JPEG involves a lossy compression mechanism using discrete cosine transform (DCT). JPEG is a joint standard of the International Telecommunications Union (ITU-T T.81) and the International Organization for Standardization (ISO 10918-1). JPG is a graphical file format for editing still images, it offers a symmetrical compression technique which is processor intensive and time consiming in both compression and decompression. The JPG file is a great format as it often manages to compress files to 1/10 of the size of the original file which is especially good for saving on bandwidth. The JPG format is often used in digital camera memory cards. The resultant 'lossy' file means that quality can never be recovered. JPG's are often used for web sites and email as they are generally smaller file sizes as they are lossy meaning that some image quality is lost when the JPG is compressed and saved.
Images with fewer colors will compress more efficiently under LZW compression. 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). 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. 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 GIF file format was invented by Compuserve for their online service, but they made the specifications publicly available. It uses the lossless data compression technique which reduces the file size without any impact on the quality. 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. 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. The GIF file format is a type of bitmap image and has become popular due to the growth of the internet.
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