diff --git a/public/java/src/org/broadinstitute/sting/gatk/walkers/qc/AssessReducedCoverage.java b/public/java/src/org/broadinstitute/sting/gatk/walkers/qc/AssessReducedCoverage.java
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@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2010 The Broad Institute
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
+ * THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package org.broadinstitute.sting.gatk.walkers.qc;
+
+import org.broadinstitute.sting.commandline.*;
+import org.broadinstitute.sting.gatk.CommandLineGATK;
+import org.broadinstitute.sting.gatk.contexts.AlignmentContext;
+import org.broadinstitute.sting.gatk.contexts.ReferenceContext;
+import org.broadinstitute.sting.gatk.filters.*;
+import org.broadinstitute.sting.gatk.refdata.RefMetaDataTracker;
+import org.broadinstitute.sting.gatk.walkers.*;
+import org.broadinstitute.sting.utils.GenomeLoc;
+import org.broadinstitute.sting.utils.help.DocumentedGATKFeature;
+import org.broadinstitute.sting.utils.pileup.PileupElement;
+import org.broadinstitute.sting.utils.pileup.ReadBackedPileup;
+
+import java.io.PrintStream;
+import java.util.*;
+
+/**
+ * Emits intervals present in either the original or reduced bam but not the other.
+ *
+ * <h2>Input</h2>
+ * <p>
+ * The original and reduced BAM files.
+ * </p>
+ *
+ * <h2>Output</h2>
+ * <p>
+ * A list of intervals present in one bam but not the other.
+ * </p>
+ *
+ * <h2>Examples</h2>
+ * <pre>
+ * java -Xmx2g -jar GenomeAnalysisTK.jar \
+ *   -I:original original.bam \
+ *   -I:reduced reduced.bam \
+ *   -R ref.fasta \
+ *   -T AssessReducedCoverage \
+ *   -o output.intervals
+ * </pre>
+ *
+ * @author ebanks
+ */
+@DocumentedGATKFeature( groupName = "Quality Control and Simple Analysis Tools", extraDocs = {CommandLineGATK.class} )
+@ReadFilters({UnmappedReadFilter.class, NotPrimaryAlignmentFilter.class, DuplicateReadFilter.class, FailsVendorQualityCheckFilter.class, BadCigarFilter.class})
+@Hidden
+public class AssessReducedCoverage extends LocusWalker<GenomeLoc, GenomeLoc> implements TreeReducible<GenomeLoc> {
+
+    private static final String original = "original";
+    private static final String reduced = "reduced";
+
+    @Output
+    protected PrintStream out;
+
+    @Override
+    public boolean includeReadsWithDeletionAtLoci() { return true; }
+
+    @Argument(fullName = "output_reduced_only_coverage", shortName = "output_reduced_only_coverage", doc = "Output an interval if the reduced bam has coverage where the original does not", required = false)
+    public boolean OUTPUT_REDUCED_ONLY_INTERVALS = false;
+
+    public void initialize() {}
+
+    public GenomeLoc map(RefMetaDataTracker tracker, ReferenceContext ref, AlignmentContext context) {
+
+        if ( tracker == null )
+            return null;
+
+        Set<String> tags = getAllTags(context.getBasePileup());
+        return (tags.contains(original) && !tags.contains(reduced)) ||
+                (OUTPUT_REDUCED_ONLY_INTERVALS && tags.contains(reduced) && !tags.contains(original)) ? ref.getLocus() : null;
+    }
+
+    private Set<String> getAllTags(final ReadBackedPileup pileup) {
+
+        final Set<String> tags = new HashSet<String>(10);
+
+        for ( final PileupElement p : pileup ) {
+            if ( (int)p.getQual() > 2 && p.getMappingQual() > 0 )
+                tags.addAll(getToolkit().getReaderIDForRead(p.getRead()).getTags().getPositionalTags());
+        }
+
+        return tags;
+    }
+
+    public void onTraversalDone(GenomeLoc sum) {
+        if ( sum != null )
+            out.println(sum);
+    }
+
+    public GenomeLoc reduceInit() {
+        return null;
+    }
+
+    public GenomeLoc treeReduce(GenomeLoc lhs, GenomeLoc rhs) {
+        if ( lhs == null )
+            return rhs;
+
+        if ( rhs == null )
+            return lhs;
+
+        // if contiguous, just merge them
+        if ( lhs.contiguousP(rhs) )
+            return getToolkit().getGenomeLocParser().createGenomeLoc(lhs.getContig(), lhs.getStart(), rhs.getStop());
+
+        // otherwise, print the lhs and start over with the rhs
+        out.println(lhs);
+        return rhs;
+    }
+
+    public GenomeLoc reduce(GenomeLoc value, GenomeLoc sum) {
+        if ( value == null )
+            return sum;
+
+        if ( sum == null )
+            return value;
+
+        // if contiguous, just merge them
+        if ( sum.contiguousP(value) )
+            return getToolkit().getGenomeLocParser().createGenomeLoc(sum.getContig(), sum.getStart(), value.getStop());
+
+        // otherwise, print the sum and start over with the value
+        out.println(sum);
+        return value;
+    }
+}
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