imgaussfilt3

3-D Gaussian filtering of 3-D images

Syntax

B = imgaussfilt3(A)

B = imgaussfilt3(A,sigma)

B = imgaussfilt3(___,Name=Value)

Description

B = imgaussfilt3(A) filters 3-D image A with a 3-D Gaussian smoothing kernel with standard deviation of 0.5, and returns the filtered image in B.

B = imgaussfilt3(A,sigma) filters 3-D image A with a 3-D Gaussian smoothing kernel with standard deviation specified by sigma.

B = imgaussfilt3(___,Name=Value) uses name-value arguments to control aspects of the filtering.

Examples

Smooth MRI Volume with 3-D Gaussian Filter

Load MRI data and display it.

vol = load('mri');
figure
montage(vol.D)
title('Original image volume')

Smooth the image with a 3-D Gaussian filter.

siz = vol.siz;
vol = squeeze(vol.D);   
sigma = 2;
 
volSmooth = imgaussfilt3(vol, sigma);
  
figure
montage(reshape(volSmooth,siz(1),siz(2),1,siz(3)))
title('Gaussian filtered image volume')

Input Arguments

A — Image to be filtered

3-D numeric array

Image to be filtered, specified as a 3-D numeric array.

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

sigma — Standard deviation of the Gaussian distribution

0.5 (default) | positive number | 3-element vector of positive numbers

Standard deviation of the Gaussian distribution, specified as positive number or a 3-element vector of positive numbers. If sigma is a scalar, then imgaussfilt3 uses a cubic Gaussian kernel.

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

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: volSmooth = imgaussfilt3(vol,sigma,Padding="circular"); specifies circular padding.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: volSmooth = imgaussfilt3(vol,sigma,"Padding","circular");

FilterSize — Size of the Gaussian filter

positive, odd, integer | 3-element vector of positive, odd, integers

Size of the Gaussian filter, specified as a scalar or 3-element vector of positive, odd, integers. If you specify a scalar, then imgaussfilt3 uses a cubic filter. The default filter size is 2*ceil(2*sigma)+1.

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

Padding — Image padding

"replicate" (default) | "circular" | "symmetric" | numeric scalar

Image padding, specified as one of the values in the table.

Value	Description	Example
numeric scalar, X	Input array values outside the bounds of the array are assigned the value X.	$$\left[\begin{array}{ccc}3& 1& 4\\ 1& 5& 9\\ 2& 6& 5\end{array}\right]\to \left[\begin{array}{ccccccc}2& 2& 2& 2& 2& 2& 2\\ 2& 2& 2& 2& 2& 2& 2\\ 2& 2& 3& 1& 4& 2& 2\\ 2& 2& 1& 5& 9& 2& 2\\ 2& 2& 2& 6& 5& 2& 2\\ 2& 2& 2& 2& 2& 2& 2\\ 2& 2& 2& 2& 2& 2& 2\end{array}\right]$$ shows padding with the value 2.
"symmetric"	Input array values outside the bounds of the array are computed by mirror-reflecting the array across the array border.	$$\left[\begin{array}{ccc}3& 1& 4\\ 1& 5& 9\\ 2& 6& 5\end{array}\right]\to \left[\begin{array}{ccccccc}5& 1& 1& 5& 9& 9& 5\\ 1& 3& 3& 1& 4& 4& 1\\ 1& 3& 3& 1& 4& 4& 1\\ 5& 1& 1& 5& 9& 9& 5\\ 6& 2& 2& 6& 5& 5& 6\\ 6& 2& 2& 6& 5& 5& 6\\ 5& 1& 1& 5& 9& 9& 5\end{array}\right]$$
"replicate"	Input array values outside the bounds of the array are assumed to equal the nearest array border value.	$$\left[\begin{array}{ccc}3& 1& 4\\ 1& 5& 9\\ 2& 6& 5\end{array}\right]\to \left[\begin{array}{ccccccc}3& 3& 3& 1& 4& 4& 4\\ 3& 3& 3& 1& 4& 4& 4\\ 3& 3& 3& 1& 4& 4& 4\\ 1& 1& 1& 5& 9& 9& 9\\ 2& 2& 2& 6& 5& 5& 5\\ 2& 2& 2& 6& 5& 5& 5\\ 2& 2& 2& 6& 5& 5& 5\end{array}\right]$$
"circular"	Input array values outside the bounds of the array are computed by implicitly assuming the input array is periodic.	$$\left[\begin{array}{ccc}3& 1& 4\\ 1& 5& 9\\ 2& 6& 5\end{array}\right]\to \left[\begin{array}{ccccccc}5& 9& 1& 5& 9& 1& 5\\ 6& 5& 2& 6& 5& 2& 6\\ 1& 4& 3& 1& 4& 3& 1\\ 5& 9& 1& 5& 9& 1& 5\\ 6& 5& 2& 6& 5& 2& 6\\ 1& 4& 3& 1& 4& 3& 1\\ 5& 9& 1& 5& 9& 1& 5\end{array}\right]$$

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

FilterDomain — Domain in which to perform filtering

"auto" (default) | "frequency" | "spatial"

Domain in which to perform filtering, specified as one of the following values.

Filter Domain	Description
"auto"	Perform convolution in the spatial or frequency domain, based on internal heuristics.
"frequency"	Perform convolution in the frequency domain.
"spatial"	Perform convolution in the spatial domain.

Data Types: char | string

Output Arguments

B — Filtered image

numeric array

Filtered image, returned as a numeric array of the same data type and size as input image.

Tips

• If image A contains Infs or NaNs, then the behavior of imgaussfilt3 for frequency domain filtering is undefined. This can happen if you set the FilterDomain argument to "frequency" or if you set it to "auto" and imgaussfilt3 uses frequency domain filtering. To restrict the propagation of Infs and NaNs in the output in a manner similar to imfilter, consider setting the FilterDomain argument to "spatial".

• If you set the FilterDomain argument to "auto", then imgaussfilt3 uses an internal heuristic to determine whether spatial or frequency domain filtering is faster. This heuristic is machine-dependent and may vary for different configurations. For optimal performance, try both options, "spatial" and "frequency", to determine the best filtering domain for your image and kernel size.

• If you do not specify the Padding argument, then imgaussfilt3 uses "replicate" padding by default, which is different from the default used by imfilter.

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

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

This function fully supports GPU arrays. For more information, see Image Processing on a GPU.

Version History

Introduced in R2015a

R2022b: Support for thread-based environments

imgaussfilt3 now supports thread-based environments.