Tagged Image File Format Totally Explained

Everything about Tagged Image File Format totally explained

Tagged Image File Format (abbreviated TIFF) is a file format for storing images, including photographs and line art. It is now under the control of Adobe Systems. Originally created by the company Aldus for use with what was then called "desktop publishing", the TIFF format is widely supported by image-manipulation applications, by publishing and page layout applications, by scanning, faxing, word processing, optical character recognition and other applications. Adobe Systems, which acquired Aldus, now holds the copyright to the TIFF specification. TIFF hasn't had a major update since 1992, though several Aldus/Adobe technical notes have been published with minor extensions to the format, and several specifications, including TIFF/EP, have been based on the TIFF 6.0 specification.

History

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-1980s 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 binary image format (only two possible values for each pixel), 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. Today, TIFF is a popular format for high-color-depth images, along with JPEG and PNG. Adobe Systems, which acquired the PageMaker publishing program from Aldus, now controls the TIFF specification.

Flexible options

TIFF is a flexible and adaptable file format that handles images and data in a single file via inclusion of file header tags that indicate the basic geometry of the image (size, definition, image data arrangement, and applied image compression options). For example, a TIFF can be a container file holding compressed JPEG and RLE (run-length encoding) images. A TIFF can also include a vector-based Clipping path (outlines, crops, frames the image). The ability to store image data in a lossless format makes TIFF files a useful image archive, because, unlike standard JPEG files, a TIFF using lossless compression (or no compression) may be edited and resaved without suffering image compression loss; other TIFF options include layers and pages.
   Although it currently is the accepted standard format, when TIFF was introduced, its extensibility provoked compatibility problems. Programmers were free to specify new tags and options, but not all implemented programs supported all created tags. Resultantly, the TIFF soon became the lowest, common denominator, still, today, the majority of TIFFs, and the code that reads them, are based on an uncompressed 32-bit CMYK or a 24-bit RGB image.
   The TIFF offers the option of using LZW compression, a lossless data compression technique for reducing a file's size. Until 2004, this option's use was limited, because the LZW technique was the subject of several patents; however, these patents are expired.
   Every TIFF 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 "for its deep philosophical significance". The reading of 42 depends upon the byte order indicated by the 2-byte indicator. All words, double words, and so on, in the TIFF file are read based upon the indicated byte order. The TIFF 6.0 Specification (Section 7: Additional baseline TIFF Requirements) writes that compliant TIFF readers must support both byte orders (II and MM), however, TIFF writers may choose the byte order most convenient for their image purposes. The image-processing community's joke about the TIFF's standardised-consistency problems in its early variations was Thousands of Incompatible File Formats.
   The Tiff file format uses 32bit offsets, and as such, each file is limited to 4 gigabytes.

TIFF in document imaging

TIFF format is standard in document imaging and document management systems. In this environment it's 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 ppi (pixels per inch resolution) and 50 KB of data at 300 ppi. 300 ppi is far more common than 200 ppi.
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.

TIFF in scientific imaging

The inclusion of the SampleFormat tag in TIFF 6.0 allows TIFF files to handle advanced pixel data types, including integer images with more than 8 bits per channel and floating point images. This tag made TIFF 6.0 a viable format for scientific image processing where extended precision is required. An example is the use of TIFF to store images acquired using scientific CCD cameras that provide up to 16 bits per pixel of intensity resolution.
Storing a sequence of images in a single TIFF file is also possible, and is allowed under TIFF 6.0, provided the rules for multi-page images are followed.

Private tags

Developers can apply for a block of "private tags" to enable them to include their own proprietary information inside a TIFF file without causing problems for file interchange. TIFF readers are required to ignore tags that they don't recognise, and a developer's private tags are guaranteed not to clash with anyone else's tags or with the standard set of tags defined in the specification.

Exploits

The TIFF file format is unusual in comparison to other image formats, in that it's composed of small descriptor blocks containing offsets into the file which point to the actual pixel image data (composed of bands of pixel rows). This means that incorrect offset values can cause programs to attempt to read erroneous portions of the file or attempt to read past the physical end of file. Like most other image file formats, improperly encoded packet or line lengths within the file can cause poorly written rendering programs to overflow their internal buffers. Properly-written image rendering programs generally avoid such pitfalls.
Multiple buffer overflows have been found in libtiff,(External Link

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) some of these have also been used to execute unsigned code on the PlayStation Portable,(External Link

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