“…The expression for t Hot (g | r p ) in Eq. (16), which requires the knowledge of the mean vectors and covariance matrix under the two hypotheses, is the socalled Hotelling observer [1,7,15,34,35] and is a linear function of g. As pointed out in [36], the Hotelling observer is still analytically tractable in realistic cases (for example, when the background can be described by a stationary random process), whereas computing the likelihood ratio in practical cases is, in general, a difficult problem. The derivation above shows that, if the data are normally distributed, the Hotelling observer is equivalent to the likelihood ratio, in the sense that they differ by an additive or positive multiplicative constant.…”