Arc Finder edges. Contrast Threshold Modes Contrast Threshold Mode defines how contrast threshold is set. Contrast threshold is the level of sensitivity that is applied to the detection of edges in the input image. The contrast threshold can be either Adaptive, or Fixed. Adaptive thresholds set a sensitivity level based on image content. This provides flexibility to variations in image lighting conditions and contrast during the Search process. l Adaptive Low Sensitivity uses a low sensitivity, adaptive threshold for detecting edges. Adaptive Low Sensitivity detects strongly defined edges and eliminates noise, at the risk of losing significant edge segments.
l Adaptive Normal Sensitivity sets a default sensitivity threshold for detect- ing edges. l Adaptive High Sensitivity detects weaker edges, at the risk of adding noise. l Fixed Value sets an absolute value for sensitivity to contrast. A typical use of a fixed value is an application in which there is little variance in lighting conditions. o Higher values reduce sensitivity to contrast. This reduces noise and decreases the number of low-contrast edges detected. o Lower values increase sensitivity to contrast. This detects more edges, at the expense of adding more noise. This may generate false detections and/or slow the search process.
Maximum Angle Deviation Maximum Angle Deviation is the maximum allowable deviation in angle between the arc hypothesis and the arc found by the tool. The deviation is calculated between the tangent angle of the arc at points where the edge is matched to the arc. Positioning Level Positioning Level sets the effort level of the instance-positioning process. The range is from 10 (coarser positioning and lower execution time) to 100 (high-accuracy positioning of arcs). Subsampling Level This property sets the subsampling level used to detect edges that are used by the tool to gen- erate hypotheses. ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 396