Hierarchical Fusion of Multi Spectral Face Images for Improved ... - IIIT

Since the visible and IR imaging devices usually have different spatial resolutions andviewpoints, face images may exhibit different pose and size. Before fusion, face imagesshould be normalized and aligned. Face region is first detected using the triangle basedface detection algorithm [10]. Preprocessing is then performed using affinetransformation, which also handles the rotation, translation and scaling.Let x , ) , x , ), and x , ) be the eyes and mouth coordinates respectively in the( 1 y1( 2 y2( 3 y3visible image and x ′,′), x ′ , ′ ), and x ′ , ′ ) be the corresponding coordinates in( 1 y1( 2 y2( 3 y3the IR face image. We calculate a transformation matrix TM to align the two detectedface images,−1⎡x1′x′2 x3′⎤⎡x1x2x3⎤TM =⎢⎥⎢⎥ ×⎢y1′y′2 y3′(26)y⎥1 y2y3⎣⎦⎢⎣111 ⎥⎦which gives⎡u1v1w1⎤TM = ⎢⎥(27)⎣u2v2w2⎦This transformation is generalized to the whole image,x = u ′ ′ +1x+ v1y w1y = u ′ ′ +2x+ v2y w2(28)Let I V and I IR be the preprocessed visible and IR face images. First, the pixel values of I Vand I IR are transformed in the range of (0, 1). Single level DWT is then applied on theseimages to obtain the detail and approximation wavelet bands for both the images. Let16