Index: branches/eam_branches/20091201/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- branches/eam_branches/20091201/psModules/src/imcombine/pmSubtraction.c	(revision 26787)
+++ branches/eam_branches/20091201/psModules/src/imcombine/pmSubtraction.c	(revision 26794)
@@ -1325,6 +1325,7 @@
 
     // Calculate covariances
-    // This can take a while, so we only do it for a single instance
-    // XXX psImageCovarianceCalculate could be multithreaded
+    // This can be fairly involved, so we only do it for a single instance
+    // Enable threads for covariance calculation, since we're not threading on top of it.
+    oldThreads = psImageCovarianceSetThreads(true);
     if (kernels->mode == PM_SUBTRACTION_MODE_1 || kernels->mode == PM_SUBTRACTION_MODE_DUAL) {
         psKernel *kernel = pmSubtractionKernel(kernels, 0.0, 0.0, false); // Convolution kernel
@@ -1340,4 +1341,5 @@
         psFree(kernel);
     }
+    psImageCovarianceSetThreads(oldThreads);
 
     // Copy anything that wasn't convolved