Bitmap Images, also known as raster images, are made up of pixels in a grid. Each pixel is a pictures element; tiny dots of individual colour which when put together make up the image you se on screen. Computer monitors display the information through bitmap formats and usually show 70 to 100 pixels per square inch, but this depends on the resolution of the screen and its settings. A typical desktop background on your computer at home would be 32 by 32 pixels in size, in other words there are 32 dots of colour in a grid horizontally and 32 bits of colour vertically forming a square. When the dots combine they form the image we see. If you were to enlarge or magnify the icon then you would easily to see the individual dots of colour.
The resolution of the image controls its quality or how many dots there are per square inch, this is shown by a number and a unit, the unit is usually stated as DPI, dots per inch, or PPI, pixels per inch. Bitmap images will be displayed on your computer screen at approximately 100 ppi. However, when printing an image the printer needs much more image information than a monitor. In order to render the bitmap image accurately, a normal desktop printer will need any where from 150 ppi up to 300 ppi. Because bitmap images are dependant on their resolution, it is difficult to increase or decrease their size without loosing any image quality. When you downsize a bitmap image using a software’s resizing command the software has to discard pixels. Whereas when you increase the size of the image using the same command then the software has to create new pixels, the software then has to estimate the colour of the new pixel by looking at the colour values of the surrounding pixels, this process is called interpolation. Image formats which are bitmaps include BMP, GIF, JPEG OR JPG, PNG, PICT(MACINTOSH), PCX, TIFF AND PSD( Adobe Photoshop).
Vector images are the second main group of graphic images. They are made up of many different, individual objects. Each of those individual objects can be defined as ‘mathematical statements and has individual properties assigned to it such as colour, fill and outline’. [1] Vector images are resolution independent as they can be outputted to the highest quality at any scale.
Software used to create vector graphics are sometimes referred to as ‘object -based editing software’ [2]. Common vector formats include AI (Adobe Illustrator), CDR (CorelDRAW), CGM (computer Graphics Metafile), SWF (Shockwave Flash) and DXF (AutoCAD and other Cad software). Vector image files also tend to have much smaller file sizes than bitmap files. Currently all vector based images on the internet need browser plug-ins for them to be viewed.
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