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/* Copyright (c) 2008-2025 the MRtrix3 contributors.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Covered Software is provided under this License on an "as is"
* basis, without warranty of any kind, either expressed, implied, or
* statutory, including, without limitation, warranties that the
* Covered Software is free of defects, merchantable, fit for a
* particular purpose or non-infringing.
* See the Mozilla Public License v. 2.0 for more details.
*
* For more details, see http://www.mrtrix.org/.
*/
#include "command.h"
#include "image.h"
#include "math/SH.h"
#include "algo/threaded_loop.h"
using namespace MR;
using namespace App;
void usage ()
{
AUTHOR = "J-Donald Tournier (jdtournier@gmail.com)";
SYNOPSIS = "Compute the total power of a spherical harmonics image";
DESCRIPTION
+ "This command computes the sum of squared SH coefficients, "
"which equals the mean-squared amplitude "
"of the spherical function it represents."
+ Math::SH::encoding_description;
ARGUMENTS
+ Argument ("SH", "the input spherical harmonics coefficients image.").type_image_in ()
+ Argument ("power", "the output power image.").type_image_out ();
OPTIONS
+ Option ("spectrum", "output the power spectrum, i.e., the power contained within each harmonic degree (l=0, 2, 4, ...) as a 4-D image.");
}
void run () {
auto SH_data = Image<float>::open(argument[0]);
Math::SH::check (SH_data);
Header power_header (SH_data);
bool spectrum = get_options("spectrum").size();
int lmax = Math::SH::LforN (SH_data.size (3));
INFO ("calculating spherical harmonic power up to degree " + str (lmax));
if (spectrum)
power_header.size (3) = 1 + lmax/2;
else
power_header.ndim() = 3;
power_header.datatype() = DataType::Float32;
auto power_data = Image<float>::create(argument[1], power_header);
auto f1 = [&] (decltype(power_data)& P, decltype(SH_data)& SH) {
P.index(3) = 0;
for (int l = 0; l <= lmax; l+=2) {
float power = 0.0;
for (int m = -l; m <= l; ++m) {
SH.index(3) = Math::SH::index (l, m);
float val = SH.value();
power += Math::pow2 (val);
}
P.value() = power / (Math::pi * 4);
++P.index(3);
}
};
auto f2 = [&] (decltype(power_data)& P, decltype(SH_data)& SH) {
float power = 0.0;
for (int l = 0; l <= lmax; l+=2) {
for (int m = -l; m <= l; ++m) {
SH.index(3) = Math::SH::index (l, m);
float val = SH.value();
power += Math::pow2 (val);
}
}
P.value() = power / (Math::pi * 4);
};
auto loop = ThreadedLoop ("calculating SH power", SH_data, 0, 3);
if (spectrum)
loop.run(f1, power_data, SH_data);
else
loop.run(f2, power_data, SH_data);
}
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