diff --git a/openbr/plugins/output/knn.cpp b/openbr/plugins/output/knn.cpp
index 0160ecb..bedd989 100644
--- a/openbr/plugins/output/knn.cpp
+++ b/openbr/plugins/output/knn.cpp
@@ -6,44 +6,80 @@
 namespace br
 {
 
+typedef QPair<float,int> Pair;
+
 /*!
  * \ingroup outputs
  * \brief Outputs the k-Nearest Neighbors from the gallery for each probe.
  * \author Ben Klein \cite bhklein
  */
-class knnOutput : public MatrixOutput
+class knnOutput : public Output
 {
     Q_OBJECT
 
+    int rowBlock, columnBlock;
+    size_t headerSize, k;
+    cv::Mat blockScores;
+
     ~knnOutput()
     {
-        size_t num_probes = (size_t)queryFiles.size();
-        if (targetFiles.isEmpty() || queryFiles.isEmpty()) return;
-        size_t k = file.get<size_t>("k", 20);
+        writeBlock();
+    }
 
-        if ((size_t)targetFiles.size() < k)
-            qFatal("Gallery size %s is smaller than k = %s.", qPrintable(QString::number(targetFiles.size())), qPrintable(QString::number(k)));
+    void setBlock(int rowBlock, int columnBlock)
+    {
+        if ((rowBlock == 0) && (columnBlock == 0)) {
+            k = file.get<size_t>("k", 20);
+            QFile f(file);
+            if (!f.open(QFile::WriteOnly))
+                qFatal("Unable to open %s for writing.", qPrintable(file));
+            size_t querySize = (size_t)queryFiles.size();
+            f.write((const char*) &querySize, sizeof(size_t));
+            f.write((const char*) &k, sizeof(size_t));
+            headerSize = 2 * sizeof(size_t);
+        } else {
+            writeBlock();
+        }
 
-        QFile f(file);
-        if (!f.open(QFile::WriteOnly))
-            qFatal("Unable to open %s for writing.", qPrintable(file));
-        f.write((const char*) &num_probes, sizeof(size_t));
-        f.write((const char*) &k, sizeof(size_t));
+        this->rowBlock = rowBlock;
+        this->columnBlock = columnBlock;
+
+        int matrixRows  = std::min(queryFiles.size()-rowBlock*this->blockRows, blockRows);
+        int matrixCols  = std::min(targetFiles.size()-columnBlock*this->blockCols, blockCols);
+
+        blockScores = cv::Mat(matrixRows, matrixCols, CV_32FC1);
+    }
 
-        QVector<Candidate> neighbors; neighbors.reserve(num_probes*k);
+    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));
+        QVector<Candidate> neighbors; neighbors.reserve(k * blockScores.rows);
 
-        for (size_t i=0; i<num_probes; i++) {
-            typedef QPair<float,int> Pair;
+        for (int i=0; i<blockScores.rows; i++) {
             size_t rank = 0;
-            foreach (const Pair &pair, Common::Sort(OpenCVUtils::matrixToVector<float>(data.row(i)), true)) {
-                if (QString(targetFiles[pair.second]) != QString(queryFiles[i])) {
+            foreach (const Pair &pair, Common::Sort(OpenCVUtils::matrixToVector<float>(blockScores.row(i)), true)) {
+                if (QString(targetFiles[pair.second]) != QString(queryFiles[rowBlock*this->blockRows+i])) {
                     Candidate candidate((size_t)pair.second, pair.first);
                     neighbors.push_back(candidate);
                     if (++rank >= k) break;
                 }
             }
         }
-        f.write((const char*) neighbors.data(), num_probes * k * sizeof(Candidate));
+        f.seek(headerSize + sizeof(Candidate)*quint64(rowBlock*this->blockRows)*k);
+        f.write((const char*) neighbors.data(), blockScores.rows * k * sizeof(Candidate));
         f.close();
     }
 };