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2-D median filtering

`B = medfilt2(A)`

```
B = medfilt2(A, [m
n])
```

`B = medfilt2(___,padopt)`

`gpuarrayB = medfilt2(gpuarrayA,___)`

performs
median filtering of the matrix `B`

= medfilt2(`A`

)`A`

in two dimensions.
Each output pixel contains the median value in a 3-by-3 neighborhood
around the corresponding pixel in the input image. `medfilt2`

pads
the image with `0`

's on the edges, so the
median values for points within one-half the width of the neighborhood
(`[m n]/2`

) of the edges might appear distorted.

performs
the median filtering operation on a GPU. The input image and the output
image are gpuArrays. When working with gpuArrays, `gpuarrayB`

= medfilt2(`gpuarrayA`

,___)`medfilt2`

only
supports square neighborhoods with odd-length sides between 3 and
15. This syntax requires the Parallel Computing Toolbox™.

Median filtering is a nonlinear operation often used in image processing to reduce "salt and pepper" noise. A median filter is more effective than convolution when the goal is to simultaneously reduce noise and preserve edges. For information about performance considerations, see

`ordfilt2`

.If the input image

`A`

is of an integer class, all the output values are returned as integers. If the number of pixels in the neighborhood (i.e.,`m*n`

) is even, some of the median values might not be integers. In these cases, the fractional parts are discarded. Logical input is treated similarly. For example, the true median for the following 2-by-2 neighborhood in a`uint8`

array is 4.5, but`medfilt2`

discards the fractional part and returns 4.1 5 4 8

On the CPU, `medfilt2`

uses `ordfilt2`

to
perform the filtering.

[1] Lim, Jae S., *Two-Dimensional
Signal and Image Processing*, Englewood Cliffs, NJ, Prentice
Hall, 1990, pp. 469-476.

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