Index: branches/eam_branches/20091201/ppStack/src/ppStackPrepare.c
===================================================================
--- branches/eam_branches/20091201/ppStack/src/ppStackPrepare.c	(revision 26832)
+++ branches/eam_branches/20091201/ppStack/src/ppStackPrepare.c	(revision 26833)
@@ -239,24 +239,29 @@
         havePSFs = true;
 
-        double sumFWHM = 0.0;           // FWHM for image
-        int numFWHM = 0;                // Number of FWHM measurements
-        for (int y = 0; y < psf->trendNy; y++) {
-            float yPos = ((float)y + 0.5) / (float)psf->trendNy * numRows;
-            for (int x = 0; x < psf->trendNx; x++) {
-                float xPos = ((float)x + 0.5) / (float)psf->trendNx * numCols;
-                float fwhm = pmPSFtoFWHM(psf, xPos, yPos); // FWHM for image
-                if (isfinite(fwhm)) {
-                    sumFWHM += fwhm;
-                    numFWHM++;
+        if (psf->trendNx > 0 && psf->trendNy > 0) {
+            double sumFWHM = 0.0;           // FWHM for image
+            int numFWHM = 0;                // Number of FWHM measurements
+            for (int y = 0; y < psf->trendNy; y++) {
+                float yPos = ((float)y + 0.5) / (float)psf->trendNy * numRows;
+                for (int x = 0; x < psf->trendNx; x++) {
+                    float xPos = ((float)x + 0.5) / (float)psf->trendNx * numCols;
+                    float fwhm = pmPSFtoFWHM(psf, xPos, yPos); // FWHM for image
+                    if (isfinite(fwhm)) {
+                        sumFWHM += fwhm;
+                        numFWHM++;
+                    }
                 }
             }
-        }
-        if (numFWHM == 0) {
-            options->inputSeeing->data.F32[i] = NAN;
-            options->inputMask->data.PS_TYPE_VECTOR_MASK_DATA[i] = PPSTACK_MASK_PSF;
-            psLogMsg("ppStack", PS_LOG_INFO, "Unable to measure PSF FWHM for image %d --- rejected.", i);
+            if (numFWHM == 0) {
+                options->inputSeeing->data.F32[i] = NAN;
+                options->inputMask->data.PS_TYPE_VECTOR_MASK_DATA[i] = PPSTACK_MASK_PSF;
+                psLogMsg("ppStack", PS_LOG_INFO, "Unable to measure PSF FWHM for image %d --- rejected.", i);
+            } else {
+                options->inputSeeing->data.F32[i] = sumFWHM / (float)numFWHM;
+            }
         } else {
-            options->inputSeeing->data.F32[i] = sumFWHM / (float)numFWHM;
-        }
+            options->inputSeeing->data.F32[i] = pmPSFtoFWHM(psf, 0.5 * numCols, 0.5 * numRows);
+        }
+
         psStringAppend(&log, "Input %d: %f\n", i, options->inputSeeing->data.F32[i]);
     }