sigma_image
— Non-linear smoothing with the sigma filter.
sigma_image(Image : ImageSigma : MaskHeight, MaskWidth, Sigma : )
The operator sigma_image
carries out a non-linear smoothing
of the gray values of all input images (Image
). All
pixels in a rectangular window (MaskHeight x
MaskWidth) are used to determine
the new gray value of the central pixel of this window.
First, the gray value standard deviation
of all pixels in the window is calculated. Then, all pixels of the
window with a gray value that differs from the gray value of the
central pixel by less than Sigma
times this standard
deviation are used to calculate the new gray value of the central
pixel. The gray value of the central pixel is the average of the
gray values of the selected pixels. If no pixel could be selected
for the averaging of the gray values, the gray value of the central
pixel remains unchanged.
For an explanation of the concept of smoothing filters see the introduction of chapter Filters / Smoothing.
If even values instead of odd values are given for
MaskHeight
or MaskWidth
, the routine uses the next
larger odd values instead (this way the center of the filter mask is
always explicitly determined).
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 / cyclic / int1 / int2 / uint2 / int4 / real)
Image to be smoothed.
ImageSigma
(output_object) (multichannel-)image(-array) →
object (byte / cyclic / int1 / int2 / uint2 / int4 / real)
Smoothed image.
MaskHeight
(input_control) extent.y →
(integer)
Height of the mask (number of lines).
Default value: 5
Suggested values: 3, 5, 7, 9, 11, 13, 15
Typical range of values: 3
≤
MaskHeight
Minimum increment: 2
Recommended increment: 2
Restriction: odd(MaskHeight)
MaskWidth
(input_control) extent.x →
(integer)
Width of the mask (number of columns).
Default value: 5
Suggested values: 3, 5, 7, 9, 11, 13, 15
Typical range of values: 3
≤
MaskWidth
Minimum increment: 2
Recommended increment: 2
Restriction: odd(MaskWidth)
Sigma
(input_control) integer →
(integer)
Max. deviation to the average.
Default value: 3
Suggested values: 3, 5, 7, 9, 11, 20, 30, 50
Typical range of values: 0
≤
Sigma
Minimum increment: 1
Recommended increment: 2
read_image(Image,'fabrik') sigma_image(Image,ImageSigma,5,5,3) dev_display(ImageSigma)
For each pixel: O(MaskHeight*MaskWidth).
If the parameter values are correct the operator sigma_image
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
,
regiongrowing
anisotropic_diffusion
,
rank_image
smooth_image
,
binomial_filter
,
gauss_filter
,
mean_image
R. Haralick, L. Shapiro; “Computer and Robot Vision”; Addison-Wesley, 1992, Seite 325
Foundation