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 * Image processing operations for SciJava Ops.
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package org.scijava.ops.image.imagemoments.hu;

import org.scijava.ops.image.imagemoments.AbstractImageMomentOp;
import net.imglib2.RandomAccessibleInterval;
import net.imglib2.type.numeric.RealType;

import org.scijava.function.Computers;
import org.scijava.ops.spi.Op;
import org.scijava.ops.spi.OpDependency;

/**
 * Op to calculate the {@code imageMoments.huMoment2}.
 *
 * @author Daniel Seebacher (University of Konstanz)
 * @author Christian Dietz (University of Konstanz)
 * @author Gabriel Selzer
 * @param <I> input type
 * @param <O> output type
 * @see <a href=
 *      "https://en.wikipedia.org/wiki/Image_moment#Rotation_invariants"> This
 *      page </a>
 * @implNote op names='imageMoments.huMoment2', label='Image Moment: HuMoment2'
 */
public class DefaultHuMoment2<I extends RealType<I>, O extends RealType<O>>
	implements AbstractImageMomentOp<I, O>
{

	@OpDependency(name = "imageMoments.normalizedCentralMoment20")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> normalizedCentralMoment20Func;

	@OpDependency(name = "imageMoments.normalizedCentralMoment02")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> normalizedCentralMoment02Func;

	@OpDependency(name = "imageMoments.normalizedCentralMoment11")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> normalizedCentralMoment11Func;

	/**
	 * TODO
	 *
	 * @param input
	 * @param output
	 */
	@Override
	public void computeMoment(final RandomAccessibleInterval<I> input,
		final O output)
	{

		final var n11 = output.createVariable();
		normalizedCentralMoment11Func.compute(input, n11);
		final var n20 = output.createVariable();
		normalizedCentralMoment20Func.compute(input, n20);
		final var n02 = output.createVariable();
		normalizedCentralMoment02Func.compute(input, n02);

		// n11Squared = 4 * n11 * n11
		final var n11Squared = n11.copy();
		n11Squared.mul(n11);
		output.setReal(4d);
		n11Squared.mul(output);

		// n2Squared = (n20 - n02)^2
		final var n2Squared = n20.copy();
		n2Squared.sub(n02);
		n2Squared.mul(n2Squared);

		// output = n2Squared + n11Squared
		output.set(n2Squared);
		output.add(n11Squared);
	}
}
