Thermal imaging in Film and TV

Person through a thermal camera

In 1987, audiences were wowed by Predator; not just because of the muscled cast, gratuitous violence and cheesy one-liners, but for the special effects: the eponymous antagonists' technology - invisibility and thermal vision. Whilst invisibility is not yet possible, thermal imaging is not only real but is growing in popularity: in more recent years it has been notably featured in Sicario and Planet Earth II.

Like many things, new and exciting technologies stem from military development. The obvious military application is the ability to completely negate camouflage and detect both infantry and vehicles alike. Many other industries have since benefited from this technology, notably medical and construction.

Thermal imaging (called thermography) isn't dissimilar from night vision, however it differs in that it can be used both day and night. Traditional night vision is done in one of two ways or a combination of both. Active illumination is where an infrared light (one that emits light just beyond that of the visible spectrum) is shone onto a target area. Some camera sensors are sensitive to this spectrum and so can actually see this light. Try pointing a TV remote at your mobile phone camera and pressing a button - you'll likely see a violet coloured flash - this is the infrared LED transmitting a signal. Not all cameras can see this spectrum however; many stills and video cameras actually have a filter in place over the sensor to block the infrared spectrum as this can pollute the colours of the visible spectrum, resulting in pictures with odd colour casts. Active illumination is a cost effective method of night vision, well suited for CCTV and similar applications. However where it isn't so suitable is in military use:  what good is a night vision device if it emits light visible to a camera? It wouldn't be any different from simply using a torch to see in the dark - completely giving away your position! Night vision goggles for instance use another form of technology called light intensification. This simply uses available light such as from the moon or stars and greatly boosts it to a visible degree. It's similar to cranking up the ISO on a digital camera - the image gets brighter, albeit noisy. The methods of how it does this are beyond the scope of this article, but suffice to say it's a bit of scientific wizardry.

The trouble with both of these night vision methods is that they can only be used at night or in dark conditions and are dependent on an existing source of illumination. Finally, if the person or animal is camouflaged amongst it's surroundings, not matter how bright the image is - they'll still be hidden. Thermal imaging however does not have any of these limitations.

Everything above absolute zero (0ºK/-273.15° C/-459.67° F) - in other words, everything - gives off infrared radiation - the hotter it is, the more it gives off. Thermal cameras today have a specific sensor called a microbolometer and it detects this radiation in the long wave infrared spectrum, hence why thermal cameras are often called infrared cameras and confused or associated with night vision. For those that are interested, the visible light wavelength is 400-700 (violet through to red) nanometers in width; night vision 'sees' 700-1000nm wavelengths (just past visible red, hence the name infrared) and thermal imaging detects 8-14µm (micrometer) wavelengths (8000-14,000 nanometers/0.008-0.014 millimeters).

Thermal cameras are typically thought to be prohibitively expensive. Traditionally, this was the case, however as the technology advances, the devices are getting both more affordable and higher in quality. The microbolometer is one of the main reasons why a thermal camera costs significantly more than a counterpart 'visible light' camera: it's a completely different type of sensor, of which the technology simply hasn't advanced as fast or as far as a regular digital camera sensor has. Cinema cameras today such as the RED Weapon are shooting in 8K (8192 x 4320) and even mobile phones are now shooting in 4K (3840x2160), so you may be surprised to hear that the very best thermal cameras commercially available today are not even HD. The cameras used on Planet Earth II and Sicario were borrowed military bits of kit and even so were only 1920x1080. 1024x768 seems to be the highest resolution thermal camera you can actually buy - and for a five figure sum. Furthermore, these products are specialist tools for industrial use (gas and electrical for instance) and are not suitable for filmmakers for a number of reasons.

Thermal cameras can't see through glass
Glass blocks long wave infrared radiation
The other reason thermal cameras are so expensive is often overlooked: the lens. Glass blocks the wavelengths detected by a microbolometer, meaning the lenses need to be constructed out of an alternative (and costly) material - germanium. It also means that you can't see (or be seen!) through windows and into people's houses. Furthermore, it should be noted that despite any misconceptions, a thermal camera can't see through anything - it's not an X-ray camera! A direct line of sight is needed for the camera to detect a heat signature. The exception to this is if something is hiding behind cover and is in contact with it, this may cause the cover to warm up which could register on the camera. In reality this isn't very common and the cover would have to be fairly thin... such as a cardboard box.

Thermal FS7
Thermal imaging camera mounted on the Sony FS7. Note that Indy has warmed the box up but you still can't see through it.
So how are thermal cameras useful to filmmakers? Well, the appeal is certainly clear - it's a unique way of visualising something that is rarely seen on the big screen. The technology involved means that the most suitable thermal cameras for filmmakers are actually ones designed for hunting and wildlife. Wildlife documentaries of course will probably see the biggest benefit and application for thermal imaging, though I'm sure some filmmakers will find alternate, inventive uses for the seldom seen spectrum. These wildlife cameras are fortunately very light and portable - essentially resembling a digital scope or monocular. Furthermore, they're within the realms of affordability, with the best models costing a few thousand pounds. These top of the line models are suitable for filmmakers for a number of reasons. Firstly, they offer the highest resolution in class, a whopping 640x480. This sounds rather pitiful in today's era of high definition cameras and televisions, however this can be easily and acceptably upscaled to HD. Some models feature built in photo and video recording (until very recently, thermal cameras were typically passive and could not record, or at best recording was possible via video out and an external recorder) and some can even stream wirelessly to your smartphone or directly to the internet. Frame rate is one of the other factors that only in the very recent years and months has become suitable for serious film work.

Deer in a field on a thermal camera
The thermal camera can display in white hot, black hot or various colour spectrums including rainbow, aka 'predator vision'!
Since late last year, I have been heavily involved working on a wildlife documentary called The Tigers of Scotland. It's about one of the rarest mammals on the planet, the Scottish Wildcat. Early on, we realised that we stood little chance of finding this elusive animal without the aid of thermal imaging. Attempting to hire one proved nearly impossible - there is almost nobody out there that actually stocks thermal cameras for film and TV work and in the end we decided to bite the bullet and buy one ourselves. It proved instrumental in our search - the ability to know, objectively, if there was any wildlife in the area or not, plus it's quite an incredible sight seeing an entirely different world that you simply would have otherwise missed. Animals come out at night: the fields were crawling with mice and voles, whilst deer and rabbits appear seemingly out of nowhere. It's fascinating just watching the ground and the trees warm up during the day and cool down at night, and even in built up areas see how house roofs absorb and retain warmth, who has their fire lit (the chimneys heat up!) and which parked cars have been driven recently.

Thermal camera
Cars, people and even recently driven vehicles can be identified with thermal imaging
Being designed for wildlife and hunting, these thermal cameras tend to have lenses on the longer end of focal lengths. For a wildlife documentary, that may well be to your benefit however interchangeable lenses are available for a wider field of view. The range of the camera is quoted at nearly two kilometres - the distance at which a man sized target can be detected and seen. And the camera's resolution is the only limiting factor to this; a thermal camera is not affected by fog or smoke or haze or any other atmospheric conditions that a normal camera might be.

Thermal imaging technology will only get better and I predict we'll be seeing it more often on our TVs and in our cinemas. It's a unique tool that can help communicate stories in a way that nothing else can match. In coming years we'll see thermal cameras more readily available at more affordable prices - and at higher resolutions. Maybe by the time we're all shooting 8K or 12K on our mobile phones we might have HD or 4K thermal cameras! Until that day, if you would like to try filming thermal imagery for yourself, mine is available through my company Wild Films Ltd.

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