Alpha to coverage
is a
multisampling computer graphics
Computer graphics deals with generating images and art with the aid of computers. Computer graphics is a core technology in digital photography, film, video games, digital art, cell phone and computer displays, and many specialized applications. ...
technique, that replaces
alpha blending
In computer graphics, alpha compositing or alpha blending is the process of combining one image with a background to create the appearance of partial or full transparency. It is often useful to render picture elements (pixels) in separate pass ...
with a
coverage mask. This achieves
order-independent transparency
Order-independent transparency (OIT) is a class of techniques in rasterization, rasterisational computer graphics for rendering Transparency (graphic), transparency in a 3D scene, which do not require rendering geometry in sorted order for alpha co ...
for when
anti-aliasing Anti-aliasing may refer to any of a number of techniques to combat the problems of aliasing in a sampled signal such as a digital image or digital audio recording.
Specific topics in anti-aliasing include:
* Anti-aliasing filter, a filter used b ...
or semi-transparent
textures are used. This particular technique is useful for situations where dense foliage or grass must be rendered in a
video game
A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device) to generate visual fe ...
.
Alpha to coverage multisampling is based on regular
multisampling, except that the
alpha
Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...
coverage mask is
ANDed with the multisample mask. Alpha-to-coverage converts the
alpha
Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...
component output from the
pixel shader
In computer graphics, a shader is a computer program that calculates the appropriate levels of light, darkness, and color during the rendering of a 3D scene—a process known as '' shading''. Shaders have evolved to perform a variety of s ...
to a coverage mask. When the
multisampling is applied each output fragment gets a transparency of 0 or 1 depending on alpha coverage and the
multisampling result.
See also
*
Spatial anti-aliasing
In digital signal processing, spatial anti-aliasing is a technique for minimizing the distortion artifacts (aliasing) when representing a high-resolution image at a lower resolution. Anti-aliasing is used in digital photography, computer graphics ...
*
Multisample anti-aliasing
Multisample anti-aliasing (MSAA) is a type of spatial anti-aliasing, a technique used in computer graphics to remove jaggies.
It is an optimization of supersampling, where only the necessary parts are sampled more. Jaggies are only noticed in ...
*
Color depth
Color depth, also known as bit depth, is either the number of bits used to indicate the color of a single pixel, or the number of bits used for each color component of a single pixel. When referring to a pixel, the concept can be defined as bit ...
References
External links
GPU Gems 3 ‒ Chapter 4. Next-Generation SpeedTree RenderingStreet Fighter IV PC explained in detail
Image processing
Computer graphic artifacts
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