BMP is a standard image file format which was historically used by computers running the Windows operating system. The format is more commonly know as Bitmap files. The term bitmap was originally coined in computer programming to refer to a map of bits. Historically when you saved an image on your home PC you might have saved it as a .bhp file, this is becoming less common with .jpeg the preferred image file format with the advent of digital cameras.
Bitmap files are housed in a device-independent bitmap (DIB) format. The term device independent means that the bitmap specifies pixel color in a form independent of the method used by a display to represent color. This enables Windows to show the bitmap on any type of display device - such as your monitor.
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The GIF file format is a type of bitmap image and has become popular due to the growth of the internet. This file format supports up to 8 bits per pixel therefore giving an image the ability to contain 256 distinct colours chosen from the 24-bit RGB colour space. It also supports animations and whenever you see a logo or other sharp edged line art then you are probably dealing with the GIF format. It uses the lossless data compression technique which reduces the file size without any impact on the quality.
The GIF file format was invented by Compuserve for their online service, but they made the specifications publicly available. GIFs are able to hold multiple bitmaps of up to 256 colors each, using LZW (Lempel Zev Welch - a simple form of file compression that removes inefficiencies in the data storage without losing data or distorting the image) compressed raster data to minimize file sizes. The idea is to lessen the amount of colours in a GIF image to the minimum number necessary and to therefore remove stray colors that are not required to represent the image. A GIF graphic is unable to have more than 256 colors but it can have fewer colors, down to the minimum of two (black and white). Images with fewer colors will compress more efficiently under LZW compression.
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