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 represent are interpreted as certain matches, while 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 image 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 usually shouldn't be changed.
- Proximity Threshold Allowance - A boost value that is added to the Identity Recognition Threshold. The sum of Identity Recognition Threshold and Proximity Threshold Allowance is used as the largest difference between a face image and a stored identity image at which SAFR will report a reduced confidence match.
SAFR uses Proximity Threshold Allowance to report possible matches. It 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:
|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 in Secure Access scenarios.|
|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%||Different faces. |
The confidence match is overlaid on the videos or images just below the face (alongside the name) and is also reported in the SAFR Events returned through REST APIs in the confidence field.
Typical Uses of Proximity Threshold Allowance
Proximity Threshold Allowance is frequently used in the following scenarios:
- Watchlist monitoring - If you wish to have confidence reported in the user interface, it's generally recommended you 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 confidences, as desired. This is typical for a watchlist scenario where you wish to see possible matches. Operators should be educated so they understand the table above and can 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 in Secure Access video processing mode where only certain matches are desired.
- User verification - In some cases, you may 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 because of the poor condition of the photo ID or because of the age difference between the photo ID and the subject. In these cases, it may be acceptable to use the confidence value returned by SAFR to gauge a close match. For example, a value of 93% confidence could be considered sufficiently close to authorize registration.