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**Mean, standard deviation, variance — worked example (water class, 3 pixels, 2 bands).** Pixels: **(24, 3), (26, 5), (28, 10)**. Band 1 values: 24, 26, 28. Band 2 values: 3, 5, 10. $$ \bar{Q}_1 = \frac{24 + 26 + 28}{3} = 26 \qquad \bar{Q}_2 = \frac{3 + 5 + 10}{3} = 6 $$ **Standard deviation formula** (k pixels): $$ S_Q \;=\; \sqrt{\frac{\sum_{i=1}^{k} (Q_i - \bar{Q})^2}{k-1}} $$ - Band 1: `S_Q₁ = 2` - Band 2: `S_Q₂ = 3.6` **Variance = std²**: Band 1 = 4; Band 2 = 12.96.

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