How to choose a camera for drone imaging

Credit-Sony


Seven considerations that will help you get the quality you need, faster and with fewer headaches

UAVs have transformed how aerial photography and video are captured, and they are now used for everything from scientific research to filming stunt scenes, and from security to mapping.  But, with such a large number of applications, there can be no one-size-fits-all solution. Here are seven considerations when selecting a camera to get a better image from your drone.


Author: Yasuo Baba, director of digital imaging for Sony Europe URL: www.sony.eu/businesssolutions


Virtually since their inception, UAVs have revolutionised the capture of still images and video for countless industries. Indeed, by them being unobtrusive and getting close to the action – images from drones have become a standard part of sports broadcast and film production process – enabling overhead shots, or getting into the action, without the need (and cost) of a helicopter.

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They have also been used to improve the performance of elite athletes, including being declared Team New Zealand’s “secret weapon” during their victorious 2017 America’s Cup sailing campaign. Elsewhere drones are used for mapping, for scientific site surveys, for security, for disaster management, for maintenance inspection, for wildlife monitoring… the list feels endless.


The WingtraOne is a VTOL mapping drone offering unprecedented coverage and accuracy for survey, mining and other industries.

But with so many applications, there cannot be a one-size-fits-all camera selection. So, what are the critical elements in the decision that should be considered when selecting a camera to get the right shot, first time and without a headache?


1) Sensor size (resolution and sensitivity) In applications such as mapping, the required accuracy can go below even one centimetre, so the camera’s resolution is one of the most essential elements in the drone system.
Indeed, resolution (the number of pixels) is almost always among the first consideration in any application. But it’s not simply a case of higher pixel counts being better.


Increasing resolution can decrease image quality. This is because resolution can be increased in two ways: 1) increasing the sensor size and creating more space for pixels. Or 2) by increasing the pixel density.
By taking the first approach, you typically increase the camera’s size, which affects aerodynamics and weight, and therefore drone flight time (see below). 


By taking the second approach, you reduce the amount of light reaching each pixel (sensitivity), which reduces the ability of the camera to take high-quality images in less-than-perfect light conditions. For applications like security – and even professional film production – a camera with high sensitivity (around ISO 80-102,400) should be sought.
Regardless of the application, the selected camera should ultimately use the largest sensor it can whilst staying within the additional needs of the project. 


For the overwhelming majority of applications, there are, therefore, two primary sensor sizes that should be considered: APS-C (23.6×15.6mm) and full-frame (36x24mm). These are both found in the leading professional mirrorless cameras and will give a much higher image quality for a given resolution.  This doesn’t cover every application, however. 


There will still be a number of applications that require ultra-light, ultra-compact cameras. This needn’t be for flight-range reasons. In fact, it will rarely be for flight-range reasons. A good example might instead be when drones are undertaking indoor inspection – film-makers are also beginning to use drones indoors for some scenes. There is not only a confined space in such use cases, but the drones are also likely being used close to people* or sensitive equipment: by reducing weight, you reduce the force and potential damage caused by a potential accidental impact.
For such applications, where resolution and/or sensitivity can be sacrificed slightly to save weight, we typically say a one-inch sensor (but no lower) should be adopted. 


However, if anything, you should be even more careful when selecting a camera with a smaller sensor. Make sure whichever camera you choose, a holistic design approach has been used (see section 6). This ensures every component – the sensor, the image processor, the lens, the housing – works together optimally. Some great cameras can deliver these exceptional weight savings and still take great images – the 132g (inc batteries) RX0 II, for example, will take 4K video. But be careful and evaluate the camera well. 


2) Required flight time As we touched on above, as you increase the sensor size, you increase the camera size and weight, which has a knock-on effect on flight time. Depending on the application, this effect may be inconsequential: a wind turbine inspection drone will be making short flights but requiring high-detail images so sensor weight and camera size can be increased, and a full-frame sensor (or even bigger) is ideal here. 
Or it may be highly consequential: a drone used to fly alongside boats in The America’s Cup will need to run for about 30-40 minutes at a time and reach speeds of up to 63 mph (101 kph) whilst being buffeted by winds and turbulence, meaning weight is crucial. 

In the middle are applications, such as mapping, such as scientific surveys that take multiple still images and stitch them together. For this, flight times need to be as long as possible, but using a camera with a larger sensor (coupled with automation software – see section 4, below) will allow the same area to be captured more quickly. 


One of the best studies to quantify the effect of weight on flight time in professional-grade drones comes from the mapping drone manufacturer Wingtra. In the study, the company flew their WingtraOne VTOL (vertical take-off and landing) drone and compared the flight times and mapped area using the Sony RX1R II (507g + unspecified lens, 42MP, full-frame sensor) and the Sony ILCE-QX1 (216g, 20MP, APS-C sensor).  

Image copyright Wingtra

The RX1R II’s additional weight reduced the WingtraOne’s flight time by 12% (from 59 minutes to 52 minutes). But, by being able to capture much more ground with each image, the full-frame camera covered an area 29% greater than the APS-C camera (from 310 hectares to 400).For drones undertaking longer flight times, we’re typically asked for the weight of the camera housing and lens to be in the region of 600g. This has traditionally meant an APS-C camera – for example, the 503g ILCE-6600 digital mirrorless camera with lens – has been recommended. However, recent advances in housing technologies have enabled full-frame cameras to come below this. The industry’s lightest is the 24.2 megapixel (4K video) ILCE-7C, which weighs 509g, including the FE 28-60mm F4-5.6 zoom lens pack and batteries.

3) Required flight time – part 2 Beyond weight and aerodynamics, there is a second way a camera choice can affect flight time. Some cameras, explicitly designed to be part of the drone, rather than an interchangeable unit, are powered by the drone’s battery supply rather than their own internal cell. 


While lighter, these cameras tend to use smaller sensors and give poorer quality images. They also often operate using the drone’s battery, which will, in turn, reduce flight time anyway.


4) Inflight control and automation As camera hardware advances, so does software. Over the past decade, several companies have launched companion applications and software development kits to control specific features. During the past 18-24 months, these have become particularly advanced, with virtually every facet of the camera now open to remote control and automation. In content creation for movies, this might be used in a stunt scene, switching from a tightly-focused to a wide-angle shot as the drone changes altitude or changing from standard to ultra-high frame rates when a trigger event occurs. 


In mapping, this automation can be used to control the location and the settings to get the most usable image.
When selecting a camera, try to think about the functions you require. Do you need it to fire based on preset timings or react to external triggers such as a GPS location? Or light levels? And what functions? Do you need to develop your own application via the SDK? Or will the companion app suffice?

5) Lens portfolio The lens selection is critical. Mapping requires a wide-angle lens to capture as large an area as possible. Security requires the ability to both scan large areas and also focus closely on a subject. In broadcast, the lens selection affects the entire feel of the footage.


6) Image processor It’s relatively easy to overlook the image processor. Don’t. The image processor is more than just a CPU and, as such, is often described as being the brain of the camera. 
Done well, the image processor is an aggregation of processors and additional hardware that have been specifically designed and optimised for the camera. 


Try to adopt a camera that has used a holistic approach, developing the sensor and other components in conjunction with the image processor. This will allow the camera to compress images more effectively, take images from the sensor more quickly, improve the readout speed, minimise the rolling shutter effect, and enable a better auto-exposure, auto-focus and auto-white balance response. 


Again, the choice of camera and image processor combination depends on your application… but ignore this consideration at your peril. 


7) Dynamic rangeDrones are used outdoors in all parts of the world. Whether it’s in a disaster zone following a monsoon, out at sea following a race, or on a film studio lot whilst moving in and out of shadows, the lighting conditions can change quickly, and the camera needs to be able to respond accordingly. To manage this, choose a camera with a wide dynamic range. 

ConclusionUAV imaging has revolutionised many imaging applications, but at the heart of all of these is the need to get the right images, at the right quality, in as short a time as possible and with as little frustration as possible. 
By following these tips, you should avoid that headache.


* The FAA (among other aviation authorities) stipulates that commercial drones are not purposefully flown over people without a waiver. 

About the author: Yasuo Baba is the director at Sony Europe BV, responsible for the organisation’s professional digital imaging division. He has more than 20 years of experience in senior management positions at different market-leading technology companies. Sony is a market leader in full-frame, full-frame mirrorless cameras, and lenses also on the European market.

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