... yields−xσ 2 e−x 2 /2 2 ≡cos ϕ + 2 xλsin ϕe−x 2 /2 2 . (6)With ϕ=−π/ 2and = 2 σ 2 , Gσ(x) will be the first or-der approximation of hσ ,2 σ 2 ,θ1,−π /2 (x,0).Thereforeit ... derivative of Gaussian.N. Chaji and H. Ghassemian 5Input imagehσ ,2 σ 2 ,θ1,−π /2 (x, y) hσ ,2 σ 2 ,θ 2 ,−π /2 (x, y) hσ ,2 σ 2 ,θNθ,−π /2 (x, y)ejθ1ejθ 2 ejθNθ·········ΣGradient ... ThresholdGoat 1 .2 0.9 0.43 2. 0 0.1 0.35Hyena1 .2 0.9 0.64 2. 0 0.1 0.56Gnu1 .2 0.9 0.47 2. 4 0.1 0.36Zebra1 .2 0.4 0.43 1.6 0.1 0.19Tiger1 .2 0.9 0.46 1.6 0.1 0 .23 Texture 2. 4 0.9 0.51 1 .2 0.1 0.19map...