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

import java.util.List;

import org.scijava.ops.image.imagemoments.AbstractImageMomentOp;
import net.imglib2.RandomAccessibleInterval;
import net.imglib2.loops.LoopBuilder;
import net.imglib2.type.numeric.RealType;
import net.imglib2.util.Intervals;

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

/**
 * Op to calculate the {@code imageMoments.centralMoment21}.
 *
 * @author Daniel Seebacher (University of Konstanz)
 * @author Christian Dietz (University of Konstanz)
 * @param <I> input type
 * @param <O> output type
 * @implNote op names='imageMoments.centralMoment21', label='Image Moment:
 *           CentralMoment21'
 */
public class DefaultCentralMoment21<I extends RealType<I>, O extends RealType<O>>
	implements AbstractImageMomentOp<I, O>
{

	@OpDependency(name = "imageMoments.moment00")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> moment00Func;

	@OpDependency(name = "imageMoments.moment01")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> moment01Func;

	@OpDependency(name = "imageMoments.moment10")
	private Computers.Arity1<RandomAccessibleInterval<I>, O> moment10Func;

	/**
	 * TODO
	 *
	 * @param input
	 * @param output
	 */
	@Override
	public void computeMoment(final RandomAccessibleInterval<I> input,
		final O output)
	{
		final var moment00 = output.createVariable();
		moment00Func.compute(input, moment00);
		final var moment01 = output.createVariable();
		moment01Func.compute(input, moment01);
		final var moment10 = output.createVariable();
		moment10Func.compute(input, moment10);

		final var centerX = moment10.copy();
		centerX.div(moment00);
		final var centerY = moment01.copy();
		centerY.div(moment00);

        var sums = LoopBuilder.setImages(input, Intervals.positions(input))
			.multiThreaded().forEachChunk(chunk -> {
                    var sum = output.createVariable();
				sum.setZero();
                    var x = output.createVariable();
                    var y = output.createVariable();
                    var temp = output.createVariable();
				chunk.forEachPixel((pixel, pos) -> {
					x.setReal(pos.getDoublePosition(0));
					x.sub(centerX);
					y.setReal(pos.getDoublePosition(1));
					y.sub(centerY);
					// temp = pixelVal * x * x * y
					temp.setReal(pixel.getRealDouble());
					temp.mul(x);
					temp.mul(x);
					temp.mul(y);
					sum.add(temp);
				});

				return sum;
			});

		output.setZero();
		for (var sum : sums)
			output.add(sum);
	}
}
