Definiens Developer 7 - PCI Geomatics

Definiens Developer 7 - Reference Book3 Algorithms ReferenceTipProduce Image Objects that Suit the Purpose (2)Use as much color criterion as possible while keeping the shape criterion as high as necessaryto produce image objects of the best border smoothness and compactness. The reason forthis is that a high degree of shape criterion works at the cost of spectral homogeneity.However, the spectral information is, at the end, the primary information contained in imagedata. Using too much shape criterion can therefore reduce the quality of segmentationresults.In addition to spectral information the object homogeneity is optimized with regard tothe object shape. The shape criterion is composed of two parameters:SmoothnessThe smoothness criterion is used to optimize image objects with regard to smoothnessof borders. To give an example, the smoothness criterion should be used when workingon very heterogeneous data to inhibit the objects from having frayed borders, whilemaintaining the ability to produce non-compact objects.CompactnessThe compactness criterion is used to optimize image objects with regard tocompactness. This criterion should be used when different image objects which arerather compact, but are separated from non-compact objects only by a relatively weakspectral contrast.Use the slider bar to adjust the amount of Compactness and Smoothness to be usedfor the segmentation.NoteIt is important to notice that the two shape criteria are not antagonistic. This meansthat an object optimized for compactness might very well have smooth borders.Which criterion to favor depends on the actual task.3.2.5 Spectral Difference SegmentationMerge neighboring objects according to their mean layer intensity values. Neighboringimage objects are merged if the difference between their layer mean intensities is belowthe value given by the maximum spectral difference.spectral differencesegmentationThis algorithm is designed to refine existing segmentation results, by merging spectrallysimilar image objects produced by previous segmentations.NoteThis algorithm cannot be used to create new image object levels based on the pixellevel domain.Level NameThe Level name defines the name for the new image object level.24