ISODATA — three parameters the user must set.

• N — max number of clusters. Becomes the maximum possible number of classes.
• T — convergence threshold. The % of pixels whose class values must stay unchanged between iterations to declare convergence (e.g., 95%, 98%).

• M — max iterations. Safety limit so the algorithm halts even if T is never reached.

• Rule of thumb: if ISODATA returns far fewer clusters than N, your data doesn’t support that many; if it maxes out N, bump the parameter up.