SAFR measures the difference between a face image and the stored identity image by a difference measure known as "Identity Recognition". The value of Identity Recognition can range from 0 to about 1.3. Values of 0.54 or lower represents a certain match and values above 1.0 are interpreted as different faces.
SAFR has 2 configurable settings that define the acceptable difference between a reference image and the event face image. These are defined as follows:
- Identity Recognition Threshold - The largest difference between a face image and a stored identity at which SAFR will report a 100% confidence match. As noted above, a value of 0.54 or lower represents a certain match. This is the default value for SAFR and should generally not be modified.
- Proximity Threshold Allowance - A boost value to the Identity Recognition Threshold. The sum of Identity Recognition Threshold and Proximity Threshold Allowance is used as largest difference between a face image and a stored identity at which SAFR will report a reduced confidence match.
As noted above, SAFR interprets the value of Identity Recognition Threshold as a certain match. Any face that is within 0.54 or lower will be reported as a match. SAFR uses Proximity Threshold Allowance to report possible matches. Is does this by reporting a match with a percentage confidence. Any value that is between the Identity Recognition Threshold (e.g. 0.54) and the Proximity Threshold Allowance boosted value (e.g. 0.92) will be reported as a probable match using a percentage scale as follows:
Proximity Threshold Allowance Boost Confidence Table
Identity Recognition Threshold | Proximity Threshold Allowance | Combined Value | Confidence | Interpretation |
0.54 | 0 | 0.54 or less | 100% | Certain match (values > 100% are possible indicating even greater certainty) |
0.54 | 0.14 | 0.68 | 93% | Close match but not certain enough to unlock the door |
0.54 | 0.3 | 0.84 | 86% | Possible match with low confidence |
0.54 | 0.38 | 0.92 | 82% | Similar face with no confidence of match |
0.54 | 0.51 | 1.05 | 79% or less | Different face |
The confidence match is overlaid on the video or images just below the face (alongside the name) and it is also reported in the SAFR Events returned thru REST APIs as the field "confidence".
Typical use of Proximity Threshold Allowance
- Watchlist monitoring - If you wish to have confidence reported in the user interface, it is generally recommended to set the Proximity Threshold Allowance to 0.38. With this value SAFR will begin to report faces that are 82% confidence or greater. You can adjust the value of Proximity Threshold Allowance to limit matches to higher or lower confidence. This is typical for a watchlist scenario where you wish to see possible matches. Operators should be educated to understand the interpretation provided in above table and use that information accordingly with possible matched individuals.
- Secure Access - If you do not wish to have confidence reported, then set Proximity Threshold Allowance to 0. In this case only certain matches are reported. This is typically used typically in Secure Access mode where only certain match is desired.
- User verification - In some cases, you wish to validate a user based on a document they present such as a photo ID. While a 100% confidence is desired, this may not always be possible given age difference between the photo ID and the subject or condition of the ID. In these cases, it may be acceptable to use the confidence value returned by SAFR REST APIs to gauge a close match. For example, a value of 93% confidence could be considered sufficiently close to authorize registration.