diff --git a/openbr/openbr_plugin.h b/openbr/openbr_plugin.h
index f6a2419..39dcd2e 100644
--- a/openbr/openbr_plugin.h
+++ b/openbr/openbr_plugin.h
@@ -906,8 +906,8 @@ public:
     bool selfSimilar; /*!< \brief \c true if the \em targetFiles == \em queryFiles, \c false otherwise. */
 
     virtual ~Output() {}
-    void setBlock(int rowBlock, int columnBlock); /*!< \brief Set the current block. */
-    void setRelative(float value, int i, int j); /*!< \brief Set a score relative to the current block. */
+    virtual void setBlock(int rowBlock, int columnBlock); /*!< \brief Set the current block. */
+    virtual void setRelative(float value, int i, int j); /*!< \brief Set a score relative to the current block. */
 
     static Output *make(const File &file, const FileList &targetFiles, const FileList &queryFiles); /*!< \brief Make an output from a file and gallery/probe file lists. */
     static void reformat(const FileList &targetFiles, const FileList &queryFiles, const File &simmat, const File &output); /*!< \brief Create an output from a similarity matrix and file lists. */
diff --git a/openbr/plugins/misc.cpp b/openbr/plugins/misc.cpp
index 765568d..35dd638 100644
--- a/openbr/plugins/misc.cpp
+++ b/openbr/plugins/misc.cpp
@@ -424,19 +424,21 @@ BR_REGISTER(Transform, SubjectTransform)
 
 /*!
  * \ingroup transforms
- * \brief Remove templates with the specified file extension.
+ * \brief Remove templates with the specified file extension or metadata value.
  * \author Josh Klontz \cite jklontz
  */
 class RemoveTemplatesTransform : public UntrainableMetaTransform
 {
     Q_OBJECT
     Q_PROPERTY(QString regexp READ get_regexp WRITE set_regexp RESET reset_regexp STORED false)
+    Q_PROPERTY(QString key READ get_key WRITE set_key RESET reset_key STORED false)
     BR_PROPERTY(QString, regexp, "")
+    BR_PROPERTY(QString, key, "")
 
     void project(const Template &src, Template &dst) const
     {
         const QRegularExpression re(regexp);
-        const QRegularExpressionMatch match = re.match(src.file.suffix());
+        const QRegularExpressionMatch match = re.match(key.isEmpty() ? src.file.suffix() : src.file.get<QString>(key));
         if (match.hasMatch()) dst = Template();
         else                  dst = src;
     }
diff --git a/openbr/plugins/output.cpp b/openbr/plugins/output.cpp
index d8692fb..7f873e3 100644
--- a/openbr/plugins/output.cpp
+++ b/openbr/plugins/output.cpp
@@ -138,17 +138,75 @@ BR_REGISTER(Output, meltOutput)
  * \brief \ref simmat output.
  * \author Josh Klontz \cite jklontz
  */
-class mtxOutput : public MatrixOutput
+class mtxOutput : public Output
 {
     Q_OBJECT
+    int headerSize, rowBlock, columnBlock;
+    cv::Mat blockScores;
 
     ~mtxOutput()
     {
-        if (file.isNull() || targetFiles.isEmpty() || queryFiles.isEmpty()) return;
-        BEE::writeSimmat(data,
-                         file.name,
-                         targetFiles.first().get<QString>("Gallery", "Unknown_Target"),
-                         queryFiles.first().get<QString>("Gallery", "Unknown_Query"));
+        writeBlock();
+    }
+
+    void setBlock(int rowBlock, int columnBlock)
+    {
+        if ((rowBlock == 0) && (columnBlock == 0)) {
+            // Initialize the file
+            QFile f(file);
+            QtUtils::touchDir(f);
+            if (!f.open(QFile::WriteOnly))
+                qFatal("Unable to open %s for writing.", qPrintable(file));
+            const int endian = 0x12345678;
+            QByteArray header;
+            header.append("S2\n");
+            header.append(qPrintable(targetFiles.first().get<QString>("Gallery", "Unknown_Target")));
+            header.append("\n");
+            header.append(qPrintable(queryFiles.first().get<QString>("Gallery", "Unknown_Query")));
+            header.append("\nMF ");
+            header.append(qPrintable(QString::number(queryFiles.size())));
+            header.append(" ");
+            header.append(qPrintable(QString::number(targetFiles.size())));
+            header.append(" ");
+            header.append(QByteArray((const char*)&endian, 4));
+            header.append("\n");
+            headerSize = f.write(header);
+            const float defaultValue = -std::numeric_limits<float>::max();
+            for (int i=0; i<targetFiles.size()*queryFiles.size(); i++)
+                f.write((const char*)&defaultValue, 4);
+            f.close();
+        } else {
+            writeBlock();
+        }
+
+        this->rowBlock = rowBlock;
+        this->columnBlock = columnBlock;
+        blockScores = cv::Mat(std::min(queryFiles.size()-rowBlock*Globals->blockSize, Globals->blockSize),
+                              std::min(targetFiles.size()-columnBlock*Globals->blockSize, Globals->blockSize),
+                              CV_32FC1);
+    }
+
+    void setRelative(float value, int i, int j)
+    {
+        blockScores.at<float>(i,j) = value;
+    }
+
+    void set(float value, int i, int j)
+    {
+        (void) value; (void) i; (void) j;
+        qFatal("Logic error.");
+    }
+
+    void writeBlock()
+    {
+        QFile f(file);
+        if (!f.open(QFile::ReadWrite))
+            qFatal("Unable to open %s for modifying.", qPrintable(file));
+        for (int i=0; i<blockScores.rows; i++) {
+            f.seek(headerSize + sizeof(float)*((rowBlock*Globals->blockSize+i)*targetFiles.size()+(columnBlock*Globals->blockSize)));
+            f.write((const char*)blockScores.row(i).data, sizeof(float)*blockScores.cols);
+        }
+        f.close();
     }
 };