offsetstrel

Morphological offset structuring element

Description

An offsetstrel object represents a nonflat morphological structuring element, which is an essential part of morphological dilation and erosion operations.

A nonflat structuring element is a matrix that identifies the pixel in the image being processed and defines the neighborhood used in the processing of that pixel. A nonflat structuring element contains finite values used as additive offsets in the morphological computation. The center pixel of the matrix, called the origin, identifies the pixel in the image that is being processed. Pixels in the neighborhood with the value -Inf are not used in the computation.

You can only use offsetstrel objects for morphological operations on grayscale images.

To create a flat structuring element, use strel.

Creation

Syntax

SE = offsetstrel(offset)

SE = offsetstrel('ball',r,h)

SE = offsetstrel('ball',r,h,n)

Description

SE = offsetstrel(offset) creates a nonflat structuring element with the additive offset specified in the matrix offset.

SE = offsetstrel('ball',r,h) creates a nonflat, ball-shaped structuring element whose radius in the x-y plane is r and whose maximum offset height is h. For improved performance, offsetstrel approximates this shape by a sequence of eight nonflat line-shaped structuring elements.

SE = offsetstrel('ball',r,h,n) creates a nonflat ball-shaped structuring element, where n specifies the number of nonflat, line-shaped structuring elements that offsetstrel uses to approximate the shape. Morphological operations using ball approximations run much faster when you specify a value for n greater than 0.

Input Arguments

offset — Values to be added to each pixel location in the neighborhood

numeric matrix

Values to be added to each pixel location in the neighborhood when performing the morphological operation, specified as a numeric matrix. Values that are -Inf are not considered in the computation.

Data Types: double

r — Radius of the ball-shaped structuring element

positive integer

Radius of the ball-shaped structuring element in the x-y plane, specified as a positive integer.

Data Types: double

h — Maximum offset height

real scalar

Maximum offset height, specified as a real scalar.

Data Types: double

n — Number of nonflat line-shaped structuring elements used to approximate the shape

8 (default) | positive even number

Number of nonflat line-shaped structuring elements used to approximate the shape, specified as a positive even number or 0.

Value of n	Behavior
n > 0	offsetstrel uses a sequence of n nonflat, line-shaped structuring elements to approximate the shape. n must be an even number.
n = 0	offsetstrel does not use any approximation. The structuring element members comprise all pixels whose centers are no greater than r away from the origin. The corresponding height values are determined from the formula of the ellipsoid specified by r and h.

Data Types: double

Properties

Offset — Structuring element neighborhood with offsets

numeric matrix

Structuring element neighborhood with offsets, specified as a numeric matrix.

Data Types: double

Dimensionality — Dimensions of structuring element

nonnegative scalar

Dimensions of structuring element, specified as a nonnegative scalar.

Data Types: double

Object Functions

imdilate	Dilate image
imerode	Erode image
imclose	Morphologically close image
imopen	Morphologically open image
imbothat	Bottom-hat filtering
imtophat	Top-hat filtering

decompose	Return sequence of decomposed structuring elements
reflect	Reflect structuring element
translate	Translate structuring element

Examples

Create Ball-shaped Structuring Element

Create a ball-shaped structuring element.

SE = offsetstrel('ball',5, 6)

SE = 
offsetstrel is a ball shaped offset structuring element with properties:

            Offset: [11x11 double]
    Dimensionality: 2

View the structuring element.

SE.Offset

ans = 11×11

      -Inf      -Inf         0    0.7498    1.4996    2.2494    1.4996    0.7498         0      -Inf      -Inf
      -Inf    0.7498    1.4996    2.2494    2.9992    2.9992    2.9992    2.2494    1.4996    0.7498      -Inf
         0    1.4996    2.2494    2.9992    3.7491    3.7491    3.7491    2.9992    2.2494    1.4996         0
    0.7498    2.2494    2.9992    3.7491    4.4989    4.4989    4.4989    3.7491    2.9992    2.2494    0.7498
    1.4996    2.9992    3.7491    4.4989    5.2487    5.2487    5.2487    4.4989    3.7491    2.9992    1.4996
    2.2494    2.9992    3.7491    4.4989    5.2487    5.9985    5.2487    4.4989    3.7491    2.9992    2.2494
    1.4996    2.9992    3.7491    4.4989    5.2487    5.2487    5.2487    4.4989    3.7491    2.9992    1.4996
    0.7498    2.2494    2.9992    3.7491    4.4989    4.4989    4.4989    3.7491    2.9992    2.2494    0.7498
         0    1.4996    2.2494    2.9992    3.7491    3.7491    3.7491    2.9992    2.2494    1.4996         0
      -Inf    0.7498    1.4996    2.2494    2.9992    2.9992    2.9992    2.2494    1.4996    0.7498      -Inf
      ⋮

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• offsetstrel supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• The 'ball' input argument must be compile-time constants.

• The methods associated with offsetstrel objects are not supported in code generation.

Version History

Introduced before R2006a