Human Face Recognition

Biometric Systems

Biometric systems:

The basic block diagram of a biometric system


The basic block diagram of a biometric system

The diagram on right shows a simple block diagram of a biometric system. When such a system is networked together with telecommunications technology, biometric systems become telebiometric systems. The main operations a system can perform are enrollment and test. During the enrollment, biometric information from an individual is stored. During the test, biometric information is detected and compared with the stored information. Note that it is crucial that storage and retrieval of such systems themselves be secure if the biometric system is be robust. The first block (sensor) is the interface between the real world and our system; it has to acquire all the necessary data. Most of the times it is an image acquisition system, but it can change according to the characteristics desired. The second block performs all the necessary pre-processing: it has to remove artifacts from the sensor, to enhance the input (e.g. removing background noise), to use some kind of normalisation, etc. In the third block features needed are extracted. This step is an important step as the correct features need to be extracted and the optimal way. A vector of numbers or an image with particular properties is used to create a template. A template is a synthesis of all the characteristics extracted from the source, in the optimal size to allow for adequate identifiability.

                   If enrollment is being performed the template is simply stored somewhere (on a card or within a database or both). If a matching phase is being performed, the obtained template is passed to a matcher that compares it with other existing templates, estimating the distance between them using any algorithm (e.g. Hamming distance). The matching programme will analyse the template with the input. This will then be output for any specified use or purpose (e.g. entrance in a restricted area).


                    A biometric system can provide the following two functions [3]:

  • Verification A pre-stored template is matched against a sample directly, e.g a card or known database entry.
  • Identification Identifying from all the templates which one is the closest match to the input sample.

Performance measurement

  • False Accept Rate (FAR) or False Match Rate (FMR):

          The probability that the system incorrectly declares a successful match between the input pattern and a non-matching pattern in the database. It measures the percent of invalid matches. These systems are critical since they are commonly used to forbid certain actions by disallowed people.

  • False Reject Rate (FRR) or False Non-Match Rate (FNMR):

           The probability that the system incorrectly declares failure of match between the input pattern and the matching template in the database. It measures the percent of valid inputs being rejected.

  • Receiver (or relative) Operating Characteristic (ROC):

       In general, the matching algorithm performs a decision using some parameters (e.g. a threshold). In biometric systems the FAR and FRR can typically be traded off against each other by changing those parameters. The ROC plot is obtained by graphing the values of FAR and FRR, changing the variables implicitly. A common variation is the Detection error trade-off (DET), which is obtained using normal deviate scales on both axes. This more linear graph illuminates the differences for higher performances (rarer errors).


  • Equal Error Rate (EER):

              The rate at which both accept and reject errors are equal. ROC or DET plotting is used because how FAR and FRR can be changed, is shown clearly. When quick comparison of two systems is required, the ERR is commonly used. Obtained from the ROC plot by taking the point where FAR and FRR have the same value. The lower the EER, the more accurate the system is considered to be.


  • Failure To Enroll Rate (FTE or FER):

               The percentage of data input is considered invalid and fails to input into the system. Failure to enroll happens when the data obtained by the sensor are considered invalid or of poor quality.



  • Failure to Capture Rate (FTC):

    Within automatic systems, the probability that the system fails to detect a biometric characteristic when presented correctly.



  • Template capacity:

The maximum number of sets of data which can be input in to the   system.



Want To Know more with

Video ???

Contact for more learning: webmaster@freehost7com





The contents of this webpage are copyrighted  2008
 All Rights Reserved.