The TIFF file format

TIFF or the Tagged Image File Format is a file format that is strictly used for bitmap data. TIFF files don’t contain text or vector data, even though the file format theoretically would permit additional tags to handle such data. Despite being one of the earliest file formats for images, it is still very popular today. It is a highly flexible and platform-independent format which is supported by numerous image processing applications and virtually all prepress software on the market.

The file extension for TIFF files is .tif even though .tiff is also used occasionally.

File format specifications

As the name implies, TIFF images make use of tags, keywords defining the characteristics of the image that is included in the file. For example, a picture that contains 320 by 240 pixels would include a ‘width’ tag followed by the number ‘320’ and a ‘depth’ tag followed by the number ‘240’.

The flexibility of TIFF makes it very easy to write a TIFF-writer, but very difficult to create a fully TIFF compliant reader. The need for well-defined rules has caused a few TIFF-substandards to appear. For prepress, TIFF/ITTIFF/EP, a version of TIFF optimized for digital photography.

 is a prime example but that file format is no longer actively used. Another substandard is

Color spaces

TIFF images can contain more or less anything:

• Line-art (pure black-and-white)
• Grayscale
• Pseudocolor, from 1-bit to 8-bit (also called palette color or indexed color in Photoshop)
• RGB
• YCbCr
• CMYK
• CIELab

For grayscale, RGB and CMYK images, 8 bits (256 levels) are used per channel but this is not a limitation of the TIFF file format. The file specifications also allow 16-bit channels. Although this feature is also supported by recent versions of Photoshop, many layout applications and drivers cannot yet support these data types.

Compression

TIFF supports a large number of compression algorithms. The lossless algorithms that can be used are:

• PackBits
• LZW (Lempel-Ziv-Welch), popular for grayscale or color images (although it is not very efficient for CMYK images)
• CCITT Fax group 3 & 4, mainly used for line-art images (especially screened data coming from a RIP or copydot application).

Officially TIFF also supports lossy JPEG compression. Unfortunately, the specs were not worked out correctly and JPEG never gets used in TIFF files, at least not for prepress use.

File size

TIFF files cannot have more than 4 Gigabyte of raster data. However, this is 4GB of compressed data, and so if the compression ratio is high enough, theoretically a TIFF image could be much larger (in fact, 2**32-1 pixels square).

How to edit TIFF files

All professional image editing applications on the market are capable of opening TIFF files. My favorite is Adobe Photoshop.

How to convert TIFF files

There are tons of converters that can convert a TIFF file to a JPEG, PNG, EPS, PDF or other file format. Google is your friend.

• I have in the past had good experiences with GraphicConverter, a shareware tool for Macintosh that can import about 200 file types and export 80.
• For occasional file conversions I stick to Photoshop – it is not too difficult to write an action that does a batch conversion of a series of files.
• To convert a series of TIFF files to a PDF using Adobe Acrobat Professional 9: select File > Combine > Merge Files into a Single PDF. The Combine Files dialog box pops up. If you want to preserve the original image resolution, be sure to select the largest page icon that appears in the most lower right-hand corner listed next to ‘File size:’.

The history of TIFF

TIFF was developed as a universal image file format by Aldus (makers of PageMaker) in 1987. The most recent specifications, TIFF 6, were released in 1992. It is pointless to study older versions of the format since everybody sticks to the TIFF 6 specs. Since then, Aldus has been bought by Adobe so Adobe now holds the copyright. They have not released any new versions of TIFF which is not necessarily a bad thing since standards that last long are well supported and understood in the market.

Other sources of information

Niles Ritter maintains an unofficial TIFF home page. It covers various aspects of the file format and also points to the rather hefty TIFF 6 specifications you can download from the Adobe web site.