Index: trunk/psModules/src/camera/pmFPAMaskWeight.c
===================================================================
--- trunk/psModules/src/camera/pmFPAMaskWeight.c	(revision 15307)
+++ trunk/psModules/src/camera/pmFPAMaskWeight.c	(revision 17249)
@@ -305,5 +305,5 @@
     for (int i = 0; i < readouts->n; i++) {
         pmReadout *readout = readouts->data[i]; // The readout
-        pmReadoutGenerateMaskWeight(readout, poisson, satMask, badMask);
+        success &= pmReadoutGenerateMaskWeight(readout, poisson, satMask, badMask);
     }
 
@@ -311,2 +311,66 @@
 }
 
+
+bool pmReadoutWeightRenorm(const pmReadout *readout, psMaskType maskVal, psStatsOptions meanStat,
+                           psStatsOptions stdevStat, int width, psRandom *rng)
+{
+    PM_ASSERT_READOUT_NON_NULL(readout, false);
+    PM_ASSERT_READOUT_IMAGE(readout, false);
+    PM_ASSERT_READOUT_WEIGHT(readout, false);
+    PS_ASSERT_INT_POSITIVE(width, false);
+
+    if (!psMemIncrRefCounter(rng)) {
+        rng = psRandomAlloc(PS_RANDOM_TAUS, 0);
+    }
+
+    psImage *image = readout->image, *mask = readout->mask, *weight = readout->weight; // Readout images
+    int numCols = image->numCols, numRows = image->numRows; // Size of images
+    int xNum = numCols / width + 1, yNum = numRows / width + 1; // Number of renormalisation regions
+    float xSize = numCols / (float)xNum, ySize = numRows / (float)yNum; // Size of renormalisation regions
+
+    psStats *meanStats = psStatsAlloc(meanStat), *stdevStats = psStatsAlloc(stdevStat); // Statistics
+    psVector *buffer = NULL;
+
+    for (int j = 0; j < yNum; j++) {
+        // Bounds in y
+        int yMin = j * ySize;
+        int yMax = (j + 1) * ySize;
+        for (int i = 0; i < xNum; i++) {
+            // Bounds in x
+            int xMin = i * xSize;
+            int xMax = (i + 1) * xSize;
+
+            psRegion region = psRegionSet(xMin, xMax, yMin, yMax); // Region of interest
+            psImage *subImage = psImageSubset(image, region); // Sub-image of the image pixels
+            psImage *subWeight = psImageSubset(weight, region); // Sub image of the weight pixels
+            psImage *subMask = mask ? psImageSubset(mask, region) : NULL; // Sub-image of the mask pixels
+
+            if (!psImageBackground(stdevStats, &buffer, subImage, subMask, maskVal, rng) ||
+                !psImageBackground(meanStats, &buffer, subWeight, subMask, maskVal, rng)) {
+                // Nothing we can do about it, but don't want to keel over and die, so do our best to flag it.
+                psString regionStr = psRegionToString(region); // String with region
+                psWarning("Unable to measure statistics over %s", regionStr);
+                psFree(regionStr);
+                psErrorClear();
+                psImageInit(subWeight, NAN);
+                if (subMask) {
+                    psImageInit(subMask, maskVal);
+                }
+            } else {
+                float meanVar = psStatsGetValue(meanStats, meanStat); // Mean of variance map
+                float stdev = psStatsGetValue(stdevStats, stdevStat); // Standard deviation of image
+                psBinaryOp(subWeight, subWeight, "*", psScalarAlloc(PS_SQR(stdev) / meanVar, PS_TYPE_F32));
+            }
+
+            psFree(subImage);
+            psFree(subWeight);
+            psFree(subMask);
+        }
+    }
+    psFree(meanStats);
+    psFree(stdevStats);
+    psFree(rng);
+    psFree(buffer);
+
+    return true;
+}