What makes a vector graphic scalable and a normal image not?

Question

I am not sure if this is the right location to ask this, but I am really wondering, what makes the difference between a vector graphic and a normal image? Why are they not both scalable without making the pixels clearly visible? Does a graphics card need to perform a lot of arithmetic calculations for this on a vector? And why doesn't it work like that on a normal image? I have the following image to describe the difference.

Answer 1

A raster image is an array of tiny squares with a given uniform color. The pixels forming a regular grid, only the colors are given, coordinates are implicit.

A vector image is a set of more complex shapes such as polygons, circles and Bezier curves, filled with a solid color (sometimes gradients or textures). The shapes are described by a number of parameters and/or control points.

You understand that the raster representation is only an approximation of the desired circle, using intermediate shades of gray to lessen the staircase effect on the outline. The vector representation truly describes a circle.

In both cases, the graphics card needs to render the images. Processing of the raster is much easier due to the simple nature of the squares.

In the zoomed-in views, notice that the outline of the circle on the left are neat; but the outlines of the pixels on the right are neat too (you see nice squares) !

Also note that in both cases the graphics card convertes the images to a raster having the resolution of the screen (the screen IS a raster image of fixed resolution).

Answer 2

The main differences between Vector and raster is how the image is stored.

At its simplest raster graphics are stored as the location and color of the pixels so when you zoom in this it what you see. in order to get the 'smooth' look they use anti-aliasing (blurring the pixels)

Vector graphics are stored as points and vectors (lines between the points) so the computer can render the image using by working out what lines go the what points and how it will look.

for a more detailed look take a look at the wiki pages:

http://en.wikipedia.org/wiki/Vector_graphics

http://en.wikipedia.org/wiki/Raster_graphics