diff --git a/scripts/process-archive.sh b/scripts/process-archive.sh
index 5dd026b5..af9db9d7 100755
--- a/scripts/process-archive.sh
+++ b/scripts/process-archive.sh
@@ -21,9 +21,6 @@ exiftool -if '$jpgfromraw' -b -jpgfromraw -w "$PREVIEW_NAME" \
 	-common_args --ext jpg -r "$ARCHIVE_ROOT" -progress
 
 
-# need to calculate this correctly...
-FACTOR=4.76
-
 SIZE=900
 
 ALGORITHM=bicubic
@@ -32,7 +29,6 @@ COMPRESSION=90
 
 PATH=$PATH:`pwd`/vips-dev-7.32.0/bin/
 
-
 # XXX use find...
 for f in "${ARCHIVE_ROOT}"/DCIM/hi-res\ \(RAW\)/*jpg ; do
 	# create preview dir if it does not already exist...
@@ -41,20 +37,22 @@ for f in "${ARCHIVE_ROOT}"/DCIM/hi-res\ \(RAW\)/*jpg ; do
 		mkdir -p "$D"
 	fi
 
-	# calculate the factor...
-	W=$(vips im_header_string width "$f")
-	H=$(vips im_header_string height "$f")
-
-	# NOTE: vips appends \r to these!!!
-	W=${W//[![:digit:]]/}
-	H=${H//[![:digit:]]/}
-
-	FACTOR=$(echo "scale = 4; if($H > $W) s = $H else s = $W ; s / $SIZE" | bc -l)
-
-	echo "($FACTOR): ${f/hi-res\ /preview }:${COMPRESSION}"
-
 	# create previews...
 	if ! [ -e "${f/hi-res\ /preview }" ] ; then
+
+		# get source size...
+		W=$(vips im_header_int width "$f")
+		H=$(vips im_header_int height "$f")
+
+		# NOTE: vips appends nasty unprintable \r's to values, so we need to clean them out...
+		W=${W//[![:digit:]]/}
+		H=${H//[![:digit:]]/}
+
+		# calculate the factor...
+		FACTOR=$(echo "scale = 4; if($H > $W) s = $H else s = $W ; s / $SIZE" | bc -l)
+
+		echo "($FACTOR): ${f/hi-res\ /preview }:${COMPRESSION}"
+
 		vips im_shrink "$f" "${f/hi-res\ /preview }:${COMPRESSION}" $FACTOR $FACTOR 2> /dev/null
 	fi
 done