TIF

TIF (or TIFF) stands for Tagged Image (Graphics) File Format. It is a container that can hold images in a wide variety of bitmapped or even vector formats.

Overview

TIF can also be compressed or uncompressed. If compressed they can use RLE, JPG, LZW, ZIP and potentially other formats like the new JXR. This standard is currently owned by Adobe and is at version 6.0. TIF can even support multiple images in the same file and a mix of bitmapped and vector images. A special floating-point TIF format can store HDR images.

Its main drawback is that it is so versatile that saying that TIF is a supported format may mean nothing since there are really many TIF formats. As a result the lowest common denominator soon became what is called TIFF, and even today the vast majority of TIFF files, and the code that reads them, are based on a 32-bit CMYK or 24-bit RGB uncompressed image. TIFF may be thought of as a container rather that an image format.

XIF

TIF can also support layers of data. As an example, the XIF (eXtended Image Format) file format used by Nuance Communications scanning software (Textbridge) is designed to store text documents as images using an extension of the .TIF format that separates the image into four layers:

1. Text color layer
2. Text layer for OCR (optical character recognition)
3. Layer containing color image segments
4. Background tint layer

File layout

• Every TIF begins with a 2-byte indicator of byte order: "II" for little endian and "MM" for big endian byte ordering.
• The next 2 bytes represent the number 42, selected because this is the binary pattern 101010. The reading of the 42 depends upon the byte order indicated by the 2-byte indicator as do all word, double word, etc. information in the TIF file.

A standard TIF file format uses 32-bit offsets and, as such, file size is limited to 4 GB. BigTIFF is a TIF variant file format, which can contain more than 4GB of data by using 64-bit offsets. Support for BigTIFF file format is limited.

Private tags

Developers can apply for a block of "private tags" to enable them to include their own proprietary information inside a TIF file without causing problems for file interchange. TIF readers are supposed to ignore tags that they do not recognize. Applying to Adobe insures that these tags will be unique.

One such tag has become a standard for Geo-referencing use. GeoTIFF is a public domain metadata standard which allows mapping information to be embedded within a TIFF file. This data is typically geographic latitude and longitude data but other mapping data is supported.

For more information

• http://en.wikipedia.org/wiki/Tagged_Image_File_Format
• See also: Graphics for background data and other formats.
• Lib tiff - contains specifications and more.