparency (graphic)

Transparency is possible in a number of graphics file formats. The term transparency is used in various ways by different people, but at its simplest there is "full transparency" i.e....
 (and, thus, invisible), whereas a value of 100% in the alpha channel gives a fully opaque pixel (traditional digital images). Values between 0% and 100% make it possible for pixels to show through a background like a glass (translucency), an effect not possible with simple binary (transparent or opaque) transparency. It allows easy image compositing
Digital compositing

Digital compositing is the process of digitally assembling multiple images to make a final image, typically for print, film or screen display. It is the evolution into the digital realm of optical film compositing....
. Alpha channel values can be expressed as a percentage, integer, or real number between 0 and 1 like RGB parameters.

Sometimes this is referred as ARGB (like RGBA, but first datum is alpha), which is used, for example, in Macromedia
Macromedia

Macromedia was a United States graphics and Web development software house headquartered in San Francisco, California producing such products as Adobe Flash....
 products terminology. For example, 0x80FFFF00 is 50%-transparent yellow, because all parameters are expressed on a 0-to-255 scale. 0x80 is 128, approximately half 255 (alpha 50%); 0xFF is 255, the greatest value a parameter can have (pure red); the second 0xFF is like the previous, but for green; and 0x00 is 0 in decimal (no blue). Red, green, and half transparency mixture are 50% transparent yellow.

PNG is an image format that uses RGBA.

See also

  • Alpha compositing
    Alpha compositing

    In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial transparency....
  • Digital compositing
    Digital compositing

    Digital compositing is the process of digitally assembling multiple images to make a final image, typically for print, film or screen display. It is the evolution into the digital realm of optical film compositing....
  • RGB (Red Green Blue, with no transparency effects)
  • scRGB color space
    ScRGB color space

    scRGB is a wide color gamut RGB color spaces created by Microsoft that uses the same color primaries and white/black points as the sRGB color space but uses 16-bit floating point linear values per component instead of gamma correction 8-bit integers....
    , a high definition color space
    Color space

    A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components ....
     with alpha channel


External links

  • on W3C PNG specification
  • Preview page with implementation info on CSS3.info