Index: trunk/ppImage/src/ppImageReplaceBackground.c
===================================================================
--- trunk/ppImage/src/ppImageReplaceBackground.c	(revision 26895)
+++ trunk/ppImage/src/ppImageReplaceBackground.c	(revision 41382)
@@ -144,6 +144,16 @@
     for (int y = 0; y < numRows; y++) {
         for (int x = 0; x < numCols; x++) {
-            if (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskVal) {
-                image->data.F32[y][x] = 0.0;
+            if(options->doApplyPixelZero) {
+              if (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskVal) {
+                  image->data.F32[y][x] = 0.0;
+              } else {
+		float value = backData[y][x];
+		if (!isfinite(value)) {
+		    image->data.F32[y][x] = NAN;
+		    mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] |= options->lowMask;
+		} else {
+		    image->data.F32[y][x] -= value;
+		}
+  	      }
             } else {
 		float value = backData[y][x];
@@ -154,5 +164,5 @@
 		    image->data.F32[y][x] -= value;
 		}
-	    }
+            }
         }
     }
@@ -162,6 +172,16 @@
     for (int y = 0; y < numRows; y++) {
         for (int x = 0; x < numCols; x++) {
-            if (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskVal) {
-                image->data.F32[y][x] = 0.0;
+            if(options->doApplyPixelZero) {
+              if (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskVal) {
+                  image->data.F32[y][x] = 0.0;
+              } else {
+                float value = psImageUnbinPixel(x + 0.5, y + 0.5, modelRO->image, binning); // Background value
+                if (!isfinite(value)) {
+                    image->data.F32[y][x] = NAN;
+                    mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] |= options->lowMask;
+                } else {
+                    image->data.F32[y][x] -= value;
+                }
+              }
             } else {
                 float value = psImageUnbinPixel(x + 0.5, y + 0.5, modelRO->image, binning); // Background value