Minutiae are major features of a friction ridge structure, and consist of ridge endings and bifurcations. Their location and direction marking is defined by EFS in a manner that is interoperable across different AFIS systems. Minutiae are a critical part of the Quick Minutiae Search and Detailed Markup profiles; accurate marking of all identifiable minutiae is a major factor in obtaining optimal search performance.

Mark all minutiae in an impression, including short ridges or minutiae near cores and deltas (this is a departure from traditional markup methods). If a receiving AFIS does not differentiate such minutiae, it will make the appropriate adjustments. Ridges less than twice as long as their width should be marked as dots rather than minutiae.

Corresponding ridge endings and bifurcations provide strong supporting evidence for a match between impressions. Because minutiae frequently appear to be ridge endings in one impression and bifurcation in another, even in clear images, it is not recommended that minutia type be used as a basis for exclusion.

Location and Direction

When identifying minutiae, the markup locations for bifurcations and ridge endings are equivalent: the location always goes in the center of a point where a ridge or valley splits to form a "Y" shape. The minutia direction, or theta angle, then points along the gap between the two ridge or vally branches of the "Y". Thus, for a bifurcation, the minutia’s location is where the ridge starts to split into two, and the minutia’s direction moves along the valley between the two branching ridges.

If an image were tonally reversed (light and dark areas switched), every minutia would be marked in the same way.

The ridge ending location corresponds with that used for the FBI’s Integrated Automated Fingerprint Identification System (IAFIS) and Next Generation Identification (NGI), as well as the INCITS 378, (ANSI/INCITS 2004) definition, but differs from some legacy vendor-specific approaches.

The EFS data specification differentiates between ridge endings and bifurcations; however, some AFIS vendors make no such distinction.

Handling Uncertainty

If you identify the general location of a minutia but cannot distinguish which type it is, mark the feature type as "unknown". In most unknown cases, the precise location will be unclear and a radius of uncertainty should be indicated. In these cases, the radius of uncertainty outlines an area that includes the location of the minutiae if it were a bifurcation, and the location of the minutiae if it were a ridge ending.

The angle of a minutia may be more difficult to determine when the direction of ridge flow is ambiguous, when the ridges are near the minutiae curve, or when the ridges come together at obtuse angles. In such cases, the angle of a bifurcation is determined by following each of the three ridges forming the bifurcation for a distance of about three ridge widths (1.93mm or 0.064"); the smallest of the three angles formed by the rays is bisected to indicate the minutiae direction. The angle of a ridge ending is determined equivalently, based on following the three valleys that form the ridge ending.

Mark all complex minutiae types as combinations of bifurcation/endings; for example, mark a crossover or trifurcation as two bifurcations located closely together. The figure to the right shows a trifurcation and a crossover, and their correct markup.

Minutiae should be marked even if there is some doubt about its presence; most vendor software will perform better if the feature is marked

Click on the center of the "Y" of a ridge ending or bifurcation, then drag to indicate the minutia’s direction. Repeat for every minutia you see in the image. To remove a particular minutia mark, select the Delete tool and then click on that mark.

This tool does not allow you to mark radius of uncertainty for a minutia, but an EFS-compliant workstation will.

Click the arrows to the image’s left and right to navigate to different minutiae exercises, and click Check My Answer to get feedback on your responses.