Median Filter

Perform 2-D median filtering

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Library:
Computer Vision Toolbox / Analysis & Enhancement
Computer Vision Toolbox / Filtering

Description

TheMedian Filterblock applies a median filter to each pixel of an input image. For eachM-by-Nneighborhood, the filter replaces the central value with the median value of the neighborhood. If the neighborhood has a center element, the block replaces the center pixel with the median value, as shown in this figure.

If the neighborhood does not have an exact center, then the block has a bias toward the upper-left corner of the neighborhood. In this figure, the median value has been placed in the top-left pixel of the four pixels that meet at the center of the neighborhood.

The block pads the edges of the input image for filtering. This causes the pixels withinM/2pixels of the sides andN/2pixels of the top or bottom of the image to appear distorted.

The median value is less sensitive than the mean to extreme values. Thus,Median Filteris effective for removing salt-and-pepper noise from an image without significantly reducing the sharpness of the image.

Ports

Input

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`I`— Input image
matrix

Input image, specified as anM-by-Nmatrix.

`PVal`— Pad value
scalar

Pad value, specified as a scalar. The block uses this value for each element of the rows or columns added to the input image.

Dependencies

To enable this port:

Set theOutput sizeparameter toSame as input port I.
Set thePadding optionsparameter toConstant.
Set thePad value sourceparameter toInput port.

Output

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`Port_1`— Output image
matrix

Output image, returned as a matrix. The dimensions of the median-filtered output image are specified by theOutput sizeparameter.

Parameters

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`Neighborhood size`— Neighborhood window size
`[3 3]`(default) | positive integer | two-element vector of positive integers

Specify the window size of the neighborhood over which the block computes the median. If specified as a scalar, this value creates a square neighborhood with the specified number of rows and columns. If specified as a vector, the first element is the number of rows in the neighborhood, and the second element is the number of columns in the neighborhood.

`Output size`— Output sizing method
`Same as input port I`(default) |`Valid`

Specify the output sizing method as one of these options.

Same as input port I— The block computes the neighborhood median for the entire image, using padding to compute the boundary pixels. The output image has the same dimensions as the input image. Selecting this option enables thePadding optionsparameter.
Valid— The block computes the median where the neighborhood fits within the input image without padding. For an input image of sizeM-by-Nand neighborhood of sizeX-by-Y, the output image has the dimensions (M–X+1)-by-(N–Y+1).

`Padding options`— Padding method
`Symmetric`(default) |`Constant`|`Replicate`|`Circular`

Pad the image using one of these methods:

Constant— Pad image with a constant value. Selecting this option enables thePad value sourceparameter. For more information, seePad with Constant Value.
Replicate— Pad the image by repeating the border values of the input image. For more information, seePad by Repeating Border Values.
Symmetric— Pad the image using a mirror image of the input data. For more information, seePad with Mirror Image
Circular— Pad the image using a circular repetition of the elements in the input image. For more information, seePad Using Circular Repetition of Elements.

Dependencies

To enable this parameter, set theOutput sizeparameter toSame as input port I.

`Pad value source`— Source of constant padding value
`Specify via dialog`(default) |`Input port`

Specify the padding source asSpecify via dialogorInput port.

Specify via dialog— Specify a padding value using thePad valueparameter.
Input port— Specify a padding value using thePValinput port.

Dependencies

To enable this parameter, set theOutput sizeparameter toSame as input port I, and set thePadding optionsparameter toConstant.

`Pad value`— Pad value
`0`(default) | scalar

指定一个标量值来垫的形象.

Dependencies

To enable this port:

Set theOutput sizeparameter toSame as input port I.
Set thePadding optionsparameter toConstant.
Set thePad value sourceparameter toSpecify via dialog.

Model Examples

Remove Impulse Noise from Image

Remove impulse noise from an image by using a median filter.

Open Script

Block Characteristics

Data Types	`Boolean`\|`double`\|`fixed point`\|`integer`\|`single`
Multidimensional Signals	`no`
Variable-Size Signals	`yes`

References

[1] Gonzalez, Rafael C., and Richard E. Woods.Digital Image Processing. 2nd ed.Upper Saddle River, N.J: Prentice Hall, 2002.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

之前介绍过的R2006a

Median Filter

Description