TIFF or the Tagged Image File Format is a rather old standard that 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 all prepress software on the market.

TIFF is strictly used for bitmap data. It doesn’t contain text nor vector data, even though its structure would permit additional tags to handle such data.

TIFF was develop 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.

File format specs

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 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/IT is a prime example. I have devoted a couple of of pages to this format. Click here to learn more about it.

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 TIFF. 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 support 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 Gigabytes of raster data. However, this is 4G 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).

Specsheet

Name: TIFF
Developer: Aldus (now: Adobe)
Release date: 1987
Type of data: bitmap only
Number of colors: 2, 4, 8, 16, 32, 64, 128, 256, 32768, 16777216 or 4294967296
Color spaces: grayscale, RGB, CMYK
Compression algorithms: Packbits, LZW, CCITT G3&4 , JPEG (not used right now)
Ideal use: information exchange between prepress applications on any platform
Extension on PC-platform: .TIF (variations exist)
Macintosh file type: ?
Special features: -
Remarks: 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.