Index: trunk/psModules/src/imcombine/pmStackReject.c
===================================================================
--- trunk/psModules/src/imcombine/pmStackReject.c	(revision 20561)
+++ trunk/psModules/src/imcombine/pmStackReject.c	(revision 20568)
@@ -126,5 +126,5 @@
 
 psPixels *pmStackReject(const psPixels *in, int numCols, int numRows, float threshold, float poorFrac,
-                        const psArray *subRegions, const psArray *subKernels)
+                        int stride, const psArray *subRegions, const psArray *subKernels)
 {
     PS_ASSERT_PIXELS_NON_NULL(in, NULL);
@@ -168,5 +168,5 @@
         psRegion *region = subRegions->data[i]; // Region of interest
         pmSubtractionKernels *kernels = subKernels->data[i]; // Kernel of interest
-        if (!pmSubtractionConvolve(convRO, NULL, inRO, NULL, NULL, 0, 0, 1.0, NAN,
+        if (!pmSubtractionConvolve(convRO, NULL, inRO, NULL, NULL, stride, 0, 0, 1.0, NAN,
                                    region, kernels, false, true)) {
             psError(PS_ERR_UNKNOWN, false, "Unable to convolve mask image in region %d.", i);
Index: trunk/psModules/src/imcombine/pmStackReject.h
===================================================================
--- trunk/psModules/src/imcombine/pmStackReject.h	(revision 20561)
+++ trunk/psModules/src/imcombine/pmStackReject.h	(revision 20568)
@@ -13,4 +13,5 @@
                         float threshold, ///< Threshold on convolved image, 0..1
                         float poorFrac, ///< Fraction for "poor"
+                        int stride,     ///< Size of convolution patches
                         const psArray *regions, ///< Array of image regions for image
                         const psArray *kernels ///< Array of kernel parameters for each region
Index: trunk/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.c	(revision 20561)
+++ trunk/psModules/src/imcombine/pmSubtraction.c	(revision 20568)
@@ -1088,7 +1088,7 @@
 
 bool pmSubtractionConvolve(pmReadout *out1, pmReadout *out2, const pmReadout *ro1, const pmReadout *ro2,
-                           psImage *subMask, psMaskType maskBad, psMaskType maskPoor, float poorFrac,
-                           float sysError, const psRegion *region, const pmSubtractionKernels *kernels,
-                           bool doBG, bool useFFT)
+                           psImage *subMask, int stride, psMaskType maskBad, psMaskType maskPoor,
+                           float poorFrac, float sysError, const psRegion *region,
+                           const pmSubtractionKernels *kernels, bool doBG, bool useFFT)
 {
     int numCols = 0, numRows = 0;       // Image dimensions
@@ -1124,4 +1124,9 @@
         PS_ASSERT_IMAGE_SIZE(subMask, numCols, numRows, false);
     }
+    PS_ASSERT_INT_NONNEGATIVE(stride, false);
+    PS_ASSERT_FLOAT_LARGER_THAN_OR_EQUAL(poorFrac, 0.0, false);
+    PS_ASSERT_FLOAT_LESS_THAN_OR_EQUAL(poorFrac, 1.0, false);
+    PS_ASSERT_FLOAT_LARGER_THAN_OR_EQUAL(sysError, 0.0, false);
+    PS_ASSERT_FLOAT_LESS_THAN_OR_EQUAL(sysError, 1.0, false);
     if (region && psRegionIsNaN(*region)) {
         psString string = psRegionToString(*region);
@@ -1212,5 +1217,4 @@
 
     int size = kernels->size;           // Half-size of kernel
-    int fullSize = 2 * size + 1;        // Full size of kernel
 
     // Get region for convolution: [xMin:xMax,yMin:yMax]
@@ -1236,8 +1240,13 @@
     psImageConvolveSetThreads(false);
 
-    for (int j = yMin; j < yMax; j += fullSize) {
-        int ySubMax = PS_MIN(j + fullSize, yMax); // Range for subregion of interest
-        for (int i = xMin; i < xMax; i += fullSize) {
-            int xSubMax = PS_MIN(i + fullSize, xMax); // Range for subregion of interest
+    if (stride == 0) {
+        // Use the full size of the kernel
+        stride = 2 * size + 1;
+    }
+
+    for (int j = yMin; j < yMax; j += stride) {
+        int ySubMax = PS_MIN(j + stride, yMax); // Range for subregion of interest
+        for (int i = xMin; i < xMax; i += stride) {
+            int xSubMax = PS_MIN(i + stride, xMax); // Range for subregion of interest
 
             psRegion *subRegion = psRegionAlloc(i, xSubMax, j, ySubMax); // Bounds of subtraction
Index: trunk/psModules/src/imcombine/pmSubtraction.h
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.h	(revision 20561)
+++ trunk/psModules/src/imcombine/pmSubtraction.h	(revision 20568)
@@ -6,6 +6,6 @@
  * @author GLG, MHPCC
  *
- * @version $Revision: 1.33 $ $Name: not supported by cvs2svn $
- * @date $Date: 2008-11-01 03:36:01 $
+ * @version $Revision: 1.34 $ $Name: not supported by cvs2svn $
+ * @date $Date: 2008-11-07 00:03:18 $
  * Copyright 2004-207 Institute for Astronomy, University of Hawaii
  */
@@ -103,4 +103,5 @@
                            const pmReadout *ro2, // Input image 2
                            psImage *subMask, ///< Subtraction mask (or NULL)
+                           int stride,  ///< Size of convolution patches
                            psMaskType maskBad, ///< Mask value to give bad pixels
                            psMaskType maskPoor, ///< Mask value to give poor pixels
Index: trunk/psModules/src/imcombine/pmSubtractionMatch.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 20561)
+++ trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 20568)
@@ -92,5 +92,5 @@
 
 bool pmSubtractionMatch(pmReadout *conv1, pmReadout *conv2, const pmReadout *ro1, const pmReadout *ro2,
-                        int footprint, float regionSize, float stampSpacing, float threshold,
+                        int footprint, int stride, float regionSize, float stampSpacing, float threshold,
                         const psArray *sources, const char *stampsName,
                         pmSubtractionKernelsType type, int size, int spatialOrder,
@@ -139,4 +139,5 @@
 
     PS_ASSERT_INT_NONNEGATIVE(footprint, false);
+    PS_ASSERT_INT_NONNEGATIVE(stride, false);
     // regionSize can be just about anything (except maybe negative, but it can be NAN)
     PS_ASSERT_FLOAT_LARGER_THAN(stampSpacing, 0.0, false);
@@ -396,5 +397,5 @@
 
             psTrace("psModules.imcombine", 2, "Convolving...\n");
-            if (!pmSubtractionConvolve(conv1, conv2, ro1, ro2, subMask, maskBad, maskPoor, poorFrac,
+            if (!pmSubtractionConvolve(conv1, conv2, ro1, ro2, subMask, stride, maskBad, maskPoor, poorFrac,
                                        sysError, region, kernels, true, useFFT)) {
                 psError(PS_ERR_UNKNOWN, false, "Unable to convolve image.");
Index: trunk/psModules/src/imcombine/pmSubtractionMatch.h
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionMatch.h	(revision 20561)
+++ trunk/psModules/src/imcombine/pmSubtractionMatch.h	(revision 20568)
@@ -16,4 +16,5 @@
                         // Stamp parameters
                         int footprint,  ///< Stamp half-size
+                        int stride,     ///< Size for convolution patches
                         float regionSize, ///< Typical size of iso-kernel regions
                         float stampSpacing, ///< Typical spacing between stamps