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 * Image processing operations for SciJava Ops.
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package org.scijava.ops.image.filter.hessian;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

import net.imglib2.RandomAccessibleInterval;
import net.imglib2.type.numeric.RealType;
import net.imglib2.view.Views;
import net.imglib2.view.composite.CompositeIntervalView;
import net.imglib2.view.composite.RealComposite;

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

/**
 * Hessian filter using the sobel filter with separated kernel.
 *
 * @author Eike Heinz, University of Konstanz
 * @param <T> type of input
 * @implNote op names='filter.hessian'
 */
public class HessianRAI<T extends RealType<T>> implements
	Function<RandomAccessibleInterval<T>, CompositeIntervalView<T, RealComposite<T>>>
{

	@OpDependency(name = "filter.partialDerivative")
	private Computers.Arity2<RandomAccessibleInterval<T>, Integer, RandomAccessibleInterval<T>> derivativeComputer;

	@OpDependency(name = "create.img")
	private Function<RandomAccessibleInterval<T>, RandomAccessibleInterval<T>> createRAI;

	/**
	 * TODO
	 *
	 * @param input
	 * @return the output
	 */
	@Override
	public CompositeIntervalView<T, RealComposite<T>> apply(
		RandomAccessibleInterval<T> input)
	{
		List<RandomAccessibleInterval<T>> derivatives = new ArrayList<>();
		for (var i = 0; i < input.numDimensions(); i++) {
            var derivative = createRAI.apply(input);
			derivativeComputer.compute(input, i, derivative);
			for (var j = 0; j < input.numDimensions(); j++) {
                var out = createRAI.apply(input);
				derivativeComputer.compute(derivative, j, out);
				derivatives.add(out);
			}
		}
        var stackedDerivatives = Views.stack(derivatives);
		return Views.collapseReal(stackedDerivatives);
	}

}
