Biometrics can be used to identify people using a range of criteria. One category of biometrics is behavioural, meaning the actions performed by a particular person, such as keystrokes on a keyboard or voice recognition. The other category is physiological criteria, such as iris scanning, facial recognition or fingerprints. The information obtained can be used to track everything from criminal behaviour to consumer behaviour.
Image sensors, which are often used to track physiological biometrics, have been undergoing some changes. Recent advancements in the technology have led to the increased prevalence of CMOS imaging sensors. These types of sensors offer a range of benefits but also drawbacks when compared to other types of technology.
Understanding CMOS Image Sensors versus CCD Image Sensors
Both the charge-coupled device, or CCD, and the complementary metal oxide semiconductor, or CMOS, have the capacity to take light and convert it into an electric charge which is then processed into electronic signals. The way they each go about this processes, however, is different.
The CCD sensor works by transferring the pixels through a limited number of nodules which are then converted to a specific voltage, buffered, and transferred off the chip. Conversely, the CMOS works by having an individual charge to voltage conversion ratio for each pixel.
CMOS systems is noted for reducing the light capacity, which in the past led to lower quality images. Although both types were invented around the 1960s and 1970s, it was not until the 1990s that the technology was developed that allowed CMOS sensors to compete with CCD.
For this reason, the majority of the imaging sensors have historically been based on CCD technology. In recent years, CMOS technology has improvement dramatically, fuelled by consumer imaging applications in devices like cell phones and webcams, and has advanced to the point where it could reasonably compete with CCD in terms of quality in biometrics.
The main advantage of CMOS technology is speed, which allows biometric manufacturers to develop high accuracy systems (using high-resolution CMOS image sensors) with an acceptable processing speed. This results in fast and very accurate identification using finger/palm print scanners for instance.
The Use of Image Sensors in Biometrics
Image sensors have a variety of uses in biometrics. Some of the more popular uses involve palm and fingerprint scanners used as identification for border control, identification at police stations, offices issuing passports etc. These sensors are in general high-resolution sensors (> 5 MP) to capture the biometry data with the highest accuracy.
Advantages of CMOS in Imaging Sensors
Since machines are critical for the use of biometrics with imaging sensors, the key parameters that would be examined are speed and noise. Speaking generally, CCD sensors tend to require higher bandwidth, and thus it is much easier to create a CMOS imaging sensor that does not produce as much noise as the CCD. CMOS also typically operate faster than CCD sensors.
Previously, CCD sensors had the advantage of superior overall quality due to the light limitations of the CMOS, but the recent advancements in the technology of CMOS sensors now allow them to compete closer to the level of the CCD imaging sensors. CMOS technology also tends to use less power than CCD technology.
Digital camera technology continues to develop, contributing to the improvement of biometric techniques. CMOS image sensors have improved, and now can provide the quality that was previously seen only with the CCD image sensors. CMOS sensors now can provide those working in biometrics with a range of advantages, and those in the market for an image sensor should carefully consider the options available to see what would fit best with their particular machines.
CMOSIS is a supplier of advanced off the shelf, customised and full custom CMOS image sensors developed by multi disciplinary team of image sensor experts. They offers CMOS image sensor products optimized for specific application fields.
These products feature high-performance pixel architectures, high frame rates, on-chip ADC, high dynamic range operation modes and high-speed digital interfaces. They are used in 3D imaging, automotive, motion anaysis, scientific and security fields.
This information has been sourced, reviewed and adapted from materials provided by CMOSIS.
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