Can I archive a TIFF?

TIFF. It’s all the rage these days. All my friends are doing it. Can you?

As with a lot of things in PDS: it’s complicated. That’s why it’s getting a whole blog post. TIFF comes in many shapes and sizes, and we’re here to nail down some specifics for you. Unlike my last post about JPEGs though, there’s some good news here. Spoiler: You can archive most TIFF images, but not all of them.

Here’s the easy part

If you just want to provide some supplementary images in your bundle (in other words, the TIFF images are not your primary observations), the answer is almost certainly, yes, you can archive them. TIFF 6.0 images may be submitted as Documents ¹ or Browse Products², because those have a lot more flexibility when it comes to permitted formats. To be clear: if you’re submitting an image as a Document, it must actual documentation, not the actual scientific result. This isn’t a cheat code!

Under pressure

Now let’s discuss submitting your data as a TIFF image.

TIFF 6.0 was designed with a lot of capability. It includes compression as well as the ability to store both image data and text in the same file. The key consideration is that for long-term scientific archiving, the PDS requires every single part of a data file to be fully described in ways that won’t get lost to time.

As a result, some of the features that TIFF supports cannot be accepted in the PDS. *For example no compression. “Baseline” TIFF itself allows for a few different compression formats, so those must be disabled to make the compatible for the PDS.

While some aspects of TIFF images are not compatible with archiving, pretty much any TIFF can be converted so that it can be archived.

In the end, you’re still going to be working with the primary building blocks to describe the images: Array_3D_Image, for RGB or multi-band spectral, or Array_2D_Image for greyscale mosaic. This structure will be used to define the image’s byte offsets, axis sizes, and data types of each byte of the uncompressed image. That means that if it can’t be described with those, you can’t archive it.

You may archive TIFFs with multiple subfiles, but each must be described by an Image File Directory (IFD), and crucially must also be described individually by its own Array_*D_Image and Header descriptions.

GeoTIFF - still complicated

GeoTIFF is an open source format that includes geospatial information alongside the image data inside the TIFF file. GeoTIFFs store the location of the image so that it can be projected using programs such as ArcGIS. Like baseline TIFF, the same restrictions apply, but if you’re working with this type of data, it can likely be archived as a GeoTIFF! That way, the original tags can be preserved as part of the archive. In fact, we think it’s a great idea to do so, since it will retain compatibility with many tools currently used by the community.

If you want to make GeoTIFFs for archiving, GDAL, an open-source translator library for geospatial data, is able to produce PDS4 labels and check their compliance.

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