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Computing Science
CMPT 165
Colin Stewart

ImagesDigital Storage The smallest unit of storage on a computer is called a bit A bit can store one of two possible values0 or 1 Bits cant store very much data A larger unit of storage is a byte A byte consists of 8 bits and can store one of 256 28 possible numbers0 to 255 A colour consists of three colour components red green and blue and each colour component has one of 256 possible intensity levels As such each colour component requires one byte of storage One full colour requires 3 bytes of storage24 bits in total This kind of colour is often called 24bit colour There are larger units of storage than bytes A kilobyte KB consists of 1024 210 bytes A megabyte MB consists of 1024 kilobytes A gigabyte GB consists of 1024 megabytes A terabyte TB consists of 1024 gigabytes A petabyte PB consists of 1024 terabytes Many digital images consist of a grid of pixels tiny squares Each pixel has one colour Images that consist of a grid of pixels are called bitmap images One of the basic image file formats for storing bitmap images is the BMP file format BMP has a bmp file extension BMPs are the easiest way to store bitmap images however they have a very large file size Each pixel in a 24bit colour bitmaps required 3 bytes of storage Thus a standard TV imagewidth 640 height 480would require 640 x 480 x 3921600 bytes900 kilobytes A highdefinition TV imagewidth 1920 height 1080would require 1920 x 1080 x 36220800 bytes593 megabytes An image from a 10megapixel camerawidth 3648 height 2736would require 3648 x 2736 x 329942784 bytes2856 megabytes In short BMP files are enormous but why is a high file size a problem Two reasons Storage capacity Transfer time The most obvious problem with a high file size is that storage space is limited Hard drives and optical disks DVD Bluray etc are big but not infinite If we can reduce file sizes we can store more files As storage capacity continues to increase this will become less and less of an issue A bigger problem with high file sizes is transfer timethat is how much time it takes to send a file particularly over the Internet With current technology a 900 KB image will take a few seconds to loadit wont be instant If we reduce file sizes we can reduce the amount of time spent waiting for files to transfer So how can we reduce the file size of an image
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