Region of interest (ROI) extraction

The key issue to implement periocular region based biometric authentication system is to extract potential region of interest. The general approach (Park et al. 2009, 2011) is to use the coordinate of iris center as a reference point to extract periocular region of interest. In the proposed study, for the FERET database, same strategy (use of iris center) is implemented to extract periocular region of interest. The coordinates of iris center of images in FERET dataset is provided in its metadata. Considering the center of iris as center of periocular region of interest, a rectangular periocular region of 64 × 64 size is extracted from the face images for both left and right eye respectively.

Even though the above method is widely used in periocular literature, it does not work well if the eyes of the subjects are fully or partially closed. Hence an algorithm suggested by Liu et al. (2017) is used for the extraction of ROI from images of UBIPr and Ethnic Ocular datasets. This algorithm considers the canthus points as reference points (Fig. 4). The coordinates of canthus points of the images in UBIPr dataset is provided in its metadata but it was not provided in the metadata of ethnic ocular dataset. Hence, these points were extracted manually from the images in ethnic ocular dataset.

Illustration of medial/inner and lateral/outer canthus point

The algorithm is summarized in Algorithm 1.

Input:x1,y1 are the coordinate for medial canthus points and x2,y2 are the coordinate for lateral canthus points.

Output: Rectangular region of interest

Step 1: Calculate Euclidean distance between medial and lateral canthus points

Step 2 Compute Lp=Lpx,Lpy, midpoint of the line which connects medial and lateral canthus points.

Step 3: Compute the top left corner point x3,y3 and bottom right corner x4,y4 of rectangular ROI

Where a and b are constants whose values are chosen to cover the required periocular region

Step 4 Use the calculated points x3,y3 and x4,y4 to extract rectangular ROI.