dual_rank — Opening, Median and Closing with circle or rectangle mask.
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 edges
are assumed to be constant (with the
indicated gray value).
'continued' Continuation of edge pixels.
'cyclic' Cyclic continuation of image edges.
'mirrored' Reflection of pixels at the image edges.
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.
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.
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 value: 'circle'
List of values: 'circle', 'square'
Radius (input_control) integer → (integer)
Radius of the filter mask.
Default value: 1
Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 15, 19, 25, 31, 39, 47, 59
Typical range of values: 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 value: 10
Suggested values: 0, 2, 5, 10, 15, 20, 40, 50, 60, 80, 85, 90, 95, 98, 100
Typical range of values: 0
≤
ModePercent
≤
100
Minimum increment: 1
Recommended increment: 2
Margin (input_control) string → (string / integer / real)
Border treatment.
Default value: 'mirrored'
Suggested values: 'mirrored', 'cyclic', 'continued', 0, 30, 60, 90, 120, 150, 180, 210, 240, 255
read_image(Image,'fabrik') dual_rank(Image,ImageOpening,'circle',10,10,'mirrored') dev_display(ImageOpening)
For each pixel: with F = area of the structuring element.
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.
threshold,
dyn_threshold,
sub_image,
regiongrowing
rank_image,
gray_closing,
gray_opening,
median_image
gen_circle,
gen_rectangle1,
gray_erosion_rect,
gray_dilation_rect,
sigma_image
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
Foundation