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→See also: added see also section for anti aliasing, as it is relevant for rasterisation
 
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{{Short description|Computer graphics manipulation technique}}{{refimprove|date=September 2018}}
{{Short description|Conversion of a vector-graphics image to a raster image}}{{refimprove|date=September 2018}}
[[File:Raster graphic fish 20x23squares sdtv-example.png|thumb|right|200px|raster graphic image]]
[[File:Raster graphic fish 20x23squares sdtv-example.png|thumb|right|200px|Raster graphic image]]
⚫
'''Rasterization''' (or '''rasterisation''') is the task of taking an image described in a [[vector graphics]] format (shapes) and converting it into a [[raster image]] (a series of [[pixel]]s, dots or lines, which, when displayed together, create the image which was represented via shapes).<ref name="Worboys1995">{{cite book|author=Michael F. Worboys|title=GIS: A Computer Science Perspective|url=https://books.google.com/books?id=duT2fcnQeJMC&pg=PA232|date=30 October 1995|publisher=CRC Press|isbn=978-0-7484-0065-2|pages=232–}}</ref><ref name="Chang2007">{{cite book|author=Kang-Tsung Chang|title=Programming ArcObjects with VBA: A Task-Oriented Approach, Second Edition|url=https://books.google.com/books?id=1DOY9xuxcosC&pg=PA91|date=27 August 2007|publisher=CRC Press|isbn=978-1-4200-0918-7|pages=91–}}</ref> The rasterized image may then be displayed on a [[computer display]], [[video display]] or [[computer printer|printer]], or stored in a [[bitmap]] file format. Rasterization may refer to the technique of drawing [[3D model (computer graphics)|3D model]]s, or the conversion of 2D [[rendering primitive]]s such as [[polygon]]s, [[line segment]]s into a rasterized format.


⚫
In [[computer graphics]], '''rasterisation''' ([[British English]]) or '''rasterization''' ([[American English]]) is the task of taking an [[Digital image|image]] described in a [[vector graphics]] format (shapes) and converting it into a [[raster image]] (a series of [[pixel]]s, dots or lines, which, when displayed together, create the image which was represented via shapes).<ref name="Worboys1995">{{cite book|author=Michael F. Worboys|title=GIS: A Computer Science Perspective|url=https://books.google.com/books?id=duT2fcnQeJMC&pg=PA232|date=30 October 1995|publisher=CRC Press|isbn=978-0-7484-0065-2|pages=232–}}</ref><ref name="Chang2007">{{cite book|author=Kang-Tsung Chang|title=Programming ArcObjects with VBA: A Task-Oriented Approach, Second Edition|url=https://books.google.com/books?id=1DOY9xuxcosC&pg=PA91|date=27 August 2007|publisher=CRC Press|isbn=978-1-4200-0918-7|pages=91–}}</ref> The rasterized image may then be displayed on a [[computer display]], [[video display]] or [[computer printer|printer]], or stored in a [[bitmap]] file format. Rasterization may refer to the technique of drawing [[3D model (computer graphics)|3D models]], or to the conversion of 2D [[rendering primitive]]s, such as [[polygon]]s and [[line segment]]s, into a rasterized format.
⚫
The term is derived from German ''Raster'' ('framework, schema'), from the [[Latin]] ''[[Rastrum|rāstrum]]'', "scraper, rake".<ref>{{OEtymD|raster}}</ref><ref>{{L&S|rastrum|ref}}</ref>


== 2D Images ==
== Etymology ==
⚫
The term "rasterisation" comes {{ety|de|Raster|grid, pattern, schema|la|[[Rastrum|rāstrum]]|scraper, rake}}.<ref>{{OEtymD|raster}}</ref><ref>{{L&S|rastrum|ref}}</ref>

== 2D images ==


=== Line primitives ===
=== Line primitives ===
{{Main|Line drawing algorithm}}
{{Main|Line drawing algorithm}}
[[Bresenham's line algorithm]] is an example of algorithm used to render a line.
[[Bresenham's line algorithm]] is an example of an algorithm used to rasterize lines.


=== Circle primitives ===
=== Circle primitives ===
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Rasterization is one of the typical techniques of rendering 3D models. Compared with other rendering techniques such as [[Ray tracing (graphics)|ray tracing]], rasterization is extremely fast and therefore used in most realtime 3D engines. However, rasterization is simply the process of computing the mapping from scene geometry to pixels and does not prescribe a particular way to compute the color of those pixels. The specific color of each pixel is assigned by a [[Pixel Shader|pixel shader]] (which in modern [[GPUs]] is completely [[Shading language|programmable]]). Shading may take into account physical effects such as light position, their approximations or purely artistic intent.
Rasterization is one of the typical techniques of rendering 3D models. Compared with other rendering techniques such as [[Ray tracing (graphics)|ray tracing]], rasterization is extremely fast and therefore used in most realtime 3D engines. However, rasterization is simply the process of computing the mapping from scene geometry to pixels and does not prescribe a particular way to compute the color of those pixels. The specific color of each pixel is assigned by a [[Pixel Shader|pixel shader]] (which in modern [[GPUs]] is completely [[Shading language|programmable]]). Shading may take into account physical effects such as light position, their approximations or purely artistic intent.


The process of rasterizing 3D models onto a 2D plane for display on a [[computer screen]] ("[[screen space]]") is often carried out by fixed function (non-programmable) hardware within the [[graphics pipeline]]. This is because there is no motivation for modifying the techniques for rasterization used at render time{{clarification needed|date=August 2016}} and a special-purpose system allows for high efficiency.
The process of rasterizing 3D models onto a 2D plane for display on a [[computer screen]] ("[[screen space]]") is often carried out by fixed function (non-programmable) hardware within the [[graphics pipeline]]. This is because there is no motivation for modifying the techniques for rasterization used at render time <ref>{{Cite web |title=Rasterization: a Practical Implementation |url=https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/overview-rasterization-algorithm.html |access-date=2023-10-06 |website=www.scratchapixel.com}}</ref> and a special-purpose system allows for high efficiency.


=== Triangle rasterization ===
=== Triangle rasterization ===
[[File:Top-left triangle rasterization rule.gif|thumb|right|rasterizing triangles using the top-left rule]]
[[File:Top-left triangle rasterization rule.gif|thumb|right|Rasterizing triangles using the top-left rule]]
A common representation of digital 3D models is [[Polygon mesh|polygonal]]. Before rasterization, individual polygons are broken down into triangles, therefore a typical problem to solve in 3D rasterization is rasterization of a triangle. Properties that are usually required from triangle rasterization algorithms are that rasterizing two adjacent triangles (i.e. those that share an edge)
[[Polygon mesh|Polygons]] are a common representation of digital 3D models. Before rasterization, individual polygons are typically broken down into triangles; therefore, a typical problem to solve in 3D rasterization is rasterization of a triangle. Properties that are usually required from triangle rasterization algorithms are that rasterizing two adjacent triangles (i.e. those that share an edge)


# leaves no holes (non-rasterized pixels) between the triangles, so that the rasterized area is completely filled (just as the surface of adjacent triangles). And
# leaves no holes (non-rasterized pixels) between the triangles, so that the rasterized area is completely filled (just as the surface of adjacent triangles). And
Line 36: Line 38:


== Quality ==
== Quality ==
[[File:Pixel vs subpixel precision.gif|thumb|right|Pixel (left) vs sub-pixel (right) precision]]
[[File:Line pixel subpixel aa.gif|thumb|right|Pixel precision (left) vs sub-pixel precision (middle) vs anti-aliasing (right)]]
The quality of rasterization can be improved by [[spatial anti-aliasing|anti-aliasing]], which creates "smooth" edges. [[sub-pixel resolution|Sub-pixel precision]] is a method which takes into account positions on a finer scale than the pixel grid and can produce different results even if the endpoints of a primitive fall into same pixel coordinates, producing smoother movement animations. Simple or older hardware, such as the [[PlayStation_(console)|original PlayStation]], lacked sub-pixel precision in 3D rasterization.<ref>{{cite web |title=PlayStation rasterization issues |url=https://www.libretro.com/index.php/mednafenbeetle-psx-pgxp-arrives/#more-45256 |website=Libretro |access-date=19 April 2020}}</ref>
The quality of rasterization can be improved by [[spatial anti-aliasing|antialiasing]], which creates "smooth" edges. [[sub-pixel resolution|Sub-pixel precision]] is a method which takes into account positions on a finer scale than the pixel grid and can produce different results even if the endpoints of a primitive fall into same pixel coordinates, producing smoother movement animations. Simple or older hardware, such as [[PlayStation 1]], lacked sub-pixel precision in 3D rasterization.<ref>{{cite web |title=PlayStation rasterization issues |url=https://www.libretro.com/index.php/mednafenbeetle-psx-pgxp-arrives/#more-45256 |website=Libretro |date=4 October 2016 |access-date=19 April 2020}}</ref>


==See also==
==See also==
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* [[Sub-pixel resolution]]
* [[Sub-pixel resolution]]
* [[Image tracing]]
* [[Image tracing]]
* [[Hidden surface determination]]
* [[Hidden-surface determination]]
* [[Bresenham's line algorithm]] for a typical method in rasterization
* [[Bresenham's line algorithm]] for a typical method in rasterization
* [[Scanline rendering]] for line-by-line rasterization
* [[Scanline rendering]] for line-by-line rasterization
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* [[Triangulated irregular network]], a vector source for topography data, often rasterized as a (raster) [[digital elevation model]].
* [[Triangulated irregular network]], a vector source for topography data, often rasterized as a (raster) [[digital elevation model]].
* [[Display list]]
* [[Display list]]
* [[Spatial anti-aliasing]]


== References ==
== References ==
{{reflist}}
{{reflist}}


==External links==
== External links ==
*[http://www.drdobbs.com/parallel/184404919 Michael Abrash’s articles on computer graphics]
*[http://www.drdobbs.com/parallel/184404919 Michael Abrash’s articles on computer graphics]
*[https://msdn.microsoft.com/en-us/library/windows/desktop/ff476882(v=vs.85).aspx Microsoft’s DirectX API]
*[https://msdn.microsoft.com/en-us/library/windows/desktop/ff476882(v=vs.85).aspx Microsoft’s DirectX API]
*[http://www.opengl.org OpenGL API]
*[http://www.opengl.org OpenGL API]
*[http://mathworld.wolfram.com/topics/MatrixTypes.html Matrices (including transformation matrices) from MathWorld]
*[http://mathworld.wolfram.com/topics/MatrixTypes.html Matrices (including transformation matrices) from MathWorld]
*[http://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation Rasterization, a Practical Implementation]
*[https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/rasterization-stage.html Rasterization, a Practical Implementation]


{{Graphics Processing Unit}}
{{Graphics Processing Unit}}

Latest revision as of 09:04, 23 May 2024

Raster graphic image

In computer graphics, rasterisation (British English) or rasterization (American English) is the task of taking an image described in a vector graphics format (shapes) and converting it into a raster image (a series of pixels, dots or lines, which, when displayed together, create the image which was represented via shapes).[1][2] The rasterized image may then be displayed on a computer display, video display or printer, or stored in a bitmap file format. Rasterization may refer to the technique of drawing 3D models, or to the conversion of 2D rendering primitives, such as polygons and line segments, into a rasterized format.

Etymology

[edit]

The term "rasterisation" comes from German Raster 'grid, pattern, schema' and Latin rāstrum 'scraper, rake'.[3][4]

2D images

[edit]

Line primitives

[edit]
Main article: Line drawing algorithm

Bresenham's line algorithm is an example of an algorithm used to rasterize lines.

Circle primitives

[edit]

Algorithms such as Midpoint circle algorithm are used to render circle onto a pixelated canvas.

3D images

[edit]

Rasterization is one of the typical techniques of rendering 3D models. Compared with other rendering techniques such as ray tracing, rasterization is extremely fast and therefore used in most realtime 3D engines. However, rasterization is simply the process of computing the mapping from scene geometry to pixels and does not prescribe a particular way to compute the color of those pixels. The specific color of each pixel is assigned by a pixel shader (which in modern GPUs is completely programmable). Shading may take into account physical effects such as light position, their approximations or purely artistic intent.

The process of rasterizing 3D models onto a 2D plane for display on a computer screen ("screen space") is often carried out by fixed function (non-programmable) hardware within the graphics pipeline. This is because there is no motivation for modifying the techniques for rasterization used at render time [5] and a special-purpose system allows for high efficiency.

Triangle rasterization

[edit]
Rasterizing triangles using the top-left rule

Polygons are a common representation of digital 3D models. Before rasterization, individual polygons are typically broken down into triangles; therefore, a typical problem to solve in 3D rasterization is rasterization of a triangle. Properties that are usually required from triangle rasterization algorithms are that rasterizing two adjacent triangles (i.e. those that share an edge)

  1. leaves no holes (non-rasterized pixels) between the triangles, so that the rasterized area is completely filled (just as the surface of adjacent triangles). And
  2. no pixel is rasterized more than once, i.e. the rasterized triangles don't overlap. This is to guarantee that the result doesn't depend on the order in which the triangles are rasterized. Overdrawing pixels can also mean wasting computing power on pixels that would be overwritten.

This leads to establishing rasterization rules to guarantee the above conditions. One set of such rules is called a top-left rule, which states that a pixel is rasterized if and only if

  1. its center lies completely inside the triangle. Or
  2. its center lies exactly on the triangle edge (or multiple edges in case of corners) that is (or, in case of corners, all are) either top or left edge.

A top edge is an edge that is exactly horizontal and lies above other edges, and a left edge is a non-horizontal edge that is on the left side of the triangle.

This rule is implemented e.g. by Direct3D[6] and many OpenGL implementations (even though the specification doesn't define it and only requires a consistent rule[7]).

Quality

[edit]
Pixel precision (left) vs sub-pixel precision (middle) vs anti-aliasing (right)

The quality of rasterization can be improved by antialiasing, which creates "smooth" edges. Sub-pixel precision is a method which takes into account positions on a finer scale than the pixel grid and can produce different results even if the endpoints of a primitive fall into same pixel coordinates, producing smoother movement animations. Simple or older hardware, such as PlayStation 1, lacked sub-pixel precision in 3D rasterization.[8]

See also

[edit]

References

[edit]
  1. ^ Michael F. Worboys (30 October 1995). GIS: A Computer Science Perspective. CRC Press. pp. 232–. ISBN 978-0-7484-0065-2.
  2. ^ Kang-Tsung Chang (27 August 2007). Programming ArcObjects with VBA: A Task-Oriented Approach, Second Edition. CRC Press. pp. 91–. ISBN 978-1-4200-0918-7.
  3. ^ Harper, Douglas. "raster". Online Etymology Dictionary.
  4. ^ rastrum. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  5. ^ "Rasterization: a Practical Implementation". www.scratchapixel.com. Retrieved 2023-10-06.
  6. ^ "Rasterization Rules (Direct3D 9)". Microsoft Docs. Retrieved 19 April 2020.
  7. ^ OpenGL 4.6 (PDF). p. 478.
  8. ^ "PlayStation rasterization issues". Libretro. 4 October 2016. Retrieved 19 April 2020.
[edit]
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