Minimum Distance (1) — the formula.

For a pixel with measurement vector V and class m mean vector B_m:

\[D_{\text{ist}}(\text{class}_m) \;=\; \sqrt{\sum_{k=1}^{n} (B_{m,k} - V_k)^2}\]

• Euclidean distance across all n bands.
• The pixel is assigned to the class whose distance is smallest (closest mean).

Source: ERDAS Field Guide 2002 p. 232.