Index: trunk/psModules/src/imcombine/pmStack.c
===================================================================
--- trunk/psModules/src/imcombine/pmStack.c	(revision 42484)
+++ trunk/psModules/src/imcombine/pmStack.c	(revision 42555)
@@ -1548,4 +1548,5 @@
   } continue; }
 
+// combine pixels, averaging the inner XX percentile range, after rejecting 5-sigma outliers (robust 5 sigma)
 bool pmStackCombineByPercentile(
     pmReadout *combined,		// output stacked readout
@@ -1553,8 +1554,9 @@
     psArray *stackData,			// input exposures
     psF64 rejectFraction,               // outlier fraction of pixels to reject
+    int nminpix,			// minimum number of input values required to generate an output value
     psImageMaskType badMaskBits, 	// treat these bits as 'bad'
     psImageMaskType suspectMaskBits,	// treat these bits as 'suspect'
     psImageMaskType blankMaskBits       // use this mask value for pixels missing input data (distinguish between Ninput = 0 and Ngood = 0?)
-    ) {
+				) {
     int minInputCols, maxInputCols, minInputRows, maxInputRows; // Smallest and largest values to combine
     int xSize, ySize;                   // Size of the output image
@@ -1640,7 +1642,6 @@
 		nGood ++;
 	    }
-# define MIN_GOOD_PERCENTILE 3
-
-	    if (nGood < MIN_GOOD_PERCENTILE) ESCAPE;
+
+	    if (nGood < nminpix) ESCAPE;
 	    
 	    pixelData->n = nGood;
@@ -1677,5 +1678,5 @@
 	    int nGoodClip = Nhi - Nlo;
 
-	    int isTest = false;
+	    int isTest = true;
 	    isTest = isTest || ((x == 4743) && (y == 2903));
 	    isTest = isTest || ((x == 4953) && (y == 2919));
@@ -1702,6 +1703,6 @@
 	    // 'AT_LEAST' means we reject at least 'rejectFraction' of values, but it could
 	    // be a higher percentage for smaller numbers of inputs.
-# define AT_LEAST 1
-# define MIN_GOOD_PERCENTILE 3
+# define AT_LEAST 0
+
 # if (AT_LEAST)
 	    int Ns = MIN(MAX(1, 0.5*rejectFraction * nGoodClip), nGoodClip) + Nlo;
@@ -1713,5 +1714,5 @@
 	    int Npt = Ne - Ns;
 # endif
-	    if ((Npt < 1) || (nGood < MIN_GOOD_PERCENTILE)) ESCAPE;
+	    if ((Npt < 1) || (nGood < nminpix)) ESCAPE;
 
 	    // Set the given (suspect) mask bit if nGoodBits[i] > f*nGood in other words
Index: trunk/psModules/src/imcombine/pmStack.h
===================================================================
--- trunk/psModules/src/imcombine/pmStack.h	(revision 42484)
+++ trunk/psModules/src/imcombine/pmStack.h	(revision 42555)
@@ -52,4 +52,5 @@
     psArray *input,
     psF64 rejectFraction,
+    int nminpix,		     ///< Minimum number input per pixel to combine
     psImageMaskType badMaskBits, 	// treat these bits as 'bad'
     psImageMaskType suspectMaskBits,	// treat these bits as 'suspect'