Images are a media type displayed as visual information. They can be drawings, paintings or photographs. Images are used to create interest and provide information. Photographs and other types of graphical data are designed specifically for display. An image on a screen is made up of dots called pixels. A pixel is the smallest part of the screen that can be controlled by the computer or other device. The total number of pixels on a screen is called its resolution. (ie New iPad has Retina display, 2048 x 1536 resolution). An image can be represented in two different ways. Either a Bitmap or a Vector. Typical file formats for a bitmap can be JPEG, GIF, PNG and BMP. Vector images can be SVG, WMF and EMF.
Bitmap
Bitmap images treat each dot in an image separately. These dots or pixels can be different colours with each colour being represented as a binary number. Bitmaps produce good quality images where shading and detail are needed.
To calculate the uncompressed storage needed for a bitmap you will need to calculate the total number of pixels and multiply by the colour or bit depth. For example, if an image is 1200 by 800 pixels, the total number of pixels will be 960,000. If the bit depth is 24 then each pixel needs 3 bytes of storage therefore the total file size will be 960,000 X 3 =2,880,000. The size of this image in kilobytes will be 2,880,000 divided by 1024 = 2812.5 kB. Divide this by 1024 to convert to megabytes. The image would require 2.74MB of storage.
Bitmap images are often compressed to reduce their file size for storage. Some of these compression formats will not alter the image quality. This is called lossless compression however others will remove some parts of the image. This is known as lossy compression.
Vector
Vector images or graphics are made up of objects such as straight lines, curves or shapes. Each portion of the image is represented mathematically. Each object is defined by its characteristics such as positions, width of the lines and patterns. The total size of the data required to represent a vector image is usually less than that of an equivalent Bitmap image. Vector images can be resized to any required resolution without loosing clarity. They are generally unsuitable for photographic images.
Common vector graphics include Scalable Vector Graphics (SVG), Windows Metafile (WMF) and Enhanced Metafile (EMF).
View the video below to get an overview of the differences between a Vector and Bitmap image.