median ( Image : ImageMedian : MaskType, Radius, Margin : )

Median filtering with different rank masks.

The operator rank__ carries out a non-linear smoothing of the gray values of all input images (Image). The shift mask (MaskType) is transmitted in the form of an object (more precisely: its region). Several margin controls can be chosen for filtering (Margin):

    0...255   pixels outside of the image edges
              are assumed constant (with the indicated
              gray value).
    -1        Continuation of edge pixels.
    -2        Cyclic continuation of image edges.
    -3        Reflection of pixels at the image edges.
The indicated mask (= region of the mask image) is put over the image to be filtered in such a way that the center of the mask touches all pixels of the objects once. For each of these pixels all neighboring pixels covered by the mask are sorted in an ascending sequence according to their gray values. Thus, each of these sorted gray value sequences contains exactly as many gray values as the mask has pixels. From these sequences the median is selected and entered as resulting gray value at the corresponding output image.


Parameters

Image (input_object)
image(-array) -> object : byte
Image to be filtered.

ImageMedian (output_object)
image(-array) -> object : byte
Median filtered image.

MaskType (input_control)
string -> string
Type of median mask.
Default value: 'circle'
List of values: 'circle', 'rectangle'

Radius (input_control)
integer -> integer
Radius of median mask.
Default value: 1
Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 15, 19, 25, 31, 39, 47, 59
Range of values: 1 <= Radius <= 101
Minimum increment: 1
Recommended increment: 2

Margin (input_control)
integer -> integer
Margin control: 0...255 (constant), -1 (edge pixels continued), -2 (cyclic continuation), -3 (reflection).
Default value: -3
Range of values: -3 <= Margin <= 255


Example
read_image(:Image:'fabrik':) >
median(Image:Median:'circle',3,-1:) > 
disp_image(MedianWeighted:::).

Complexity

For each pixel: O(sqrt(F) * 5) with F = area of MaskType.


Result

If the parameter values are correct the operator median returns the value TRUE. The behavior in case of empty input (no input images available) is set via the operator set_system(::'no_object_result',<Resultat>:). If necessary an exception is raised.


Possible Predecessors

read_image


Possible Successors

threshold__, dyn_threshold__, regiongrowing__


Alternatives

rank__


See also

circle, rectangle1, min1__, max1__


References

R. Haralick, L. Shapiro; "Computer and Robot Vision"; Addison-Wesley, 1992, Seite 318-319



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