Scientific research with any smartphone camera
Although smartphones and other consumer cameras are increasingly used for scientific applications like citizen science, it’s still difficult to compare and combine data from different devices. PhD student Olivier Burggraaff developed a new easy-to-use standardised method which makes it possible for almost anyone to calibrate these cameras without any specialized equipment. That way, he helps amateurs, science students and professional scientists to acquire useful data with any consumer camera.
DIY methods
‘The low costs of consumer cameras make them ideal for projects involving large-scale deployment, autonomous monitoring or citizen science,’ says Burggraaff, PhD at the Leiden Observatory and the Institute of Environmental Sciences Leiden. He led the multi-institutional research team that developed the calibration method. ‘Our standardised calibration method will make it easier for anyone to for example grab their smartphone and assist in measuring pollution by detecting aerosol particles in the air.’
The team reported their new standardised calibration method and database in Optics Express, the journal of the Optical Society. The method is called SPECTACLE (Standardized Photographic Equipment Calibration Technique And CataLoguE) and 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,’ Burggraaff adds.
DIY vs laboratory
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 5 percent 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.
Improving citizen science
Burggraaff and his colleagues developed the calibration method in response to a need that arose when they were developing citizen science methods to measure optical water quality. They used a special smartphone add-on called iSPEX (Spectropolarimeter for Planetary EXploration), which they originally developed to measure air pollution. With iSPEX, a smartphone camera can measure complementary optical information, such as hyperspectral and polarimetric data.
‘The problem is that each manufacturer and each device has its own characteristics,’ Burggraaff explains. ‘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 ourselves to use these cameras for scientific purposes.’
New possibilities
Earlier calibration efforts were often hampered by a lack of access to the software or available information about the devices. For example, until recently it wasn’t possible to access data straight from the camera sensor— known as so-called RAW data — or to control several camera settings like focus or exposure. However, new versions of iOS and Android now allow both. ‘As part of SPECTACLE, we are developing a framework for both operating systems to make measurements using RAW data and process these on the phone. That simply was not possible a few years ago,’ Burggraaff says.
The next step
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. They will also continue to develop the iSPEX smartphone add-on to improve its ability to acquire water and air pollution measurements.
After a press release of the Optical Society - Calibration methods improve scientific research performed with smartphone cameras
Paper: O. Burggraaff, N. Schmidt, J. Zamorano, K. Pauly, S. Pascual, C. Tapia, E. Spyrakos, F. Snik, “Standardized spectral and radiometric calibration of consumer cameras,” Opt. Express, Vol. 27, Issue 14, pp. 19075-19101 (2019).
DOI: 110.1364/OE.27.019075
Both SPECTACLE and iSPEX are part of MONOCLE (Multiscale Observation Networks for Optical monitoring of Coastal waters, Lakes and Estuaries), a project funded by the European Commission aimed at creating sustainable solutions for measuring optical water quality.
For more information on MONOCLE, contact the project office at monocle@pml.ac.uk.