Index: trunk/pswarp/src/pswarpPixelFraction.c
===================================================================
--- trunk/pswarp/src/pswarpPixelFraction.c	(revision 15610)
+++ trunk/pswarp/src/pswarpPixelFraction.c	(revision 17780)
@@ -39,4 +39,7 @@
     long numPix = numCols * numRows;
 
+    // Range of valid pixels
+    int xMin = INT_MAX, xMax = -INT_MAX, yMin = INT_MAX, yMax = -INT_MAX;
+
     long numBad = 0;                     // Number of bad pixels
     for (int y = 0; y < numRows; y++) {
@@ -44,4 +47,17 @@
             if (mask->data.PS_TYPE_MASK_DATA[y][x] & maskVal) {
                 numBad++;
+            } else {
+                if (y > yMax) {
+                    yMax = y;
+                }
+                if (y < yMin) {
+                    yMin = y;
+                }
+                if (x > xMax) {
+                    xMax = x;
+                }
+                if (x < xMin) {
+                    xMin = x;
+                }
             }
         }
@@ -53,4 +69,9 @@
     if (stats) {
         psMetadataAddBool(stats, PS_LIST_HEAD, "ACCEPT", 0, "Accept this readout?", accept);
+
+        psMetadataAddS32(stats, PS_LIST_TAIL, "RANGE.XMIN", 0, "Minimum valid x value", xMin);
+        psMetadataAddS32(stats, PS_LIST_TAIL, "RANGE.XMAX", 0, "Maximum valid x value", xMax);
+        psMetadataAddS32(stats, PS_LIST_TAIL, "RANGE.YMIN", 0, "Minimum valid y value", yMin);
+        psMetadataAddS32(stats, PS_LIST_TAIL, "RANGE.YMAX", 0, "Maximum valid y value", yMax);
     }