imgaborfilt

Apply Gabor filter or set of filters to 2-D image

Syntax

[mag,phase] = imgaborfilt(A,wavelength,orientation)

[mag,phase] = imgaborfilt(A,wavelength,orientation,Name,Value)

[mag,phase] = imgaborfilt(A,gaborbank)

Description

[mag,phase] = imgaborfilt(A,wavelength,orientation) computes the magnitude and phase response of a Gabor filter for the input grayscale image A. wavelength describes the wavelength in pixels/cycle of the sinusoidal carrier. orientation is the orientation of the filter in degrees. The output mag and phase are the magnitude and phase responses of the Gabor filter.

[mag,phase] = imgaborfilt(A,wavelength,orientation,Name,Value) applies a single Gabor filter using name-value pairs to control various aspects of filtering.

[mag,phase] = imgaborfilt(A,gaborbank) applies the array of Gabor filters, gaborbank, to the input image A. gaborbank is a 1-by-p array of Gabor objects, called a filter bank. mag and phase are image stacks where each plane in the stack corresponds to one of the outputs of the filter bank. For inputs of size A, the outputs mag and phase contain the magnitude and phase response for each filter in gaborbank and are of size m-by-n-by-p. Each plane in the magnitude and phase responses, mag(:,:,ind),phase(:,:,ind), is the result of applying the Gabor filter of the same index, gaborBank(ind).

Examples

Apply Single Gabor Filter to Input Image

Read image into the workspace.

I = imread('board.tif');

Convert image to grayscale.

I = rgb2gray(I);

Apply Gabor filter to image.

wavelength = 4;
orientation = 90;
[mag,phase] = imgaborfilt(I,wavelength,orientation);

Display original image with plots of the magnitude and phase calculated by the Gabor filter.

figure
subplot(1,3,1);
imshow(I);
title('Original Image');
subplot(1,3,2);
imshow(mag,[])
title('Gabor magnitude');
subplot(1,3,3);
imshow(phase,[]);
title('Gabor phase');

Apply Array of Gabor Filters to Input Image

Read image into the workspace.

I = imread('cameraman.tif');

Create array of Gabor filters, called a filter bank. This filter bank contains two orientations and two wavelengths.

gaborArray = gabor([4 8],[0 90]);

Apply filters to input image.

gaborMag = imgaborfilt(I,gaborArray);

Display results. The figure shows the magnitude response for each filter.

figure
subplot(2,2,1);
for p = 1:4
    subplot(2,2,p)
    imshow(gaborMag(:,:,p),[]);
    theta = gaborArray(p).Orientation;
    lambda = gaborArray(p).Wavelength;
    title(sprintf('Orientation=%d, Wavelength=%d',theta,lambda));
end

Input Arguments

A — 2-D grayscale image

numeric matrix

2-D grayscale image, specified as a numeric matrix.

If the image contains Infs or NaNs, the behavior of imgaborfilt is undefined because Gabor filtering is performed in the frequency domain.

For all input data types other than single, imgaborfilt performs the computation in double. Input images of type single are filtered in type single. Performance optimizations may result from casting the input image to single prior to calling imgaborfilt.

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

wavelength — Wavelength of sinusoidal carrier

number in the range [2,Inf)

Wavelength of the sinusoidal carrier, specified as a numeric scalar in the range [2,Inf), in pixels/cycle.

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

orientation — Orientation of filter

number in the range [0 360]

Orientation of filter in degrees, specified as a numeric scalar in the range [0 360], where the orientation is defined as the normal direction to the sinusoidal plane wave.

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

gaborbank — Array of Gabor filters

gabor object

Array of Gabor filters, specified as a gabor object. You must use the gabor function to create an array of Gabor filters.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: [mag,phase] = imgaborfilt(I,4,90,'SpatialFrequencyBandwidth',2);

'SpatialFrequencyBandwidth' — Spatial frequency bandwidth

1 (default) | numeric scalar

Spatial frequency bandwidth, specified as a numeric scalar in units of octaves. The spatial frequency bandwidth determines the cutoff of the filter response as frequency content in the input image varies from the preferred frequency, 1/lambda. Typical values for spatial-frequency bandwidth are in the range [0.5 2.5].

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

'SpatialAspectRatio' — Ratio of semi-major and semi-minor axes of Gaussian envelope

0.5 (default) | numeric scalar

Ratio of semi-major and semi-minor axes of Gaussian envelope (semi-minor/semi-major), specified as a numeric scalar. This parameter controls the ellipticity of the Gaussian envelope. Typical values for spatial aspect ratio are in the range [0.23 0.92].

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

Output Arguments

mag — Magnitude response for Gabor filter

numeric array

Magnitude response for the Gabor filter, returned as a numeric array.

Data Types: double

phase — Phase response for Gabor filter

numeric array of class double

Phase response for the Gabor filter, returned as a numeric array.

Data Types: double

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

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

• The wavelength, orientation, SpatialFrequencyBandwidth, and SpatialAspectRatio must be compile-time constants.

• The filter bank syntax is not supported.