Gestalt Theory.- The Helmholtz Principle.- Estimating the Binomial Tail.- Alignments in Digital Images.- Maximal Meaningfulness and the Exclusion Principle.- Modes of a Histogram.- Vanishing Points.- Contrasted Boundaries.- Variational or Meaningful Boundaries?.- Clusters.- Binocular Grouping.- A Psychophysical Study of the Helmholtz Principle.- Back to the Gestalt Programme.- Other Theories, Discussion.