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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The .ico file extension is a file format that is used by Microsoft Windows to display an image to represent computer icons, such as programs, shortcuts, Start Menu items or directories. To associate an image with a file in Microsoft Windows a .ico file must be used. An example of an icon is the small computer image associated with 'My Computer' or the Notepad icon that is associated with the Notepad.exe application within Microsoft Windows.
The .ico file type was introduced by the first edition of Windows and has slowly evolved in terms of maximum pixel size and the level of colour support. Windows 7 currently supports icon sizes up to 256 x 256 pixels at 32 bit (comprising 24 bit colour, and 8 bit transparency). However to ensure backwards compatibility with previous versions of Windows 8 bit versions are recommended.
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