Perform a hysteresis threshold operation on an image.
hysteresis_threshold performs a hysteresis threshold operation (introduced by Canny) on an image. All points in the input image Image having a gray value larger than or equal to High are immediately accepted (``secure'' points). Conversely, all points with gray values less than Low are immediately rejected. ``Potential'' points with gray values between both thresholds are accepted if they are connected to ``secure'' points by a path of ``potential'' points having a length of at most MaxLength points. This means that ``secure'' points influence their surroundings (hysteresis).
|
Image (input_object) |
image(-array) -> object : byte / uint2 |
| Input image. | |
|
RegionHysteresis (output_object) |
region(-array) -> object |
| Segmented region. | |
|
Low (input_control) |
integer -> integer |
| Lower threshold for the gray values. | |
| Default value: 30 | |
| Suggested values: 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100 | |
| Typical range of values: 0 <= Low <= 255 (lin) | |
| Minimum increment: 1 | |
|
Recommended increment: 5 | |
| Restriction: (0 < Low) && (Low < 255) | |
|
High (input_control) |
integer -> integer |
| Upper threshold for the gray values. | |
| Default value: 60 | |
| Suggested values: 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130 | |
| Typical range of values: 0 <= High <= 255 (lin) | |
| Minimum increment: 1 | |
|
Recommended increment: 5 | |
| Restriction: ((0 < High) && (High < 255)) && (High > Low) | |
|
MaxLength (input_control) |
integer -> integer |
| Maximum length of a path of ``potential'' points to reach a ``secure'' point. | |
| Default value: 10 | |
| Suggested values: 1, 2, 3, 5, 7, 10, 12, 14, 17, 20, 25, 30, 35, 40, 50 | |
| Typical range of values: 1 <= MaxLength | |
| Minimum increment: 1 | |
|
Recommended increment: 5 | |
| Restriction: MaxLength > 1 | |
hysteresis_threshold returns 2 (H_MSG_TRUE) if all parameters are correct. The behavior with respect to the input images and output regions can be determined by setting the values of the flags 'no_object_result', 'empty_region_result', and 'store_empty_region' with set_system. If necessary, an exception is raised.
hysteresis_threshold is reentrant and automatically parallelized (on tuple level).
dyn_threshold, threshold, class_2dim_sup, fast_threshold
edges_image, sobel_dir, background_seg
J. Canny, "Finding Edges and Lines in Images"; Report, AI-TR-720, M.I.T. Artificial Intelligence Lab., Cambridge, MA, 1983.
Foundation
