# Hyperspectral Imaging – Seeing The Unseeable

They say that a picture is worth a thousand words. But what is a picture exactly? One definition would be a perfect reflection of what we see, like one taken with a basic camera. Our view of the natural world is constrained to a bandwidth of 400 to 700 nanometers within the electromagnetic spectrum, so our cameras produce images within this same bandwidth.

For example, if I take a picture of a yellow flower with my phone, the image will look just about how I saw it with my own eyes. But what if we could see the flower from a different part of the electromagnetic spectrum? What if we could see less than 400 nm or greater than 700 nm? A bee, like many other insects, can see in the ultraviolet part of the spectrum which occupies the area below 400 nm. This “yellow” flower looks drastically different to us versus a bee.

In this article, we’re going to explore how images can be produced to show spectral information outside of our limited visual capacity, and take a look at the multi-spectral cameras used to make them.  We’ll find that while it may be true that an image is worth a thousand words, it is also true that an image taken with a hyperspectral camera can be worth hundreds of thousands, if not millions, of useful data points. Continue reading “Hyperspectral Imaging – Seeing The Unseeable”

# Hyperspectral Imaging With A DSLR

It’s a relatively simple task to find evidence of helium by just looking at the sun; all you need is a prism, diffraction grating, and a web cam. DIY spectrometers have been around for ages, but most of them only produce a spectrum, not a full image complete with spectral data. Now it’s possible to take an image of an object, complete with that objects spectra using a DSLR, some lenses, a PVC pipe, and the same diffraction grating from your DIY interferometer.

The idea behind a hyperspectral imager is to gather the spectral data of each pixel of an image. The spectral data is then assembled into a 3D data cube, with two dimensions dedicated to the image, and the third dimension used to represent wavelength. There are a surprising number of applications for this technique, ranging from agriculture and medicine to some extremely creepy surveillance systems.

The authors of this paper (freakin’ huge PDF) used a piece of PVC pipe, three camera lenses, a diffraction grating, and a small paper aperture to construct their hyperspectral imager. Images are captured using a standard, multi exposure HDR method, assembling the raw data from the camera into a hyperspectral image with MATLAB.

There’s a ton of awesome info in the PDF, covering how the authors calibrated their system for different lighting conditions, interpreted the RGGB Bayer sensor in the camera, and a few examples of what kind of image can be constructed with this kind of data. That’s a recommended read, right there.

Thanks [Yannick] for the tip.

# Painted Over But Not Forgotten: Restoring Lost Paintings With Radiation And Mathematics

An intrinsic property of paintings, that makes them both wonderful and very annoying, is the fact that they are physical objects. Sometimes they survive across the ages as amazing artifacts of their era, but they are also susceptible to being lost and even destroyed. Sometimes this destruction is deliberate, such as when a painting is painted over.

Artists reuse canvas all the time — painting over what was already there. Sometimes they might be coerced by a client into altering a painting, or removing entire elements from a scene. Fortunately, nowadays we have many techniques, involving x-rays and infrared radiation, that can analyze paintings to determine not only the composition of what we can see with the naked eye, but also that what lies underneath.

In some cases, we can then reconstruct what was previously hidden, returning to physical reality paintings and sketches which haven’t seen the light of day for sometimes centuries. Continue reading “Painted Over But Not Forgotten: Restoring Lost Paintings With Radiation And Mathematics”

# 2015 THP Inspiration: The Environment

It’s not as flashy as Tesla coils or electric vehicles going 200 mph, but the environment is more important than a bunch of cool baubles and sparks flying everywhere. When it comes to this year’s Hackaday Prize, you’re going to need a project that matters, and what’s a better way to do it than with something to help the environment?

While not traditionally a domain that rocks people’s socks, there are a lot of cool builds that can help the environment like this hyperspectral imager that’s a mashup of a spectrometer and a camera, or something that takes an image of an object, complete with the spectral data of each pixel. It’s useful for everything from farming, to forestry, to medicine.

Perhaps you want to get your hands messy by mucking about in the dirt. You’ll probably find something interesting to build for this year’s Hackaday Prize, like the modular farmer’s market we saw in Detroit last year. How about an urban farming and aquaponics setup? Tilapia do well in giant buckets, you know.

If robots are more your speed, then how about an RC tractor or an entire robotic farm? You could always eradicate invasive plants with a quadcopter if flying around is more suited to your expertise. There are plenty of ways to do something that matters for this year’s Hackaday prize, but we’d be lying if we had all the answers. That’s where you come in with your entry for The Hackaday Prize.