Index: /branches/eam_branches/20091201/psModules/src/imcombine/pmSubtractionMatch.c
===================================================================
--- /branches/eam_branches/20091201/psModules/src/imcombine/pmSubtractionMatch.c	(revision 26732)
+++ /branches/eam_branches/20091201/psModules/src/imcombine/pmSubtractionMatch.c	(revision 26733)
@@ -215,4 +215,26 @@
 }
 
+bool pmSubtractionMaskInvalid (const pmReadout *readout, psImageMaskType maskVal) {
+
+    if (!readout) return true;
+
+    psImage *image = readout->image;
+    psImage *mask  = readout->mask;
+    psImage *variance = readout->variance;
+    for (int y = 0; y < image->numRows; y++) {
+        for (int x = 0; x < image->numCols; x++) {
+            if (mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskVal) continue;
+            bool valid = false;
+            valid = isfinite(image->data.F32[y][x]);
+            if (variance) {
+                valid &= isfinite(variance->data.F32[y][x]);
+            }
+            if (valid) continue;
+            mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] = maskVal;
+        }
+    }
+
+    return true;
+}
 
 bool pmSubtractionMatchPrecalc(pmReadout *conv1, pmReadout *conv2, const pmReadout *ro1, const pmReadout *ro2,
@@ -294,4 +316,7 @@
     }
 
+    pmSubtractionMaskInvalid(ro1, maskVal);
+    pmSubtractionMaskInvalid(ro2, maskVal);
+
     psImage *subMask = pmSubtractionMask(ro1->mask, ro2 ? ro2->mask : NULL, maskVal, size, 0,
                                          badFrac, mode); // Subtraction mask
@@ -428,4 +453,7 @@
 
     memCheck("start");
+
+    pmSubtractionMaskInvalid(ro1, maskVal);
+    pmSubtractionMaskInvalid(ro2, maskVal);
 
     subMask = pmSubtractionMask(ro1->mask, ro2 ? ro2->mask : NULL, maskVal, size, footprint,