Operator Reference
dual_rank (Operator)
dual_rank — Opening, Median and Closing with circle or rectangle mask.
Signature
Description
The operator dual_rank carries out a non-linear
transformation of the gray values of all input images
(Image). Circles or squares can be used as structuring
elements. The operator dual_rank effects two
consecutive calls of rank_image. At the first call the
range gray value is calculated with the indicated range
(ModePercent). The result of this calculation is the
input of a further call of rank_image, this time using the
range value 100-ModePercent.
When filtering different parameters for border treatment
(Margin) can be chosen:
- gray value
Pixels outside of the image border are assumed to be constant (with the indicated gray value).
- 'continued'
Continuation of the gray values at the image border.
- 'cyclic'
Cyclic continuation at the image borders.
- 'mirrored'
Reflection of pixels at the image borders.
A range filtering is calculated according to the following scheme:
The indicated mask is put over the image to be filtered in such a
way that the center of the mask touches all pixels once. For each
of these pixels all neighboring pixels covered by the mask are
sorted in an ascending sequence corresponding to their gray values.
Each sorted sequence of gray values contains the same number of gray
values like the mask has image points. The n-th highest element, (=
ModePercent, rank values between 0...100 in
percent) is selected and set as result gray value in the
corresponding result image.
If ModePercent is 0, then the operator equals to the
gray value opening (gray_opening). If
ModePercent is 50, the operator results in the median
filter, which is applied twice (median_image). The
ModePercent 100 in dual_rank means that it
calculates the gray value closing (gray_closing).
Choosing parameter values inside this range results in a smooth
transformation of these operators.
For an explanation of the concept of smoothing filters see the introduction of chapter Filters / Smoothing.
Attention
Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.
Execution Information
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Automatically parallelized on tuple level.
- Automatically parallelized on channel level.
- Automatically parallelized on domain level.
Parameters
Image (input_object) (multichannel-)image(-array) → object (byte / int2 / uint2 / int4 / real)
Image to be filtered.
ImageRank (output_object) multichannel-image(-array) → object (byte / int2 / uint2 / int4 / real)
Filtered Image.
MaskType (input_control) string → (string)
Shape of the mask.
Default: 'circle'
List of values: 'circle', 'square'
Radius (input_control) integer → (integer)
Radius of the filter mask.
Default: 1
Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 15, 19, 25, 31, 39, 47, 59
Value range:
1
≤
Radius
≤
101
Minimum increment: 1
Recommended increment: 2
ModePercent (input_control) integer → (integer)
Filter Mode: 0 corresponds to a gray value opening , 50 corresponds to a median and 100 to a gray values closing.
Default: 10
Suggested values: 0, 2, 5, 10, 15, 20, 40, 50, 60, 80, 85, 90, 95, 98, 100
Value range:
0
≤
ModePercent
≤
100
Minimum increment: 1
Recommended increment: 2
Margin (input_control) string → (string / integer / real)
Border treatment.
Default: 'mirrored'
Suggested values: 'mirrored', 'cyclic', 'continued', 0, 30, 60, 90, 120, 150, 180, 210, 240, 255
Example (HDevelop)
read_image(Image,'fabrik') dual_rank(Image,ImageOpening,'circle',10,10,'mirrored') dev_display(ImageOpening)
Complexity
For each pixel: with F = area of the structuring element.
Result
If the parameter values are correct the operator
dual_rank returns the value 2 (
H_MSG_TRUE)
. The behavior in case
of empty input (no input images available) is set via the operator
set_system('no_object_result',<Result>).
If necessary an exception is raised.
Possible Predecessors
Possible Successors
threshold,
dyn_threshold,
sub_image,
regiongrowing
Alternatives
rank_image,
gray_closing,
gray_opening,
median_image
See also
gen_circle,
gen_rectangle1,
gray_erosion_rect,
gray_dilation_rect,
sigma_image
References
W. Eckstein, O. Munkelt “Extracting Objects from Digital Terrain Model” Remote Sensing and Reconstruction for Threedimensional Objects and Scenes, SPIE Symposium on Optical Science, Engeneering, and Instrumentation, July 1995, San Diego
Module
Foundation