Therm-App Info

The device I'm using is a Therm-App: http://therm-app.com/

The somewhat confusingly-named Therm-App is not an "app", but a hardware device that communicates with an Android device via USB. To use the Therm-App, you install a software app from Google Play store, called "Therm-App: Basic". The makers of Therm-App have made available their SDK to encourage development of other apps for the device, and a few third-party apps are starting to be available.

The Therm-App with a 19mm lens, attached to the back of a Nexus 7 tablet.

By default, the device comes with a 19mm lens, but a number of lenses are now available with the following specs:

Focal Length	Relative Aperture	Field of View	35mm equivalent
35mm	f/1.14	10.5° x 7.9°	200mm
19mm	f/1.1	19° x 14°	105mm
12.8mm	f/1.0	28.8° x 21.7°	70mm
6.8mm	f/1.41	55° x 41°	35mm

The standard 19mm lens has pretty good range for detection, though not detail unless the subject is pretty big or pretty close. The 35mm lens is expensive, but after finally deciding to splurge, I've had no regrets: the increased range has yielded better detection and details. The trade-offs are a narrower field of view and more dizzying "camera shake".

In The Field

Using an infrared camera in the field is akin to using a metal detector: after the novelty factor wears off, it quickly becomes tedious with only the prospect of discovery motivating further usage. What happens is you end up staring at the screen the whole time, sometimes having to stretch yourself to stare at high angles:

To allay this, you can use a longer cable to point the camera independently of the screen:

a situation that could conceivably be aided by a selfie-stick, but you're still staring at a screen as you walk rather than taking in the natural surroundings. To alleviate this, I've tweaked the software with an experimental hotspot detection algorithm than plays a sound when something is detected (more below).

Once something is sighted, there is the cumbersome step of trying to look through the binoculars while holding the device:

which seems to work pretty well, but quickly becomes cumbersome when I need to then pull out my camera for a shot. (On my to-do list is to fashion some kind of holster to hold the Therm-App device.)

Software Development

After my initial dabbling with the device, I decided to get the SDK and see if I can't address some of the shortcomings of the device and of the "Basic" app. I'll chronicle here some of the experiments I've done on this front. As you peruse this blog, keep in mind that some of it will be using my experimental app. If you would like to experiment, it is available at http://suan-yong.com/ir/therm_wild.html, but note that it is unpolished and I have little time for tech support or making cosmetic improvements.

Background Filtering

The most significant change so far is background filtering, which allows one to take a snapshot (of a blank surface) to serve as a background filter that is subtracted from every frame from the device. I have found that this cleans up a significant amount of noise, especially when the device is used in cold temperatures.

A group of people gathered around a campfire in the woods. The image below is raw while the image above is filtered by a background frame.

Hotspot Detection

I've also started trying various algorithms to detect hotspots, and will play an alert sound when a hotspot is detected. This allows me to walk around pointing the device variously without staring at the screen the whole time.

Color Palettes

Next up on my to-do list is to experiment with different color palettes. In particular, I want a palette that only shows hotspots in bright (yellow), but stretches the remaining temperatures across a wide spectrum of medium-to-low brightness hues, to maximize contrast and detail (thus hopefully to facilitate identifying "landmarks" to help locate the detected hot subject).