Index: /trunk/psLib/src/imageops/psImageBackground.c
===================================================================
--- /trunk/psLib/src/imageops/psImageBackground.c	(revision 27067)
+++ /trunk/psLib/src/imageops/psImageBackground.c	(revision 27068)
@@ -53,5 +53,5 @@
         for (int x = 0; x < nx; x++) {
             if (!isfinite(image->data.F32[y][x]) ||
-                (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[iy][ix] & maskValue)) {
+                (mask && mask->data.PS_TYPE_IMAGE_MASK_DATA[y][x] & maskValue)) {
                 bad->data.U8[y][x] = 0xFF;
             }