removeContinuum

Normalize spectral signature

Since R2024a

Syntax

continuumRemovedRef = removeContinuum(reflectance)

continuumRemovedRef = removeContinuum(reflectance,wavelength)

continuumRemovedRef = removeContinuum(___,Method=method)

Description

The removeContinuum function normalizes the reflectance spectrum by removing the effect of the convex hull through division or subtraction. You can use continuum removal to reduce the influence of background spectra such as atmospheric effects and sensor artifacts, improving the accuracy of subsequent applications like spectral matching and target detection.

continuumRemovedRef = removeContinuum(reflectance) normalizes the reflectance spectrum reflectance by removing the convex hull using division.

continuumRemovedRef = removeContinuum(reflectance,wavelength) specifies the wavelengths wavelength within the reflectance spectrum.

continuumRemovedRef = removeContinuum(___,Method=method) specifies the method method for continuum removal.

Note

This function requires the Hyperspectral Imaging Library for Image Processing Toolbox™. You can install the Hyperspectral Imaging Library for Image Processing Toolbox from Add-On Explorer. For more information about installing add-ons, see Get and Manage Add-Ons.

The Hyperspectral Imaging Library for Image Processing Toolbox requires desktop MATLAB^®, as MATLAB Online™ or MATLAB Mobile™ do not support the library.

Examples

Improve Accuracy of Spectral Matching with Continuum Removal

Read the spectral signature of vegetation from the ECOSTRESS spectral library, to use as the reference spectrum.

lib = readEcostressSig("vegetation.tree.tsuga.canadensis.vswir.tsca-1-47.ucsb.asd.spectrum.txt");

Load a hyperspectral image into the workspace.

hcube = hypercube("paviaU.dat");

Colorize the hyperspectral image to get an RGB image.

rgbImg = colorize(hcube,Method="rgb",ContrastStretching=true);

Compute the distance scores of the spectrum of the hyperspectral image pixels with respect to the reference spectrum.

scoreBeforeNormalization = spectralMatch(lib,hcube);

Normalize the reference spectrum by removing its continuum.

continuumRemovedRef = removeContinuum(lib);

Normalize the hyperspectral image by removing its continuum.

continuumRemovedCube = removeContinuum(hcube);

Compute the distance scores of the normalized spectrum of the hyperspectral image pixels with respect to the normalized reference spectrum.

scoreAfterNormalization = spectralMatch(continuumRemovedRef,continuumRemovedCube);

Visualize the RGB image of the hyperspectral image, the distance score map before continuum removal, and the distance score map after continuum removal. The pixels with low distance scores are stronger matches to the reference spectrum, and are more likely to belong to the vegetation region. Observe that the distance scores after continuum removal are more accurate, as regions that do not have any vegetation cover have a significantly higher distance score after continuum removal.

figure
tiledlayout(3,1)
nexttile
imshow(rgbImg)
title("RGB Image")
nexttile
imagesc(scoreBeforeNormalization)
title("Spectral match before continuum removal")
axis image off
colormap(parula(5))
colorbar
nexttile
imagesc(scoreAfterNormalization)
title("Spectral match after continuum removal")
axis image off
colormap(parula(5))
colorbar

Remove Continuum of Reflectance Spectrum

Load a .mat file that contains the reflectance and the wavelength values of a spectrum into the workspace.

load spectralData.mat reflectance wavelength

Normalize the reflectance spectrum by removing its continuum. Remove the continuum by subtracting the convex hull from the reflectance spectrum.

continuumRemovedRef = removeContinuum(reflectance,wavelength,Method="subtraction");

Plot the reflectance spectrum before and after continuum removal as a function of the wavelengths.

tiledlayout(2,1)
nexttile
plot(wavelength,reflectance)
title("Reflectance spectrum before continuum removal")
nexttile
plot(wavelength,continuumRemovedRef)
title("Reflectance spectrum after continuum removal")

Input Arguments

reflectance — Reflectance spectrum from which to remove continuum

structure | hypercube object | numeric vector | 3-D numeric array

Reflectance spectrum from which to remove the continuum, specified as a structure, hypercube object, numeric vector, or 3-D numeric array.

If reflectance is a structure, it must contain Reflectance and Wavelength fields consisting of numeric vectors of equal length, such as a spectral signature read from the ECOSTRESS library using the readEcostressSig function.

If reflectance is a numeric vector or a 3-D numeric array, you must also specify the wavelength input argument.

wavelength — Wavelengths in reflectance spectrum

numeric vector

Wavelengths in the reflectance spectrum, specified as a numeric vector. If reflectance is a numeric vector of length C or a 3-D numeric array of size M-by-N-by-C, then you must specify wavelength as a vector of length C.

Data Types: single | double

method — Method for continuum removal

"division" (default) | "subtraction"

Method for continuum removal, specified as "division" or "subtraction". The method indicates whether the function removes the convex hull from the reflectance spectrum using division or subtraction.

Data Types: char | string

Output Arguments

continuumRemovedRef — Normalized spectrum

structure | hypercube object | numeric vector | 3-D numeric array

Normalized spectrum, returned as a structure, hypercube object, numeric vector, or 3-D numeric array of the same size and data type as reflectance.

Version History

Introduced in R2024a