|
Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygons—all of which are based on mathematical expressions—to represent images in computer graphics. Vector graphics are based on vectors (also called paths), which lead through locations called control points or nodes. Each of these points has a definite position on the x and y axes of the work plane and determines the direction of the path; further, each path may be assigned a stroke color, shape, thickness, and fill. These properties don't increase the size of vector graphics files in a substantial manner, as all information resides in the document's structure, which describes solely how the vector should be drawn. Vector graphics can be magnified infinitely without loss of quality, while pixel-based graphics cannot. The term ''vector graphics'' is typically used only for 2D (planar) graphics objects, in order to distinguish them from 2D raster graphics, which are also very common. 3D graphics as commonly implemented today (e.g., in OpenGL) are typically described using primitives like 3D points and polygons connecting these (which in turn describe surfaces); these 3D primitives are much more similar to vector graphics than to raster graphics, but aren't explicitly called ''vector graphics''. The equivalent of raster graphics in the 3D world are voxel-based graphics. == Overview == One 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 specialised systems. Vector graphics were also used on the TX-2 at the MIT Lincoln Laboratory by computer graphics pioneer Ivan Sutherland to run his program Sketchpad in 1963. Subsequent vector graphics systems, most of which iterated through dynamically modifiable stored lists of drawing instructions, include the IBM 2250, Imlac PDS-1, and DEC GT40. There was a home gaming system that used vector graphics called Vectrex as well as various arcade games like ''Asteroids'', ''Space Wars'' and many cinematronics titles such as "rip off", and "tail gunner" using vector monitors. Storage scope displays, such as the Tektronix 4014, could display vector images but not modify them without first erasing the display. In computer typography, modern outline fonts describe printable characters (glyphs) by cubic or quadratic mathematical curves with control points. Nevertheless, bitmap fonts are still in use. Converting outlines requires filling them in; converting to bitmaps is not trivial, because bitmaps often don't have sufficient resolution to avoid "stairstepping" ("aliasing"), especially with smaller visible character sizes. Processing outline character data in sophisticated fashion to create satisfactory bitmaps for rendering is called "hinting". Although the term implies suggestion, the process is deterministic, and done by executable code, essentially a special-purpose computer language. While automatic hinting is possible, results can be inferior to that done by experts. Modern vector graphics displays can sometimes be found at laser light shows, where two fast-moving X-Y mirrors position the beam to rapidly draw shapes and text as straight and curved strokes on a screen. Vector graphics can be created in form using a pen plotter, a special type of printer that uses a series of ballpoint and felt-tip pens on a servo-driven mount that moves horizontally across the paper, with the plotter moving the paper back and forth through its paper path for vertical movement. Although a typical plot might easily require a few thousand paper motions, back and forth, the paper doesn't slip. In a tiny roll-fed plotter made by Alps in Japan, teeth on thin sprockets indented the paper near its edges on the first pass, and maintained registration on subsequent passes. Some Hewlett-Packard pen plotters had two-axis pen carriers and stationery paper (plot size was limited). However, the moving-paper H-P plotters had grit wheels (akin to machine-shop grinding wheels) which, on the first pass, indented the paper surface, and collectively maintained registration. Present-day vector graphic files such as engineering drawings are typically printed as bitmaps, after vector-to-raster conversion. 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 3D rendering. Virtually all modern 3D rendering is done using extensions of 2D vector graphics techniques. Plotters used in technical drawing still draw vectors directly to paper. === Standards === The World Wide Web Consortium (W3C) standard for vector graphics is Scalable Vector Graphics (SVG). The standard is complex and has been relatively slow to be established at least in part owing to commercial interests. Many web browsers now have some support for rendering SVG data but full implementations of the standard are still comparatively rare. In recent years, SVG has become a significant format that is completely independent of the resolution of the rendering device, typically a printer or display monitor. SVG files are essentially printable text that describes both straight and curved paths, as well as other attributes. Wikipedia prefers SVG for images such as simple maps, line illustrations, coats of arms, and flags, which generally are not like photographs or other continuous-tone images. Rendering SVG requires conversion to raster format at a resolution appropriate for the current task. SVG is also a format for animated graphics. There is also a version of SVG for mobile phones. In particular, the specific format for mobile phones is called SVGT (SVG Tiny version). These images can count links and also exploit anti-aliasing. They can also be displayed as wallpaper. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「vector graphics」の詳細全文を読む スポンサード リンク
|