Vector graphics
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Example showing effect of vector graphics on scale: (a) original vector-based illustration; (b) illustration magnified 8x as a vector image; (c) illustration magnified 8x as a raster image. Raster images scale poorly, but vector-based images can be scaled indefinitely without degradation. (Images were converted to JPEG for display on this page.) |
Vector graphics or
geometric modeling is the use of geometrical
primitives such as
points,
lines,
curves, and
polygons, which are all based upon mathematical equations to represent
images in
computer graphics. It is used by contrast to the term
raster graphics, which is the representation of images as a collection of
pixels (dots).The human eye works as a bitmap picture: it catches the image in a mosaic raster of photon recipient nerves, a pixel image. But the brain â€" according to recent studies â€" handles it as a vector image. Perhaps because â€" like in
computers â€" this is easier to store. It explains why humans can recognize simple drawings like cartoons with just outlines because this is so close to what the human brain makes of the visual world anyway. It also serves as an explanation for the fact that logos and signs with easy and geometric shapes are more easily remembered and recognized.
All modern current computer video displays translate vector representations of an image to a
raster format. The raster image, containing a value for every pixel on the screen, is stored in memory and the entire screen is repainted 30 or more times per second.
Starting in the earliest days of
computing in the
1950s and into the
1980s, a different type of display, the
vector graphics system, was used. In these systems the electron beam of the
CRT display monitor was steered directly to trace out the shapes required, line segment by line segment, with the rest of the screen remaining black. This process was repeated many times a second to achieve a flicker-free or near flicker-free picture. These systems allowed very high-resolution
line art and moving images to be displayed without the (for that time) unthinkably huge amounts of memory that an equivalent-resolution raster system would have needed. These vector-based monitors were also known as
X-Y displays.
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Vectorising is good for removing unnecessary detail from a photograph. (Images were converted to JPEG for display on this page.) |
Two of the first uses of vector graphic displays was the US
SAGE air defense system. Vector graphics systems were only retired from U.S. en route
air traffic control in
1999 and are likely still in use in military and specialized systems. Vector graphics were also used on the
TX-2 at the
MIT Lincoln Laboratory by computer graphics pioneer
Ivan Sutherland to run his revolutionary program
Sketchpad in 1963.
Subsequent vector graphics systems include Digital's GT40 [
1]. There was a home gaming system that used vector graphics called
Vectrex [
2] as well as various arcade games like
Asteroids and
Space Wars. The
Tektronix 4014 also deserves a mention even though the display was static.
The term
vector graphics is mainly used today in the context of two-dimensional computer graphics. It is one of several modes an artist can use to create an image on a raster display. Other modes include text,
multimedia and 3-d
rendering. Virtually all modern 3-d rendering is done using extensions of 2-d vector graphics techniques.
Plotters used in
technical drawing still draw vectors directly to
paper.
For example, consider a
circle of
radius r. The main pieces of
information a
program needs in order to draw this circle are
# the radius
r# the
location of the center point of the circle# stroke line style and colour (possibly transparent)# fill style and colour (possibly transparent)
Advantages to this style of
drawing over
raster graphics:
*This minimal amount of information translates to a much smaller
file size compared to large raster images (the
size of representation doesn't depend on the
dimensions of the object).
*Correspondingly, one can indefinitely zoom in on e.g. a circle arc, and it remains smooth. On the other hand, a polygon representing a curve will reveal being not really curved.
*On zooming in, lines and curves need not get wider proportionally. Often the width is either not increased or less than proportional. On the other hand, irregular curves represented by simple geometric shapes may be made proportionally wider when zooming in, to keep them looking smooth and not like these geometric shapes.
*The parameters of objects are stored and can be later modified. This means that
moving,
scaling,
rotating,
filling etc. doesn't degrade the
quality of a drawing. Moreover, it is usual to specify the dimensions in
device-independent units, which results in the best possible
rasterization on raster
devices.
*From a 3-D perspective, rendering shadows is also much more realistic with vector graphics, as shadows can be abstracted into the rays of light which form them. This allows for photo realistic images and renderings.
* lines and
polylines
*
polygons
*
circles and
ellipses
*
BĂ©zier curves
*
Bezigons
*
Text (in computer fonts such as
TrueType where each letter is created from
BĂ©zier curves)
This list is not complete. There are various types of curves (
Catmull-Rom splines,
NURBS etc.), which are useful in certain applications.
Often, a
bitmap image is considered as a primitive object. From the conceptual view, it behaves as a
rectangle.
Vector graphics editors typically allow to rotate, move, mirror, stretch, skew, generally perform
affine transformations of objects, change
z-order and combine the primitives into more complex objects.
More sophisticated
transformations include set
operations on closed
shapes (
union,
difference,
intersection, etc.)
Vector graphics are ideal for simple or composite drawings that need to be device-independent, or do not need to achieve
photo-realism. For example, the
PostScript and
PDF page description languages use a vector graphics model.
In
3D computer graphics, vectorized surface representations are most common (bitmaps can be used for special purposes such as surface texturing, height-field data and
bump mapping). At the low-end, simple
meshes of
polygons are used to represent geometric detail in applications where interactive
frame rates or
simplicity are important. At the high-end, where one is willing to trade-off higher rendering times for increased image
quality and
precision, smooth
surface representations such as
BĂ©zier patches,
NURBS or
Subdivision surfaces are used. One can however achieve a smooth surface rendering from a polygonal mesh through the use of shading algorithms such as
Phong.
*
Computer-aided design*
Electronic maps*
Graphics file format*
Graphics program*
GXL*
List of vector graphics editors*
List of vector graphics markup languages*
Raster to vector*
SVG*
Shapefile*
Vector game*
Vector graphics editor*
Vexel*
Web graphics*
Wikipedia:Graphics tutorials*
WMF*
OpenVG A royalty-free, cross-platform API for hardware accelerated two-dimensional vector and raster graphics.
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AmanithVG an OpenVG implementation over OpenGL and OpenGL|ES
*
Amanith open vector graphics framework
*
Cairo open vector graphics library
*
Inkscape An open source vector graphics editor.
*http://www.vectorportal.com/ free vector graphics
*http://www.planiglobe.com/ free vector graphic maps
*http://www.Vectorpeeps.com/ Vector art community
*http://www.scoshi.co.uk/vector.htm A selection of vector art
*
Digital Vector Maps Royalty-free vector maps in Illustrator and editable PDF formats
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Graphics Factory Royalty-free vector clip art downloads by subscription.
