Raster And Vector Graphics In Computer Graphics


Raster And Vector Graphics In Computer Graphics

In computer graphics, graphic image types are generally broken down into two basic categories:

1)      Raster Graphics: A raster graphic is made up of a large number of very small colored dots, similar to a television screen or a monitor. This is the most common computer graphics format, especially on the World Wide Web.

Raster graphics are good for photographs, for images that will only be displayed on a computer screen, and for images in which print quality is not of paramount concern. The majority of “paint” programs generate raster graphics. Also, scanners generate raster images. Computer raster graphic image file formats include TIF, BMP, and JPG.

Raster images have a variable resolution, meaning that one can specify how many dots of image information anyone wants to pack into each inch. The more dots per inch (dpi), the finer the image detail or resolution, but also the higher the memory requirements. Monitor screen resolution is 72 dpi (Mac) and 96 dpi (Windows).

Types of Raster Graphics

i)                    Uncompressed Raster Files: Such as Windows bitmaps (.bmp) or X- windows pixmaps (.xpm) are very large, but they display very quickly, with little computation. This makes them good for such things as backgrounds.

ii)                  Compressed Raster Files: In a bitmap, a great many pixels are probably of the same color: Instead of listing the definition of that color 4000 times inside the image file, the computer can call that color “2”, list its definition once at the beginning of the file, and thereafter refer to it as “2”. This is the basic idea behind graphics file compression.

By using this simple technique file size can be greatly reduced, and only minimal computation is required to display the file.

2)      Vector Graphics: Vector graphics formats are complementary to raster graphics, which is the representation of images as an array of pixels, as it is typically used for the representation of photographic images.

Vector formats are different in that they store images as a group of mathematically defined curves and shapes. Vector formats retain their quality when they are rotated, resized, and printed. Vector graphics are the correct format for images with sharp lines and text, and with a low number of colors, for example, engineering or mathematical diagrams, charts and graphs.

The other good thing about vector graphics is that they are more editable than raster graphics. In raster graphics programs drawing a line or a circle is in reality just setting a bunch of pixels. In vector graphics, one is actually drawing a line, and after drawing it one can pick it up, resize it, stretch it, change its color, and a great many other things not possible in raster graphics