Although smartphones and other consumer cameras are increasingly used for scientific applications, it is difficult to compare and combine data from different devices. A new easy-to-use standardized method enables almost anyone to calibrate these cameras without any equipment, helping hobbyists, science students, and professional scientists obtain useful data using any consumer camera.
The low cost of consumer grade cameras makes them an ideal choice for projects involving large-scale deployment, autonomous monitoring, or citizen science, "said Olivier Burggraaff, a research team at Leiden University in the Netherlands responsible for developing calibration methods. Our standardized calibration method will make it easier for anyone to use consumer cameras to detect aerosol particles in the air and measure pollution
In the Optical Society (OSA) journal Optics Express, a multi institutional research team reported their new standardized calibration method and database, called SPECTACLE (Standardized Photographic Equipment Calibration Techniques and Catalog), which can be used for cameras on smartphones, digital single lens reflex cameras, and drones. This database allows users to upload calibration data from their cameras for others to use.
SPECTACLE includes many DIY methods, and we have found that these methods provide results comparable to professional methods that require laboratory equipment, "Burggraaff said.
Improving Citizen Science
The development of standardized calibration methods was to meet the needs of Burggraaff and his Leiden University. Colleagues are developing citizen science methods to measure optical water quality, using smartphone accessory iSPEX (Spectropolarimeter from Planetary Exploration), which they initially developed for measuring air pollution. This add-on allows smartphone cameras to measure additional optical information, such as hyperspectral and polarization data. SPECTACLE and iSPEX are part of MONOCLE (Multi scale Observation Network for Optical Monitoring of Coastal Waters, Lakes, and Estuaries), a project funded by the European Commission aimed at creating sustainable optical water quality measurement solutions.
We need to have a good understanding of using smartphone cameras to measure water quality, as each manufacturer and device has its own characteristics, "Burggraaff said. SPECTACLE brings together many existing calibration methods and applies them to consumer cameras, which will make it easier for other developers and us to use these cameras for scientific purposes. ”
Although calibration methods for consumer cameras have been developed previously, these efforts are often hindered by a lack of access to software or available information about the device. For example, data can only be accessed directly from camera sensors until recently - known as RAW data - or to control many camera settings such as focus or exposure. However, both the new versions of iOS and Android allow for these two versions.
As part of SPECTACLE, we are developing a framework for two operating systems to measure and process RAW data on mobile phones, which was not possible a few years ago, "Burggraaff said.
DIY and laboratory methods
To test the new calibration method, researchers compared it with established methods using several cameras. For example, they found that the DIY method used to measure how a lens distributes light on a sensor (known as planar protection) matched 5% of the results from the standard method that requires an integrating sphere in laboratory settings. DIY methods include sticking stickers on the camera and capturing images of the sun or computer screen.
They also tested the spectral response curve of a smartphone camera with iSPEX and were able to obtain results within 4% of professional measurement methods, which require expensive and difficult to operate monochromators. Calibrating a single camera with a monochromator may take half a day, but the DIY method only requires taking a photo of a printed paper in sunlight.
We tested many cameras and found interesting differences and similarities between them, "Burggraaff said. For example, the response of a camera to light of different wavelengths, known as the spectral response curve, is very similar in most cameras, with only a few devices displaying ways that may affect the camera's perception and reproduction of color, even when accurately imaged. The same scene“
The researchers plan to apply the SPECTACLE method to a larger number of cameras to fill the database and gain a broader understanding of camera properties. This will be done by researchers and anyone who wants to upload calibration data to the database. They are still developing iSPEX smartphone accessories to enhance their ability to obtain water and air pollution measurements. This involves advancing its physical design and algorithms for retrieving scientific results from its data, while using the SPECTACLE method and database to combine data from different smartphones.