Lumidigm’s multispectral imaging technology works in extreme conditions, including rain. Conventional optical technologies are often unable to produce images in wet conditions because excess moisture obscures fingerprint ridges, resulting in images of puddles, not fingerprints. Multispectral fingerprint sensors capture high-quality images in this situation because the direct imaging process does not depend on a clean finger/sensor interface.

Wet conditions: two fingerprint technologies produce different results

The fingerprint images shown here illustrate this point. A finger was submerged in a pool of water and placed on two sensors. The conventional optical sensor was unable to capture a good image because the water interfered with the finger/sensor interface. The Lumidigm sensor was able to “see” the fingerprint and produce a high-quality image in this very wet real world condition.

Lumidigm’s “waterfall demo”, used to demonstrate the capabilities of its fingerprint products in wet conditions.

Multispectral imaging from Lumidigm is up to the challenge. But what is the challenge? How can a diverse user population affect fingerprint image quality and system performance?

Fingerprint images taken from an elderly woman. The Lumidigm sensor was able to collect a usable image.

There are several physiological differences that can affect performance. Many people, both young and adult, have small or fine fingerprint features that can be difficult to image. If the sensor cannot differentiate between these fine characteristics, system performance will suffer. Age is another physiological characteristic that can affect the ability of a sensor to collect a usable fingerprint image. One effect of aging is the loss of collagen in the skin; elderly fingers have soft fingerprint ridges that collapse into each other when the finger touches a surface. Because many sensor technologies depend on the quality of contact between the finger and the sensor to collect a good image, soft fingerprint ridges can be difficult to image.

Multispectral imaging from Lumidigm is relatively immune to these physiological differences because of its ability to collect unique fingerprint information from both the surface and the subsurface of the skin. If surface information is scarce for whatever reason, Lumidigm sensors can still gather enough relevant fingerprint information to produce a usable image.

There are behavioral differences across user populations that can also affect performance. People have different levels of experience with technology and biometrics and this affects how they approach the fingerprint sensor. For example, some people may tend to press hard and others, being more tentative, may barely touch the sensor at all. For technologies that depend on the quality of that touch, this can be a big problem. For a direct imaging system such as the Lumidigm sensor, this is no problem at all!

Lumidigm’s multispectral imaging technology has been proven in the field with large and diverse user populations. People of all ages and backgrounds use our sensors every day.

Past attempts to compensate for fingerprint sensors’ inability to image dry fingerprints have involved instructions to the user to properly condition their skin (“moist, but not too moist!”) before touching the sensor. However, multispectral imaging technology from Lumidigm captures high-quality images even when fingers are dry.

It’s hard to appreciate Lumidigm’s solution without first understanding why conventional technologies have so much trouble with dry fingers. Most optical sensors are configured to look for the presence or absence of total internal reflectance (TIR), which is the phenomenon whereby the interface between glass and air acts like a mirror at certain angles. The contact between the skin and the platen defeats the TIR, allowing those points of contact between the finger and the sensor to be imaged. Thus, those points of contact must be complete and unobscured to enable the conventional sensor to collect a fingerprint image. And with dry fingers, this is simply not the case! Establishing firm and complete contact with the sensor is very difficult with dry fingers. There is not enough moisture in the skin nor is the skin pliable enough to facilitate the contact necessary for TIR imaging.

Dry conditions: the conventional optical sensor could not capture a complete image because the skin was not moist or pliable enough to establish good contact with the sensor.

Lumidigm fingerprint sensors do not require perfect contact between the finger and the platen because they use multispectral imaging, a direct imaging technology. Rather than capturing information about the finger/sensor contact and creating an image from that, the Lumidigm sensor effectively takes a snapshot of the fingertip. It is in this way that Lumidigm sidesteps the problem of dry fingers in the real world.

A construction site is an interesting real world case. Construction workers work with their hands and have the cuts and calluses to prove it. Additionally, the construction site is dirty so workers may have grime on their hands when they approach a fingerprint sensor. Altogether, this real world scenario is a nightmare for system administrators whose conventional fingerprint sensors depend on quality contact between the finger and the platen.

Images of a construction worker’s fingerprint, collected with two different sensor technologies

Lumidigm’s multispectral fingerprint sensors work well in situations such as these for two important reasons. First, they are able to gather fingerprint information from beneath the surface of the skin. It is not a problem if the fingerprint ridges on the surface are marred by an injury or a callous because the subsurface information remains intact, and Lumidigm sensors can collect it. Second, Lumidigm sensors do not require perfect finger/sensor contact. If a user’s finger is dirty — an occupational hazard of a construction worker — the debris will prevent good clean contact between the finger and the sensor. This is a huge problem for a conventional optical sensor, but no problem at all for a multispectral imaging sensor.