Locator sections of the object contour, such as shown in the "checkerboard back- ground" of the following example. Contrast Polarity - Local Changes in Polarity Contrast Threshold Contrast Threshold sets the minimum contrast needed for an edge to be detected in the input image. The threshold value expresses as the step in grey-level values required to detect contours. This threshold can be set to Low, Normal, High, or a fixed value. l Higher values reduce sensitivity to contrast. This reduces noise and the amount of low-contrast edges. l Lower values increase sensitivity and add a greater amount of edge at the expense of adding more noise.
This may generate false detections and/or slow down the search process. Contrast threshold is the level of sensitivity that is applied to the detection of contours 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 variations in contrast during the Search process. Adaptive Low Sensitivity Sets a low sensitivity, adaptive threshold for detecting contours. Adaptive Low Sensitivity detects strongly defined contours and eliminates noise, at the risk of losing significant contour segments.
Adaptive Normal Sensitivity Sets a default sensitivity threshold for detecting contours. ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 565