Figure 1.

(${\mathit{A}}_{\mathit{0}}$) Initial image. (${\mathit{B}}_{\mathit{0}}$) Salt and pepper noise. (${\mathit{C}}_{\mathit{0}}$) Gaussian noise. (${\mathit{D}}_{\mathit{0}}$) Uniform noise. (${\mathit{A}}_{\mathit{1}}$–${\mathit{A}}_{\mathit{8}}$): Euclidean-distance-based fuzzy c-means clustering (FCM-EU), Euclidean-distance-based biogeography-based optimization (FCM-EU-B), Euclidean-distance-based firefly algorithm (FCM-EU-F), Euclidean-distance-based genetic algorithm (FCM-EU-GA), Mahalanobis-distance-based fuzzy c-means clustering (FCM-M), Mahalanobis-distance-based biogeography-based optimization (FCM-M-B), Mahalanobis-distance-based firefly algorithm (FCM-M-F), and Mahalanobis-distance-based genetic algorithm (FCM-M-GA), for (${\mathit{A}}_{\mathit{0}}$). Similar for (${\mathit{B}}_{\mathit{1}}$–${\mathit{B}}_{\mathit{8}}$), (${\mathit{C}}_{\mathit{1}}$–${\mathit{C}}_{\mathit{8}}$), and (${\mathit{D}}_{\mathit{1}}$–${\mathit{D}}_{\mathit{8}}$) and for (${\mathit{B}}_{\mathit{0}}$), (${\mathit{C}}_{\mathit{0}}$), and (${\mathit{D}}_{\mathit{0}}$), respectively.