TIFF is the most comprehensively capable format for image data, supporting nearly any kind of components. Let’s dive in and see how it does that.
The Tagged Image File Format (TIFF) is an all-purpose container format that supports a nearly infinite variety of image types and component combinations. The name of the format gives a clue to its power. TIFF does very little to specify image encoding, but instead provides a flexible framework for the storage of complex image objects through the robust use of tags. Although the most recent TIFF specification dates back to 1993, it’s possible to include nearly all innovations in imaging technology in a saved TIFF.
IFD
The key to TIFF’s flexibility is the Image File Directory (IFD) structure of the file. TIFF was designed to be extensible, allowing new imaging components to be defined and added as a “subfile.” As new methods of image compositing, adjusting and other manipulations were developed, it became possible to save this data into TIFF by defining a new IFD structure. This has allowed TIFF to support image features that were not even contemplated at the date of the last written specification.
Note that many of the components that can be saved in a TIFF may be proprietary and only “understood” by one specific application. For instance, adjustment layers that can be saved in a TIFF by Photoshop typically cannot be understood by other applications. This could create a problem for interoperability if not for the requirement of a baseline image as described below.
The baseline image
There is another feature of TIFF that has led to its wide adoption as the most capable and compatible image container. The TIFF specification requires that whenever there are multiple components included in a TIFF, there is always a full-resolution, full quality composite of the finished image in the file. This composite is supposed to conform to certain standardized characteristics for pixel layout, color and compression. By including this baseline image, TIFF remains technically compatible with any other program, even if the rest of the TIFF is filled with incomprehensible IFD components.
The gold standard for archives
The IFD structure along with the required baseline image make TIFF an extremely popular choice as an archival image format. TIFF has long been considered the gold standard for archiving. For images that began their digital lives as traditional RGB scans, this remains true.
However, the popularity of digital cameras as image capture devices has begun to change this calculation. Traditional TIFF images are not designed to support the original data in camera raw files. Therefore, converting camera raw originals requires that a destructive transformation be applied to the raw data in order to create the TIFF. In order to also save a copy of the original image data, it’s necessary to save an additional file, or to save the raw data into an IFD inside the TIFF, which is not a standardized operation.
We will see how DNG addresses the shortcomings of TIFF as a camera raw archive file a little later.
Format details
Interoperability
As outlined above, a properly-created TIFF file should be widely compatible with many applications and operating systems, even when subfile IFDs are not understood by the application. The TIFF specification requires that IFDs which are not understood be ignored when opening, but should be preserved if the full TIFF is saved into a new layered file. Because TIFF supports a wide array of color models and bit depths, it’s possible that certain applications will be unable to open a TIFF file because the program does not understand that color model (e.g., a CMYK TIFF may be unreadable to a web browser).
Supported color models
TIFF supports most common (and uncommon) color models, including indexed color, grayscale, CMYK, RGB, LAB and more. TIFFs support bit depth up to 32 bits per channel.
Compression
The original TIFF specification had a handful of limited options for compression, primarily LZW compression. Newer imaging applications may offer ZIP or, depending on the underlying image settings, JPEG compression. ZIP and JPEG are less common and may produce a file that is unreadable to older applications. For maximum compatibility, particularly in files for archives, it’s best to avoid using any compression. Note that saving TIFF files with all their IFD layers intact will make files significantly larger than a flat file with no additional image subfiles. Although these files can become quite large, it’s often desirable to preserve all adjustment layers and subfiles in the master copy of the image file.
Support for additional components
TIFF has virtually unlimited support for subfile components, and is typically limited by the capabilities of the application making the TIFF.
File size limitations
Traditional TIFF files must be smaller than 4GB in total size and may not be longer than 30,000 pixels on any one side. If a larger file is required, the BigTIFF or, more commonly, PSB (Photoshop Big) file formats can be used.
Variants
In addition to BigTIFF mentioned above, there are a handful of variants of the TIFF format.
TIFF/EP
TIFF/EP is a version of TIFF that is designed for electronic photography. It was an early attempt at standardizing an IFD and tag structure for digital cameras. The TIFF/EP specification has been replaced by the more structured and formalized DNG specification.
PSD
The Photoshop Document (PSD) file format is a variant of TIFF that specifies certain characteristics that are useful when working with images in Photoshop. For the vast majority of purposes, PSD and TIFF can be used interchangeably. PSD will offer some advantages in smaller file size compared with TIFF.
The main file size saving with PSD is the ability to forgo the composite image when saving a PSD. Since Photoshop has the ability to reconstruct the finished image from the component parts, Adobe allows PSD files to be saved without the composite final image. While this can offer significant file size savings, it does so at the expense of compatibility. PSD files without the composite image can only be viewed in Photoshop, and run a much greater risk of being incompatible with other software. When saving PSD images, I strongly suggest checking the Maximize Compatibility checkbox as shown below.
When working in Photoshop with motion image files, it’s often advisable to save as PSD rather than TIFF since the format is being continually optimized to effectively handle motion image editing components.
Best uses for TIFF files
Master edit files
TIFF is an excellent choice for master rendered files like those made in Photoshop. TIFF’s support for multiple components allows it to function very much like a project file where multiple components can be saved. But TIFF has the advantage of also having a widely accessible finished version inside the file as well. TIFFs are great for both the works-in-progress phase of the workflow as well as archiving the final image.
Delivery of high quality images
Due to lossless compression and wide compatibility, TIFF is a very popular choice for delivery of finished images. However, when the finished image is a flat 8-bit RGB file with no alpha channel, a JPEG can provide the same level of quality at a much smaller size.
Storage or delivery of color models not supported by other images - CMYK, CIELAB, Duotone or other color models not supported by JPEG or PNG should typically be saved and delivered as TIFF.
Image archiving
TIFF is considered the safest format for long-term image archiving, especially for images greater than 8 bits per channel.