|Vector images are images made up of lines described mathematically|
|Raster images are grids of dots, or pixels, each pixel containing colour information. They are also known as bitmaps|
This vector image shows a line from x1,y1 to x2,y2
If this image were sent to a pen plotter, the image would translate as instructions to the plotter to lift the pen off the paper, move to coordinate x1,y1, lower the pen onto the paper and move to x2,y2, so drawing the line.
In this way, straight lines, arcs and circles can be drawn and the lines are perfect.
In the raster image below, the area is divided into a number of pixels and the impression of a line is given by some pixels being black and others white.
Raster image 8*6 pixels
PIXEL = PIcture ELement
With so few pixels, the line is very steppy.
Raster image 16*12 pixels
With more pixels, the line is less jagged, but the filesize is bigger.
File size is proportional to number of pixels
As in the example above,
8 * 6 = 48 pixels
16 * 12 = 192 pixels
Or a more realistic sized image ....
640 * 480 = 307,200 pixels
1280 * 960 = 1,228,800 pixels
If you multiply the width and height by 2, the filesize increases by a factor of 4.
So, if you scale your image by 50 percent, you are halving the width and height, but you are reducing the filesize by a factor of 4.