Erosion (morphology)

This MedLibrary.org supplementary page on Erosion (morphology) is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:

Related Sponsors

BM Pharmacy Generic pharmaceuticals at unbeatable prices. Insomnia, men's health, hair health, pain control. bmpharmacy.com

Online Pharmacy Carisoprodol, tadalafil, sildenafil, vardenafil and more... xlpharmacy.com

MedBasket.com Discreet. Inexpensive. Fast shipping. Great selection. What more can we say? medbasket.com

Frugalmed 2000 reasons to shop with us first. frugalmed.com

Ads by Tiva

For use of "Erosion" in dermatopathology, see Erosion_(dermatopathology)

The erosion of the dark-blue square by a disk, resulting in the light-blue square.

Erosion is one of two fundamental operations (the other being dilation) in Morphological image processing from which all other morphological operations are based. It was originally defined for binary images, later being extended to grayscale images, and subsequently to complete lattices.

1 Binary erosion
- 1.1 Example
- 1.2 Properties
2 Grayscale erosion
3 Erosions on complete lattices
4 See also
5 References

Binary erosion

In binary morphology, an image is viewed as a subset of an Euclidean space $\mathbb{R}^d$ or the integer grid $\mathbb{Z}^d$ , for some dimension d.

The basic idea in binary morphology is to probe an image with a simple, pre-defined shape, drawing conclusions on how this shape fits or misses the shapes in the image. This simple "probe" is called structuring element, and is itself a binary image (i.e., a subset of the space or grid).

Let E be an Euclidean space or an integer grid, and A a binary image in E. The erosion of the binary image A by the structuring element B is defined by:

$A \ominus B = \{z\in E | B_{z} \subseteq A\}$ ,

where B_z is the translation of B by the vector z, i.e., $B_z = \{b+z|b\in B\}$ , $\forall z\in E$ .

When the structuring element B has a center (e.g., a disk or a square), and this center is located on the origin of E, then the erosion of A by B can be understood as the locus of points reached by the center of B when B moves inside A. For example, the erosion of a square of side 10, centered at the origin, by a disc of radius 2, also centered at the origin, is a square of side 6 centered at the origin.

The erosion of A by B is also given by the expression: $A \ominus B = \bigcap_{b\in B} A_{-b}$ .

Example

Suppose A is a 13 * 13 matrix and B is a 5 * 1 matrix:

    0 0 0 0 0 0 0 0 0 0 0 0 0  
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 1 1 1 1 1 1 1 0 0 0            1
    0 0 0 1 1 1 1 1 1 1 0 0 0            1
    0 0 0 1 1 1 1 1 1 1 0 0 0            1
    0 0 0 1 1 1 1 1 1 1 0 0 0            1
    0 0 0 1 1 1 1 1 1 1 0 0 0            1
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0

Assuming that the origin B is at its center, for each pixel in A superimpose the origin of B, if B is completely contained by A the pixel is retained, else deleted.

The Erosion of A by B is given by

    0 0 0 0 0 0 0 0 0 0 0 0 0  
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0            
    0 0 0 1 1 1 1 1 1 1 0 0 0            
    0 0 0 0 0 0 0 0 0 0 0 0 0            
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0 0 0 0

This means that only when B is completely contained inside A that the pixels values are retained, else it gets deleted or in other words it gets eroded.

Properties

The erosion is translation invariant.
It is increasing, that is, if $A\subseteq C$ , then $A\ominus B \subseteq C\ominus B$ .
If the origin of E belongs to the structuring element B, then the erosion is anti-extensive, i.e., $A\ominus B\subseteq A$ .
The erosion satisfies $(A\ominus B)\ominus C = A\ominus (B\oplus C)$ , where $\oplus$ denotes the morphological dilation.
The erosion is distributive over set intersection

Grayscale erosion

In grayscale morphology, images are functions mapping an Euclidean space or grid E into $\mathbb{R}\cup\{\infty,-\infty\}$ , where $\mathbb{R}$ is the set of reals, $\infty$ is an element larger than any real number, and $-\infty$ is an element smaller than any real number.

Denoting an image by f(x) and the grayscale structuring element by b(x), the grayscale erosion of f by b is given by

$(f\ominus b)(x)=\inf_{y\in E}[f(y)-b(y-x)]$ ,

where "inf" denotes the infimum.

Erosions on complete lattices

Complete lattices are partially ordered sets, where every subset has an infimum and a supremum. In particular, it contains a least element and a greatest element (also denoted "universe").

Let $(L,\leq)$ be a complete lattice, with infimum and minimum symbolized by $\wedge$ and $\vee$ , respectively. Its universe and least element are symbolized by U and $\emptyset$ , respectively. Moreover, let ${X i}$ be a collection of elements from L.

An erosion in $(L,\leq)$ is any operator $\varepsilon: L\rightarrow L$ that distributes over the infimum, and preserves the universe. I.e.:

$\bigwedge_{i}\varepsilon(X_i)=\varepsilon\left(\bigwedge_{i} X_i\right)$ ,
$\varepsilon(U)=U$ .

References

Image Analysis and Mathematical Morphology by Jean Serra, ISBN 0126372403 (1982)
Image Analysis and Mathematical Morphology, Volume 2: Theoretical Advances by Jean Serra, ISBN 0-12-637241-1 (1988)
An Introduction to Morphological Image Processing by Edward R. Dougherty, ISBN 0-8194-0845-X (1992)
Morphological Image Analysis; Principles and Applications by Pierre Soille, ISBN 3540-65671-5 (1999)
R. C. Gonzalez and R. E. Woods, Digital image processing, 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2002.

Wikipedia content modification information:

This page was last modified on 24 December 2008, at 07:01.

Wikipedia Authorship and Review

Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.

Wikipedia Usage Guidelines

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Erosion (morphology)".

The URL for this specific entry is:

http://medlibrary.org/medwiki/Erosion_(morphology)

All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.

Welcome to the MedLibrary.org Wikipedia Supplement on Erosion (morphology) -- Please Click to Return to Front Page