Multiscale fusion algorithms (wavelet or pyramid) can generally satisfy multisensory image fusion. However, those
algorithms are not ideal to fuse visible images and infrared images whose intensities appear inverted. Therefore, a novel
orientation-based fusion algorithm is proposed in this paper to address this problem. Specifically, a set of MxN Gabor
wavelet transforms (GWT) are performed with two input images (IA and IB). At each frequency band (b = 1, 2, ..., M),
the index of maximal GWT magnitude between two images is selected pixel by pixel; and then two index frequencies,
HA(b) and HB(b), are calculated as its index accumulation along N orientations, respectively. The final HA and HB are the
weighted summations through M bands, where the band weights (Wb) are given empirically. Eventually, the fused image
is computed as IF = (IA .* HA + IB .* HB)/( HA + HB), where '.*' denotes element-by-element product of two arrays. The
orientation-based fusion algorithm can be further varied by either keeping DC (direct current) or suppressing DC in
GWT. "Keeping DC" will produce a contrast-smooth image; while "suppressing DC" will result a sharpened fusion.
Color fusion is achieved by replacing the red channel of a color image with the fused image, which is suitable for poorly
illuminated color images. Not only are the fused images of visible and infrared images satisfied, but the fusions of other
image sets are also comparable to the results of multiscale fusion algorithms. The proposed algorithm can be applied to
multiple (more than two) image fusion.