**2.1. Influence of light on iris acquisition**

The light we perceive around us is an electromagnetic waving in the visible spectrum. Each of these waves has its own wavelength. We see the colors as different wavelengths of the visible spectrum, but the eye responds to other wavelengths as well [5]:


• 400–1400 nm: passes through the lens on the retina. For visible light in the range of 400– 700 nm, the eye reacts within 0.25 s.

First, an *iris* (curve boundary) is *located* in the image of the eye. The iris is located with the

(*r*) <sup>∗</sup> \_\_<sup>∂</sup> <sup>∂</sup>*<sup>r</sup>* ∮ *r*,*x*<sup>0</sup> ,*y*0

and the operator searches for the maximum in the blurred partial derivative of the image with

edge detector and returns the maximum if the candidate circle shares the pupil center and the

The next step is *locating* the *lid*. The position of the lower and upper eyelids is determined by the same procedure as the iris itself. The part of the previous formula (Eq. (1)) used to detect the contour is replaced by a circular arc, the parameters being set according to standard

(*r*) is the Gaussian smoothing function according to *σ*, *I*(*x*,*y*) is the raw input image,

*I*(*x*, *y*) \_\_\_\_\_

<sup>2</sup>*<sup>r</sup> ds*<sup>|</sup> (1)

http://dx.doi.org/10.5772/intechopen.76026

Recognition of Eye Characteristics

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, *<sup>y</sup>*0). The operator is essentially a circular

,*y*0) |*Gσ*

following operator:

where *G<sup>σ</sup>*

max(*r*,*x*<sup>0</sup>

respect to the radius *r* and the center coordinates (*x*<sup>0</sup>

**Figure 3.** Identification process of Daugman's algorithm.

**Figure 4.** Examples of localized irises.

radius. Examples of localized irises are shown in **Figure 4**.

• More than 1400nm: it absorbs the cornea, causing strong tearing and increasing temperature.

Under the visible light, we can observe the visible layers, especially on the iris. It reveals less textural information than infrared (IR) light; melanin usually absorbs visible light.

By contrast, infrared (IR) light melanin predominantly reflects and is preferred for iris recognition because it is more user-friendly; it does not irritate and does not cause the unpleasant feelings associated with eye illumination.

There are four basic schemes for iris recognition:

