another try...

tools/motionblur.sh

@@ -13,7 +13,7 @@ set -e   ;   set -u
 source tools/config.sh
 source tools/fonctions.sh
 
-START=50
+START=1
 if [ $# == 1 ]
 then
 	START=$1
@@ -32,9 +32,10 @@ do
 	imgB=$(printf "frames/Spool/%05d.png" $((frame-1)))
 	imgC=$(printf "frames/TMP/%05d.png" $frame)
 	# echo $imgA $imgB
-	printf "%d " $frame 
+	printf "%8d" $frame 
 	composite	$imgA   $imgB			\
-			-blend  70%			\
+			-blend  50%			\
+			-blur 1x1			\
 			$imgC
 done