TIFF compression? Use discretion! | Open Preservation Foundation

The British Library’s Digital Preservation Team is sometimes asked to help resolve the preservation planning challenges of Library colleagues and other organisations. This post describes a recent request for assistance, the steps taken to learn more, the conclusions reached, and where this leads us next.

The TIFF format and lossless compression

The TIFF image format is generally regarded as the gold standard for long-term storage of static image data. It is flexible, widely supported, and rich in its treatment of both image data and metadata. Its historical disadvantage has been its large file sizes; this can, however, be mitigated by the use of compression, support for which is built into the format and described in the TIFF compression tag for each file.

The method most commonly used to compress TIFF files is the Lempel-Ziv-Welch algorithm, or LZW, which has been supported since 1988. Since then support has been introduced for other compression methods, including the one which we were asked to investigate as to its effectiveness – namely Deflate, more commonly referred to as Zip compression. Zip compression has been widely implemented since its initial development, due primarily to the fact that the general algorithm itself remains unpatented. LZW, by contrast, remained under patent util 2003, limiting its widespread adoption except where used under license.