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General Description of Fingerprints
The general classification of fingerprints used today came from the work of Sir Edward Henry, who published his book, Classification and Use of Fingerprints , in 1900. This work forms the basis for modern-day fingerprint forensics. Fingerprints are identified by both macro and micro features. The macro features of a fingerprint include:
The micro features of a fingerprint are made up of minutia points. Minutia points are classified by:
Let's examine the macro features, then the micro features of a fingerprint.
Macro Fingerprint Features
Macro fingerprint features are, as the name implies, large in size (Figure 5-1). In general, a feature is considered macro if it can be seen unaided by the human eye. The most visible macro feature seen is the ridge pattern. Others can be seen if the print has good ridge/valley definition, the lighting is good, and your eyesight is excellent !
Figure 5-1. Ridge patterns.
Ridge pattern area
The ridge pattern area is the area in the print where all the macro features are found (Figure 5-2). It is normally defined by diverging ridge flows that form a delta.
Figure 5-2. Ridge pattern area.
The core point is found at the center of the finger image (Figure 5-3). It may or may not correspond to the center of the ridge pattern area. It is used as a reference point for measuring other minutia and also during classification. Classification is the organizing of prints based on their ridge pattern.
Figure 5-3. Core point.
"The Delta is the point on the first ridge bifurcation , abrupt ending ridge, meeting of two ridges, dot, fragmentary ridge, or any point upon a ridge at or nearest the center of divergence of two type lines, located at or directly in front of their point of divergence . It is a definite fixed point used to facilitate ridge counting and tracing."  In Figure 5-4, the delta point has been magnified.
Figure 5-4. Delta point.
Type lines are the two parallel innermost ridges that define the ridge pattern area. In Figure 5-5, the type lines are the two slightly darker ridge lines in the enlarged section.
Figure 5-5. Type lines.
Ridge count is the number of ridges that intersect a line drawn from a delta to the core. There could be more than one ridge count for each finger image. For each delta in the finger image, there will be a corresponding ridge count between it and the core. In Figure 5-6, the ridge count from the delta to the core is 12 ridges.
Figure 5-6. Ridge count.
Micro Fingerprint Features
As the name implies, micro fingerprint features cannot be seen unaided by the human eye. A number of the current fingerprint scanners on the market now have a high enough resolution that pores can be counted. What follows is a description of the minutia that make up the micro features:
There are a number of different types of minutia; the common ones are:
A ridge ending is a gap in a ridge or a point where a ridge suddenly stops (Figure 5-7).
Figure 5-7. Ridge ending.
A ridge bifurcation occurs when a ridge splits into two or more new ridges (Figure 5-8).
Figure 5-8. Ridge bifurcation.
A ridge divergence occurs when two ridges running parallel suddenly diverge in opposite directions. In Figure 5-9, the two ridges diverge at the point where another ridge has a bifurcation.
Figure 5-9. Ridge divergence.
Dot or island
A dot or island occurs when a ridge is short enough to be perceived as a single point (dot) or straight line (island). In Figure 5-10, we can see a group of three dots or islands.
Figure 5-10. Dot or island.
Enclosure or lake
An enclosure (lake) minutia occurs when a ridge bifurcates and then rejoins itself. This then leaves a valley surrounded by the rejoined ridge. In Figure 5-11, the ridge has created two enclosures.
Figure 5-11. Enclosure or lake.
A short ridge is a ridge of short length, but not so short as to be considered an island or dot. In Figure 5-12, you can see two short ridges and two dots. Notice the short ridges have more of a linear look to them. The dots have more of a circular look to them.
Figure 5-12. Short ridge.
Orientation refers to the general direction in which a minutia feature appears to be moving. In Figure 5-13, both scaled areas contain bifurcations, but their orientation is different. The bifurcation in the left-hand enlarged area would have a general slope of approximately 1. The bifurcation in the right-hand enlarged area would have a general slope of -1.
Figure 5-13. Orientation.
Spatial frequency can be viewed as the density of ridges around a given minutia point. In Figure 5-14, the spatial frequency is higher around the island at the top right than the bifurcation at the middle left.
Figure 5-14. Spatial frequency.
Curvature is the rate of change of a ridge's direction. In the above left enlargement in Figure 5-15, the rate of change is lower, as the ridge curves are flatter. In the bottom right enlargement in Figure 5-15, the rate of change is higher, as the ridge curves are tighter.
Figure 5-15. Curvature.
Position refers to the relative location of the minutia. References are normally made using a Euclidian grid, and having the origin either at the core point or at a delta. In Figure 5-16, the origin has been placed at the core point. The numbers at the end of each axis are at their maximum value. In our example, you can find a bifurcation at (1,-1) and a group of dots at (-1,1.5)
Figure 5-16. Position.
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