Raster and Vector Graphic

The graphic can be of two types – raster and vector. It is due to the usage of two completely different approaches to creating, displaying and storing the image.

While choosing between raster and vector format it is necessary to define the targets of work with images. If photo quality of reproduction is required, then the raster image will be chosen. Vector format is preferable for displaying and processing logos, schemes, animations.

All the on-line images are provided in one of raster formats, recognised by browsers – GIF, JPG, PNG. Animation and visual effects for web-sites are mainly devloped in vector format – SWF.
 

Raster Graphic.

In reality any photo or image is a set of some continual elements. Areas of certain colours and shades of grey on a traditional not digital photo are also continual – the gradation can be smooth or steep, but areas of the same colour are always the areas of the same colour.

Computer graphic is based on different principles. There is nothing continual and the image, displayed on the screen or printed out, received from the skanner or digital camera, always consists of separate points. These points can be too small to be viewed with unadjusted eye, but nevertheless, a digital image is a mosaic or, in other words, raster.

Raster graphic is a principle of storing and processing a certain image in the form of matrix of points. Adobe PhotoShop is one of the best tools to deal with raster graphic. Photos as well as fullcolour complex graphic are stored in the form of raster images. The principles of working with such graphic agree with the approach to processing photos.
 

Rixel.

A raster image consists of a set of points, which line by line are used to form a final image. Both the location and colour of every point is preserved. The final mosaic forms an image which is perceived by our eyes. The pixel is a singe point which makes a raster image.

The number of pixels, which fit one inch, is called resolution and determines the quality of the picture. The higher is the resolution, the better image quality.

Apart from dpi, the resolution can be measured in pixels (a point on a monitor screen). For example, the monitor resolution of a computer can make 1024 by 768 pixels. It means that every line of points on the sreen contains 1024 points and 768 stands for the number of lines. Meanwhile, the screen resolution (points in one inch) is about 72.

Raster method of storing the image has many advantages. It is more natural not only for monitors but for scanners and printers as well. Raster method enables to use mathematic approaches to the image, as the photo image is a matrix of numbers to which you can employ any function. Only this method provides the opportunity to store and process full-colour image.

Though the method of raster image has some disadvantages as well. One of them is the volume of the stored information. The larger the raster image is, the larger number of bits it takes. The second drawback of the raster image is that the change of a line segment length, saved in the raster format, can appear to be a real challenge in practice as the segment length for the raster format is simply a certain colour of some set of points.

To turn the disadvantages of the raster image into advantages, it is obligatory to work with the vector image, for example, to consider the said line segment not as a set of points but as a vector.
 

Vector Graphic.

The vector is defined by two pairs of numbers—coordinates of a starting point and the direction or coordinates of starting and final points, plus information about the colour, and for all the points as that, not for a separate one. The vector method provides the opportunity to decrease the vector image several times in volume to compare with the raster one. Moreover, in the given example it is very easy to change the segment length from the point of view of programming – you should simply change the coordinates of one of its final points. On the same principle you can store circles and other geometric figures which make an image.

Working with the vector image – is the prerogative of such programmes as Corel Draw, Adobe Illustrator and Adobe Flash.

A raster image can be transformed into a vector format. The result of the transformation can be quite successful on condition that the image according to its content is line-art. The result of transforming a photo image can be rough but quite acceptable and for some tasks the only possible variant of working with the image.

One can also do the opposite – rasterize the vector graphic, export from the vector into one of the formats of raster graphic. Simultaneous usage of an imported raster image with the vector graphic is also possible.