imgaussfilt

2-D Gaussian filtering of images

Syntax

B = imgaussfilt(A)

B = imgaussfilt(A,sigma)

B = imgaussfilt(___,Name=Value)

Description

B = imgaussfilt(A) filters image A with a 2-D Gaussian smoothing kernel with standard deviation of 0.5, and returns the filtered image in B.

B = imgaussfilt(A,sigma) filters image A with a 2-D Gaussian smoothing kernel with standard deviation specified by sigma.

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

Examples

Smooth Image with Gaussian Filter

Read image to be filtered.

I = imread("cameraman.tif");

Filter the image with a Gaussian filter with standard deviation of 2.

Iblur = imgaussfilt(I,2);

Display the original and filtered image in a montage.

montage({I,Iblur})
title("Original Image (Left) Vs. Gaussian Filtered Image (Right)")

Input Arguments

A — Image to be filtered

numeric array

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

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

sigma — Standard deviation of Gaussian distribution

0.5 (default) | positive number | 2-element vector of positive numbers

Standard deviation of the Gaussian distribution, specified as a positive number or a 2-element vector of positive numbers. If you specify a scalar, then imgaussfilt uses a square 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: B = imgaussfilt(A,FilterSize=3); specifies a filter of size 3.

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

Example: B = imgaussfilt(A,"FilterSize",3);

FilterSize — Size of Gaussian filter

positive, odd integer | 2-element vector of positive, odd integers

Size of the Gaussian filter, specified as a positive, odd integer or 2-element vector of positive, odd integers. If you specify a scalar, then imgaussfilt uses a square 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) | numeric scalar | "circular" | "symmetric"

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) | "spatial" | "frequency"

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

Value	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 class and size as the input image, A.

Tips

• If image A contains elements with values Inf or NaN, then the behavior of imgaussfilt for frequency domain filtering is undefined. This can happen if you set the FilterDomain name-value argument to "frequency" or if you set it to "auto" and imgaussfilt 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 name-value argument to "spatial".

• If you set the FilterDomain name-value argument to "auto", then imgaussfilt 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 name-value argument, then imgaussfilt uses "replicate" padding by default, which is different from the default used by imfilter.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

• imgaussfilt supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imgaussfilt generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Types of Code Generation Support in Image Processing Toolbox.

• imgaussfilt does not support the FilterDomain name-value argument specified as "frequency". Filtering is always done in the spatial domain in generated code.

• When generating code, all string and character vector input arguments must be compile-time constants.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Usage notes and limitations:

• imgaussfilt does not support the FilterDomain name-value argument specified as "frequency". Filtering is always done in the spatial domain in generated code.

• When generating code, all string and character vector input arguments must be compile-time constants.

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

imgaussfilt now supports thread-based environments.