stdfilt

Local standard deviation of image

Syntax

J = stdfilt(I)

J = stdfilt(I,nhood)

Description

J = stdfilt(I) performs standard deviation filtering of image I and returns the filtered image J. The value of each output pixel is the standard deviation of the 3-by-3 neighborhood around the corresponding input pixel. For pixels on the borders of I, stdfilt uses symmetric padding. In symmetric padding, the values of padding pixels are a mirror reflection of the border pixels in I.

J = stdfilt(I,nhood) specifies the neighborhood, nhood, used to compute the standard deviation.

Examples

Perform Standard Deviation Filtering

This example shows how to perform standard deviation filtering using stdfilt. Brighter pixels in the filtered image correspond to neighborhoods in the original image with larger standard deviations.

Read an image into the workspace.

I = imread('circuit.tif');

Perform standard deviation filtering using stdfilt.

J = stdfilt(I);

Show the original image and the processed image.

imshow(I)
title('Original Image')

figure
imshow(J,[])
title('Result of Standard Deviation Filtering')

Input Arguments

I — Image to be filtered

numeric array | logical array

Image to be filtered, specified as a numeric array or logical array of any dimension.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

nhood — Neighborhood

true(3) (default) | numeric array | logical array

Neighborhood, specified as a numeric or logical array containing 0s and 1s. The size of nhood must be odd in each dimension.

By default, stdfilt uses the neighborhood true(3). stdfilt determines the center element of the neighborhood by floor((size(nhood) + 1)/2).

To specify neighborhoods of various shapes, such as a disk, use the strel function to create a structuring element object of the desired shape. Then extract the neighborhood from the neighborhood property of the structuring element.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Output Arguments

J — Filtered image

numeric array

Filtered image, returned as a numeric array of the same size as the input image I. The data type of J is double.

Tips

• The double array J contains standard deviation values, which can exceed the range [0, 1]. Because some Image Processing Toolbox™ functions expect inputs of type double to be in the range [0, 1], to pass J as an input argument to these functions, use the rescale function to rescale the values of J to [0, 1].

• If the image contains Infs or NaNs, then the behavior of stdfilt is undefined. Propagation of Infs or NaNs might not be localized to the neighborhood around the Inf or NaN pixel.

Extended Capabilities

C/C++ Code Generation

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

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

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

• The filtering neighborhood must be two-dimensional.

For more information, see Image Processing on a GPU.

Version History

Introduced before R2006a

R2022a: Generate C code using MATLAB Coder

stdfilt now supports the generation of C code (requires MATLAB Coder).