| xi | Intensity value of pixel i |
| h(x) | Histogram of the image I,x ∈ [0,L-1] |
| r | Image size in terms of pixel numbers |
| Tr (I) | Transformation function of image I |
| pj (xi; θj) | j-th probability density function with parameter set θj |
| μj | Mean of cluster j |
| ∑j | Variance of cluster j |
| within2 between2 |
Within-class variance, Between-class variance. |
| ω (T)i=1,2 | Probabilities of the two clusters separated by threshold T |
| f (x) | Image expressed with spatial term x, which refers to pixel location |
| λ (in GMAC) | Scalar that controls the balance between regularization and data |