Fast selection of grayvalues within a given gray intervall.
::fast_threshold selects the pixels from the input image whose gray values g fulfill the following condition:
MinGray <= g <= MaxGray .
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) -> Hobject: HImage(Array) ( byte / direction / cyclic ) |
| Image to be thresholded. | |
|
Region (output_object) |
region(-array) -> Hobject * : HRegion(Array) |
| Regions with gray values lying in the specified interval. | |
|
MinGray (input_control) |
number -> HTuple.double / long |
| 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 | |
| Typical range of values: 0.0 <= MinGray <= 255.0 (lin) | |
| Minimum increment: 1 | |
|
Recommended increment: 5.0 | |
|
MaxGray (input_control) |
number -> HTuple.double / long |
| 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 | |
| Typical range of values: 0.0 <= MaxGray <= 255.0 (lin) | |
| Minimum increment: 1 | |
|
Recommended increment: 5.0 | |
|
MinHeight (input_control) |
number -> HTuple.long |
| Minimum height of objects to be extracted. | |
| Default value: 20 | |
| Suggested values: 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 100 | |
| Typical range of values: 2 <= MinHeight <= 200 (lin) | |
| Minimum increment: 1 | |
|
Recommended increment: 2 | |
Let A be the area of the ouput region and height the height of Image. Then the runtime complexity is O(A + height / MinHeight).
::fast_threshold returns 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.
::histo_to_thresh, ::min_max_gray, ::sobel_amp, ::gauss_image, ::reduce_domain, ::fill_interlace
::connection, ::dilation1, ::erosion1, ::opening, ::closing, ::rank_region, ::shape_trans, ::skeleton
::class_2dim_sup, ::hysteresis_threshold, ::dyn_threshold
Region processing
