Fast selection of greyvalues within a given grey intervall.
fast_threshold selects the pixels from the input image whose gray values g fulfill the following condition:
MinGrey <= g <= MaxGrey .To reduce procesing time, the selection is done in two steps: At first all pixels along rows with distances MinHeight are processed. In the next step the neighborhood (size MinHeight @x MinHeight) of all previously selected points are processed.
Image (input_object) |
image(-array) -> object : byte / direction / cyclic |
Image to be thresholded. |
Region (output_object) |
region(-array) -> object |
Regions with gray values lying in the specified interval. |
MinGrey (input_control) |
number -> real / integer |
Lower threshold for the gray values. | |
Default value: 128 | |
Suggested values: 0.0, 10.0, 30.0, 64.0, 128.0, 200.0, 220.0, 255.0 | |
Range of values: 0.0 <= MinGrey <= 255.0 (lin) | |
Minimum increment: 1 | |
Recommended increment: 5.0 |
MaxGrey (input_control) |
number -> real / integer |
Upper threshold for the gray values. | |
Default value: 255.0 | |
Suggested values: 0.0, 10.0, 30.0, 64.0, 128.0, 200.0, 220.0, 255.0 | |
Range of values: 0.0 <= MaxGrey <= 255.0 (lin) | |
Minimum increment: 1 | |
Recommended increment: 5.0 |
MinHeight (input_control) |
number -> integer |
Minimum height of objects to be extracted. | |
Default value: 20 | |
Suggested values: 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 100 | |
Range of values: 2 <= MinHeight <= 200 (lin) | |
Minimum increment: 1 | |
Recommended increment: 2 |
Let F be the area of the ouput region and height the height of Image. Then the runtime complexity is O(F + height / MinHeight).
fast_threshold returns TRUE if all parameters are correct. The behaviour 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.
histo_to_thresh, min_max__, sobel_amp, gauss__, reduce_domain, fill_interlace__
connection, dilation1, erosion1, opening, closing, count, shape_trans, skeleton
class_2dim__, hysteresis_threshold__, dyn_threshold__