dn2radiance

Convert digital number to radiance

Since R2020b

Syntax

newhcube = dn2radiance(hcube)

newhcube = dn2radiance(hcube,'BlockSize',blocksize)

Description

newhcube = dn2radiance(hcube) converts the pixel values of the hyperspectral data cube from digital number to radiance values. The function returns a new hypercube object and the pixel values of the data cube are the top of atmosphere (TOA) radiances.

newhcube = dn2radiance(hcube,'BlockSize',blocksize) specifies the block size for block processing of the hyperspectral data cube by using the name-value pair argument 'BlockSize'.

The function divides the input image into distinct blocks, processes each block, and then concatenates the processed output of each block to form the output matrix. Hyperspectral images are multi-dimensional data sets that can be too large to fit in system memory in their entirety. This can cause the system to run out of memory while running the dn2radiance function. If you encounter such an issue, perform block processing by using this syntax.

For example, dn2radiance(hcube,'BlockSize',[50 50]) divides the input image into non-overlapping blocks of size 50-by-50 and then computes the radiance values for pixels in each block.

Note

To perform block processing by specifying the 'BlockSize' name-value pair argument, you must have MATLAB^® R2021a or a later release.

Note

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

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

Examples

Convert Digital Number to Radiance

Read hyperspectral data into the workspace.

hcube = hypercube('EO1H0440342002212110PY_cropped.hdr');

Determine the bad spectral band numbers using the BadBands parameter in the metadata.

bandNumber = find(~hcube.Metadata.BadBands);

Remove the bad spectral bands from the data cube.

hcube = removeBands(hcube,'BandNumber',bandNumber);

Compute the radiance values using the dn2radiance function.

newhcube = dn2radiance(hcube);

Read and display a spectral band image in the input and the output radiance data.

inputBand = hcube.DataCube;
radianceBand = newhcube.DataCube;
band = 80;
figure
subplot(1,2,1)
imagesc(inputBand(:,:,band))
title('Input Band')
axis off
subplot(1,2,2)
imagesc(radianceBand(:,:,band))
title('Radiance Band')
axis off
colormap gray   

Input Arguments

hcube — Input hyperspectral data

hypercube object

Input hyperspectral data, specified as a hypercube object. The DataCube property of the hypercube object stores the hyperspectral data cube. To convert the pixel values in digital numbers to radiance values, the Metadata property of the hypercube object must contain the Gain and Offset fields.

blocksize — Size of data blocks

2-element vector of positive integers

Size of the data blocks, specified as a 2-element vector of positive integers. The elements of the vector correspond to the number of rows and columns in each block, respectively. The size of the data blocks must be less than the size of the input image. Dividing the hyperspectral images into smaller blocks enables you process large data sets without running out of memory.

• If the blocksize value is too small, the memory usage of the function reduces at the cost of increased execution time.

• If the blocksize value is large or equal to the input image size, the execution time reduces at the cost of increased memory usage.

Example: 'BlockSize',[20 20] specifies the size of each data block as 20-by-20.

Output Arguments

newhcube — Output hyperspectral data

hypercube object

Output hyperspectral data, returned as a hypercube object. The pixels values of the output data cube are radiances specifying the amount of radiation from the surface being imaged. The radiance values are computed from digital numbers by using the equation:

$${\text{Radiance L}}_{\lambda }=\left(DN\times Gain\right)+Bias$$

Gain and Bias are the gain and offset values for each spectral bands respectively. The Metadata property of hypercube object contains the gain and the offset values.

Version History

Introduced in R2020b