Vector images
Introduction
There is another type of file apart from bitmaps. These are known as 'vector images'. If you drew a circle in Paint or any other drawing application, rather than storing the information as a bitmap pixel by pixel, you store information about the geometric shapes that make up the picture. These are called the 'drawing objects'. You store the formula for a circle, its radius, its line thickness, where the circle should be drawn, colour information, and you do the same for straight lines, rectangles, curves and so on. If the vector image needs to be displayed, this information is taken by the drawing program and the drawing is reconstructed from the information given.
Coordinates and the user space
To draw a vector image, you need to have a 'user space', an area where all the shapes that make up an image can be drawn. positions in the user space area are defined by their coordinates. For example, you might need to draw a circle at position (10,5) in the user space:
If we created a face using a vector drawing program, the file would store the face as a 'drawing list'. A drawing list is simply the set of properties that defines the drawing. These properties allow the image to be reconstructed later in any program that supports that file type. For example, we might draw a face. When the file is saved, the drawing list showing the properties of our work of art might look like this:
draw circle
center 10, 5
radius 4
fill-color yellow
stroke-color black
stroke-width 1.00
draw circle
center 3, 3
radius 0.4
fill-color black
draw circle
center 6, 3
radius 0.4
fill-color black
draw line
start 0.3, 0.6
end 0.7, 0.6
stroke-color black
stroke-width 1.00
An application that opens this file might use the information in the file to draw this:
Rasterization
An application that needs to display this image takes the information in the file and then converts it into a bitmap. This process is called 'rasterization'. If you need to zoom in or out of the image (re-scale it), there is no loss of definition. If you zoomed into a bitmap image, eventually, you would see the pixels and the picture would become unrecognisable (a process called pixelisation). The image is simply redrawn using the formulas given.