Definiens Developer 7 - PCI Geomatics

Definiens Developer 7 - Reference Book3 Algorithms ReferencePrecondition: Thematic layers must be available.3.2.3 Contrast Split SegmentationUse the contrast split segmentation algorithm to segment an image or an imageobject into dark and bright regions.The contrast split algorithm segments an image (or image object) based on a thresholdthat maximizes the contrast between the resulting bright objects (consisting of pixelswith pixel values above threshold) and dark objects (consisting of pixels with pixelvalues below the threshold).The algorithm evaluates the optimal threshold separately for each image object in theimage object domain. If the pixel level is selected in the image object domain, thealgorithm first executes a chessboard segmentation, and then performs the split on eachsquare.contrast splitsegmentationThe algorithm achieves the optimization by considering different pixel values aspotential thresholds. The test thresholds range from the minimum threshold to themaximum threshold, with intermediate values chosen according to the step size andstepping type parameter. If a test threshold satisfies the minimum dark area andminimum bright area criterion, the contrast between bright and dark objects isevaluated. The test threshold causing the largest contrast is chosen as best thresholdand used for splitting.Chessboard Tile SizeAvailable only if pixel level is selected in the Image Object Domain. Enter thechessboard tile size.Default: 1000ChessboardSegmentation on page 15Level NameSelect or enter the level that will contain the results of the segmentation.Available only if the pixel level is in the image object domain.Minimum ThresholdEnter the minimum gray value that will be considered for splitting.The algorithm will calculate the threshold for gray values from the Scan Start value tothe Scan Stop value.Default: 0Maximum ThresholdEnter the maximum gray value that will be considered for splitting.The algorithm will calculate the threshold for gray values from the Scan Start value tothe Scan Stop value.Default: 255Step SizeEnter the step size by which the threshold will increase from the Minimum threshold tothe Maximum threshold. The value will either be added to the threshold or multipliedby the threshold, according to the selection in the Stepping type field.18