/*
 * #%L
 * ImageJ software for multidimensional image processing and analysis.
 * %%
 * Copyright (C) 2014 - 2015 Board of Regents of the University of
 * Wisconsin-Madison, University of Konstanz and Brian Northan.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * #L%
 */

package net.imagej.ops.stats.variance;

import java.util.Iterator;

import net.imagej.ops.AbstractComputerOp;
import net.imagej.ops.Ops;
import net.imglib2.type.numeric.RealType;
import net.imglib2.type.numeric.real.DoubleType;

import org.scijava.Priority;
import org.scijava.plugin.Plugin;

@Plugin(type = Ops.Stats.Variance.class, name = Ops.Stats.Variance.NAME,
	priority = Priority.LOW_PRIORITY + 1)
public class VarianceRealTypeDirect<T extends RealType<T>> extends
	AbstractComputerOp<Iterable<T>, DoubleType> implements
	VarianceOp<T, DoubleType>
{

	@Override
	public void compute(final Iterable<T> input, final DoubleType output) {
		double sum = 0;
		double sumSqr = 0;
		int n = 0;

		final Iterator<T> it = input.iterator();
		while (it.hasNext()) {
			final double px = it.next().getRealDouble();
			++n;
			sum += px;
			sumSqr += px * px;
		}

		output.setReal((sumSqr - (sum * sum / n)) / (n - 1));
	}

}

/*
 * #%L
 * ImageJ software for multidimensional image processing and analysis.
 * %%
 * Copyright (C) 2014 - 2015 Board of Regents of the University of
 * Wisconsin-Madison, University of Konstanz and Brian Northan.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * #L%
 */

package net.imagej.ops.stats.variance;

import java.util.Iterator;

import net.imagej.ops.AbstractComputerOp;
import net.imagej.ops.Ops;
import net.imglib2.type.numeric.RealType;

import org.scijava.Priority;
import org.scijava.plugin.Plugin;

@Plugin(type = Ops.Stats.Variance.class, name = Ops.Stats.Variance.NAME,
	priority = Priority.LOW_PRIORITY + 1)
public class VarianceRealTypeDirect<T extends RealType<T>, O extends RealType<O>> extends
	AbstractComputerOp<Iterable<T>, O> implements
	VarianceOp<T, O>
{

	@Override
	public void compute(final Iterable<T> input, final O output) {
		double sum = 0;
		double sumSqr = 0;
		int n = 0;

		final Iterator<T> it = input.iterator();
		while (it.hasNext()) {
			final double px = it.next().getRealDouble();
			++n;
			sum += px;
			sumSqr += px * px;
		}

		output.setReal((sumSqr - (sum * sum / n)) / (n - 1));
	}

}

Use generics for VarianceRealTypeDirect output