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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Developed in 1982 by Adobe Systems, the .ps extension is a file type used by the publishing industry. Prior to the development of PostScript, it was not possible to print images and text on the same page. Postscript addressed this by defining a language that allowed applications to instruct the printer how to display objects on the page. This file type revolutionised publishing allowing certain curved items to be printed that previously could only be printed on specialist CAD printers. Although no longer as popular or common as it was historically, it is still an important file type.
PostScript is actually a programming language as well as a file type. Typically files are created by applications such as Adobe Acrobat or Quark Xpress. Now a legacy file format, most printers and programs continue to support this format, with the only pre-requisite being a printer utility that supports PostScript. The file basically contains a set of instructions that tell the printer what to print and provide the co-ordinates on the page of where an object or text should be printed.