|
In computer graphics, image tracing, raster-to-vector conversion or vectorization is the conversion of raster graphics into vector graphics. ==Background== An image does not have any structure: it is just a collection of marks on paper, grains in film, or pixels in a bitmap. While such an image is useful, it has some limits. If the image is magnified enough, its artifacts appear. The halftone dots, film grains and pixels become apparent. Images of sharp edges become fuzzy or jagged. See, for example, pixelation. Ideally, a vector image does not have the same problem. Edges are represented as a mathematical lines or curves, and they can be magnified thousands of times — until the precision of the numbers becomes an issue. The task in vectorization is to convert a two-dimensional image into a two-dimensional vector representation of the image. It is not examining the image and attempting to recognize or extract a three-dimensional model; it is not a vision system. For most applications, vectorization does not involve optical character recognition; characters are treated as lines, curves, or filled objects without attaching any significance to them. An advantage is that the shape of the character is preserved, so artistic embellishments remain. Continuous tone photographs (such as live portraits) are not good candidates for vectorization. Synthetic images such as maps, cartoons, logos, clip art, and technical drawings are candidates for vectorization. Those images could have been originally made as vector images because they are based on geometric shapes or drawn with simple curves. The input is an image, but that image may be in many forms such as a photograph, a drawing on paper, or one of several raster file formats. Programs that do raster-to-vector conversion may accept bitmap formats such as TIFF, BMP and PNG. The output is a vector file format. Common vector formats are SVG, DXF, EPS, EMF and AI. Vectorization is used to update images or recover work. Personal computers often come with a simple paint program that produces a bitmap output file. These programs allow users to make simple illustrations by adding text, drawing outlines, and filling outline with a specific color. Only the results of these operations (the pixels) are saved in the resulting bitmap; the drawing and filling operations are discarded. Vectorization can be used to recapture some of the information that was lost. Vectorization is also used to recover information that was originally in a vector format but has been lost or has become unavailable. A company may have commissioned a logo from a graphic arts firm. Although the graphics firm used a vector format, the client company may not have a copy of that format. Later, the company may get a vector format by scanning and vectorizing a paper copy of the logo. 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「Image tracing」の詳細全文を読む スポンサード リンク
|