Multispectral Images

[-JKP-]

Put simply, multispectral images are various different photos taken in different wavelengths that are then combined into image files.
This allows different aspects to be contrasted. For example, in space photos, it allows perception to be judged.
The technique has been used on ancient and delicate document (manuscripts, papyrus, even damaged manuscripts IIRC) to produce a contrast between letters and the substance.
As Rene says, if you take a shot in wavelengths that detects iron, you could then contrast ink types.

An important factor to consider is what wavelengths are being used to develop the original multispectral images. The British Library has a system they use You are not allowed to view links. Register or Login to view. where they explain how they use these types of multispectral images to process manuscripts.

Also worth pointing out that jpgs are useless for this sort of thing, a particular bugbear of mine. Why? Because JPG is a "lossy" format that discards original information from the file to save space. The JPG algorithm then guesses what that information was when it recreates the image. So if pixels 1-9 are all a particular type of red, it deletes pixels 2-8 and later tries to guess what sort of red they were.

That's why the Beinecke provide two types of images to download - the smaller JPG and the much larger "lossless" TIFFS, which keep all the pixel information.

TIFF is a good format, widely used in desktop publishing and the printing industry—I prefer it—but JPG isn't always lossy. It depends how it is stored. There are settings for JPG that determine the amount of compression (and loss) and it can be saved as lossless.

Having said that, not every implementation of JPEG has a lossless option. For example, some of the Adobe implementations (which unfortunately affects a lot of software) are lossy and since Adobe is always changing things, it's hard to keep track of which ones they are. I'm not sure why they decided to do this, maybe because they offer so many file formats and assumed users would choose something else (like TIFF) when they wanted lossless.