Scientists have developed a simple method to calibrate smartphone cameras, an tool that will help amateurs and science students to collect useful research data without specialised equipment. Although smartphones and other consumer cameras are increasingly used for scientific applications, it is difficult to compare and combine data from different devices.
“The low cost of consumer cameras makes them ideal for projects involving large-scale deployment, autonomous monitoring or citizen science,” said Olivier Burggraaff, who led the research team from Leiden University in the Netherlands. “Our standardised calibration method will make it easier for anyone to use a consumer camera to do things like measure pollution by detecting aerosol particles in the air,” said Burggraaff, who developed the calibration method.
In the journal Optics Express, researchers described the method called SPECTACLE (Standardised Photographic Equipment Calibration Technique And CataLoguE), which can be used for smartphones, digital single-lens reflex cameras and cameras aboard drones. The database allows users to upload calibration data from their cameras for others to use.
“SPECTACLE includes many do-it-yourself (DIY) methods, which we found provided results comparable to professional methods that require high-end laboratory equipment,” said Burggraaff.
The standardised calibration method was developed in response to a need that arose as researchers were developing citizen science methods to measure optical water quality using a smartphone.
“To use smartphone cameras to measure water quality we need to understand them well because each manufacturer and each device has its own characteristics,” said Burggraaff. “SPECTACLE brings together many existing calibration methods and applies them for the first time to consumer cameras, which will make it much easier for other developers and for us to use these cameras for scientific purposes,” he said.
To test the new calibration methods, the researchers compared them with established methods using several cameras. They found, for example, that the DIY method for measuring how the lens distributes light on the sensor, known as flat fielding, matched within five per cent of results from the standard method that requires an integrating sphere in a laboratory setup.
The DIY method involved taping paper on the camera and acquiring images of the Sun or a computer screen. The researchers plan to apply the SPECTACLE methodology to a much larger number of cameras to fill in the database and get a broader idea of camera properties. This will be done by the researchers as well as anyone who wants to upload their calibration data into the database.
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