removeContinuum

Normalize spectral signature

Since R2024a

collapse all in page

    Syntax

    continuumRemovedRef = removeContinuum(reflectance)
    continuumRemovedRef = removeContinuum(reflectance,wavelength)
    continuumRemovedRef = removeContinuum(___,Method=method)

    Description

    Add-On Required: This feature requires the Hyperspectral Imaging Library for Image Processing Toolbox add-on.

    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.

    example

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

    example

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

    example

    Note

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

    Examples

    collapse all

    This example uses:

    Open Live Script

    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 = imhypercube("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
imshow(rgbImg)
title("RGB Image")

    Figure contains an axes object. The hidden axes object with title RGB Image contains an object of type image.

    figure
imagesc(scoreBeforeNormalization)
title("Spectral match before continuum removal")
axis image off
colormap(parula(5))
colorbar

    Figure contains an axes object. The hidden axes object with title Spectral match before continuum removal contains an object of type image.

    figure
imagesc(scoreAfterNormalization)
title("Spectral match after continuum removal")
axis image off
colormap(parula(5))
colorbar

    Figure contains an axes object. The hidden axes object with title Spectral match after continuum removal contains an object of type image.

    This example uses:

    Open Live Script

    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")

    Figure contains 2 axes objects. Axes object 1 with title Reflectance spectrum before continuum removal contains an object of type line. Axes object 2 with title Reflectance spectrum after continuum removal contains an object of type line.

    Input Arguments

    collapse all

    Reflectance spectrum from which to remove the continuum, specified as a structure, hypercube object, multicube 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.

    If reflectance is a multicube object, all its spectral bands must have the same data resolution. If all spectral bands of the multicube object do not have the same resolution, resample the bands using the resampleBands function, or select bands with uniform resolution using the selectBands function.

    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 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

    collapse all

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

    Version History

    Introduced in R2024a

    expand all

    See Also

    | | |

    Topics