Definition of TIF File Extension

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By Paul K. Sholar
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The TIF file extension (also known as TIFF) identifies a file containing digital image data that conforms to the Tagged Image File Format (TIFF), a specification originally authored in the 1980s by Aldus Corporation (later acquired by Adobe Corporation) but later revised and reissued by other organizations for their own uses.
Aldus created the original TIFF format for use by manufacturers of desktop image scanner equipment, to avoid a proliferation of proprietary scanner image formats.
The most recent major version of the TIFF specification, TIFF 6.0, was published in 1992; find a link to the specification below under "References". In 2002, Adobe released the most recent revisions to the 1992 specification. As of 2009, Adobe Corporation holds the copyright to the TIFF specification.
The TIFF format is designed to be flexible. A TIFF file is unlike other graphic file formats in using "tags" to identify the items of image-related information a given file contains, as opposed to requiring a fixed set of information to be stored in a certain order. The meanings and use of some tags are defined in the specification, while others can be defined by the image-writing software. A TIFF file's image header, or Image File Directory (IFD), is an open-ended set of tags that identify only the information that the image-writing software chooses to store.
The flexibility designed into the TIFF specification has resulted in limited compatibility of TIFF files across graphics data applications. Because each image-writing software can create custom tags, no application can be expected to support all of them.
TIFF files tend to be large and can contain many variations of data content, so most web browsers require plug-in or add-on software to display them.

General Features

The TIFF format is the standard storage format for facsimiles (FAXes) because it can save scanned multi-page documents as one file and supports two-dimensional compression of bi-tonal images (that is, all image data is either black or white).
Unlike other graphic file formats, the TIFF format supports several data-compression schemes and color spaces. The TIFF specification supports JPEG compression, LZW, RLE, and others. The format also supports standard color spaces and permits definition of custom color spaces by the image-writing software.
The TIFF format also supports a range of data types, including those that make it appropriate for storing scientific data. A TIFF file can store signed or unsigned integers, floating-point numbers, and complex data.

Special Features

A developer of image-reader or image-writer software can request from Adobe Corporation a block of "private" tags for expressing proprietary information inside a TIFF file. Image-reading software is required to ignore tags in a TIFF file that it does not recognize; therefore, a software developer's private tags are guaranteed not to interfere with private tags defined by others or with tags defined in the TIFF specification.
For an application in which extended precision is required, such as scientific image processing, the TIFF format's "SampleFormat" tag allows storage of integer images with more than 8 bits per channel as well as images composed of floating-point data.

Size of TIFF Files

The TIFF format uses 32-bit offsets; therefore, the size limit for a TIFF file is 4 gigabytes.
As of 2007, the BigTIFF project was underway to implement extensions to the open-source libtiff software library that would support TIFF files of up to 18,000 petabytes in size. For more information, see the link below under "References".
A TIFF file, even after being compressed, is usually larger than a similar GIF or JPEG file.

Color Support in TIFF Files

A TIFF file's data can describe an image with color depth from 1 bit to 24 bits (RGB) to 32 bits (CMYK).
Four baseline image types are available in TIFF files: bi-tonal, grayscale, palette (that is, indexed) and RGB. An RGB image can define up to 16.7 million colors. Palette and grayscale images are limited to 256 colors or shades.
A common extension of the TIFF specification is to support CMYK images.

Considerations for Software Developers

Software developers need not obtain a license from Adobe Corporation to produce software that reads and writes files in the TIFF format. Use of existing software libraries that process TIFF files might require a license agreement.
There are several software libraries that support processing of TIFF files. The libtiff library is free and open-source; find support information at the TIFF and libtiff mailing lists referenced below under "References". The GeoTIFF project has produced the libgeotiff software library, for working with georeferenced raster imagery. The tifficc utility is part of the "little cms" color management engine. For the Python programming language, the Python Imaging Library includes support for TIFF file processing.
A graphics file in the TIFF format cannot be streamed because its blocks of data can be stored in any order, thereby precluding efficient buffering in the software receiving a transmission.
The design of data blocks in TIFF files means that an incorrectly encoded offset stored within the file can result in a buffer overflow error in TIFF image-handling software. Multiple buffer-overflow bugs have been found in the libtiff software library. Each such bug can allow malicious software to execute arbitrary code on the target system, and exploits of such bugs have been reported.