Telecom Dictionary - Definitions of terms

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Tagged Image File Format Definition

Tagged Image File Format (abbreviated TIFF) - A file format used to store an image using the particular data structure of the file. Tagged Image File Format is a raster file format for digital images, which was developed by Aldus and Microsoft for use with PostScript printing and is now controlled by Adobe.

TIFF has become the de facto standard graphics format for high color depth (32-bit) graphics, is widely used in image manipulation applications such as Photoshop, DTP, and scanning, and can be directly manipulated by PostScript. It can be used with black and white, gray scale, 8-bit color, and 24-bit color images, and transfers well between different platforms.TIFF images can be compressed using LZW compression or other compression formats. TIFF is commonly used in desktop publishing and serves as an interface to numerous scanners and graphics packages.

TIFF includes a number of options that can be used to include all sorts of image formats in the file; this is the purpose of the "tags" that are included in the header. Many of these tags indicate the simple geometry of the image, like its size, but others define how the data is arranged and various image compression options. For instance, TIFF can be used as a container for JPEG or RLE (run-length encoding) compressed images, and in this respect is completely universal.

However, when TIFF was first introduced, programmers were unwilling to invest the time to support all of the options. As a result the lowest common denominator soon became "the" TIFF, and even today the vast majority of TIFF files, and the code that reads them, are based on a simple 32-bit uncompressed image.

Every TIFF file begins with a 2-byte indicator of byte order: "II" for little endian and "MM" for big endian byte ordering. The following 2 bytes represent the number 42. The number 42 was selected "for its deep philosophical significance". The reading of 42 is dependent on the byte order indicated in the first 2 bytes. The entire file is read based on the indicated byte order.

While TIFF was designed to be extensible, it lacked a core of useful functionality, so that most useful functions (e.g. lossless 24-bit colour) requires nonstandard, often redundant, extensions. The incompatibility of extensions has led some to expand "TIFF" as "Thousands of Incompatible File Formats".