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vector images and bitmap images

There are two main categories of images:

• bitmap images (also called raster images): these are pixeled images, i.e. a set of points (pixels) contained in a table, each of these points having one or more values describing its colour.
• vector images: vector images are representations of geometrical entities such as circles, rectangles or segments. These are represented by mathematical formulae (a rectangle is defined by two points, a circle by a centre and a radius, a curve by several points and an equation). The processor will “translate” these forms into information that a can be interpreted by the graphics card.

Since a vector image is only made up of mathematical entities, it is possible to easily apply geometrical transformations to it (zoom, stretching�), while a bitmap image, made up of pixels, will not be able to undergo such transformations without suffering a loss of information called distortion. The appearance of pixels in an image following a geometrical transformation (in particular when enlarging it) is called pixellation (also know as aliasing). Moreover, vector images (called clipart in the case of a vector object) make it possible to define an image with very little information, which makes the files quite small.

On the other hand, a vector image only allows simple forms to be represented. Although it is true that a superposition of various simple elements can yield very impressive results, it isn’t possible to describe all images by vectors; this is particularly the case of realistic photographs.

Vector image	Bitmap image

The “vector” image above is just a representation of what a vector image could resemble, because the quality of the image depends on the device used to make it visible to the eye. Your screen probably allows you to see this image with a resolution of at least 72 pixels per inch; the same file printed on a printer would offer a better image quality because it would be printed using at least 300 pixels per inch.

Thanks to the technology developed by Macromedia and its software Macromedia Flash, or the SVG plug-in the vector format can be used on the Internet today.

Dernière modification le Thursday October 16, 2008 02:43:16 PM.