TIFF

Tagged Image File Format (abbreviated TIFF) is a file format for mainly storing images, including photographs and line art. Originally created by the company Aldus for use with PostScript printing, TIFF is a popular format for high color depth images, along with JPEG and PNG. TIFF format is widely supported by image-manipulation applications such as Photoshop by Adobe, GIMP, and Paint Shop Pro by Jasc, by desktop publishing and page layout applications, such as QuarkXPress and Adobe InDesign, and by scanning, faxing, word processing, optical character recognition, and other applications. Adobe Systems, which acquired the PageMaker publishing program from Aldus, now controls the TIFF specification.

The phrase "Tagged Image File Format", or, actually, "Tag Image File Format", was used as a subtitle in some earlier versions of the TIFF specification. The current TIFF specification, TIFF 6.0, makes no mention of these phrases; the name is now, simply, "TIFF".

TIFF was originally created as an attempt to get desktop scanner vendors of the mid-1980's to agree on a common scanned image file format, rather than have each company promulgate its own proprietary format. In the beginning, TIFF was only a bilevel image format, since that was all that desktop scanners could handle. As scanners became more powerful, and as desktop computer disk space became more plentiful, TIFF grew to accommodate grayscale images, then color images.

Flexible options
TIFF is a flexible and adaptable file format. It can handle multiple images and data in a single file through the inclusion of "tags" in the file header. Tags can indicate the basic geometry of the image, such as its size, or define how the image data is arranged and whether various image compression options are used. For example, TIFF can be used as a container for JPEG and RLE (run-length encoding) compressed images. A TIFF file can also include a vector-based clipping path (an outline that crops or frames the main image). The ability to store image data in a lossless format makes TIFF files a useful method for archiving images. Unlike standard JPEG, TIFF files can be edited and resaved without suffering a compression loss. Other TIFF file options include multiple layers or pages.

Although it is a widely accepted standard format today, when TIFF was first introduced, its extensibility led to compatibility problems. Programmers were free to specify new tags and options, but not all programs implemented support for all the tags that had been created. 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.

TIFF has an option to use LZW compression, a loss-free technique of reducing file size, however this technique is covered under several patents in different jurisdictions. As of 2005, all but one of these patents has expired, including the most well-known and controversial patent owned by Unisys. The single outstanding patent will expire on August 11, 2006 and is owned by IBM, who has shown no interest to date in enforcing it.

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.

Byte order can cause compatibility issues between Apple Macintosh and Windows programs, which typically use different byte order for TIFF files. Some programs offer the option of saving in Mac or Windows byte order so files can be used across platforms.

TIFF in document imaging
TIFF format is standard in document imaging and document management systems. In this environment it is normally used with CCITT Group IV 2D compression, which supports black-and-white (also called bitonal or monochrome) images. In high-volume environments, documents are typically scanned in black and white (rather than color or grayscale) to conserve storage capacity. An average A4 scan produces 30 kilobytes (KB) of data at 200 dpi (dots per inch resolution) and 50 KB of data at 300 dpi. 300 dpi is far more common than 200 dpi.

Because TIFF format supports multiple pages, multi-page documents can be saved as single TIFF files rather than as a series of files for each scanned page.