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. The resultant 'lossy' file means that quality can never be recovered. The JPG format is often used in digital camera memory cards. 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.
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. JPEG is a joint standard of the International Telecommunications Union (ITU-T T.81) and the International Organization for Standardization (ISO 10918-1). JPEG involves a lossy compression mechanism using discrete cosine transform (DCT). Compression rates of 100:1 can be achieved, although the loss is noticeable at that level. Compression rates of 10:1 or 20:1 yield little degradation in image quality.
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Development of the TGA file format began in the mid eighties. A TGA file is most commonly associated with a TARGA image file (Truevision Advanced Raster Graphics Adapter). TGA files are bitmapped images, they were originally developed for use with Truevision's (now Pinnacle Systems) high-end graphics cards which were designed for video editing. TGA files are often seen in the video and animation industry, as well as by computer game manufacturers who use the TGA format to store texture files.
TGA files can store images with a range of bits, these include 8-bit, 16-bit, 24-bit or 32-bit which is 24-bit colour with transparency. They use a palette to define all available colours in an image. TGA images have typically large file sizes as every pixel is represented by a certain number of bits (dependant on the colour depth). However, they can be compressed using simple lossless run-length encoding, which can result in greatly reduced file sizes.