diff --git a/make-includes/standard_rules.make b/make-includes/standard_rules.make
index b9fdb3f..86df9ab 100755
--- a/make-includes/standard_rules.make
+++ b/make-includes/standard_rules.make
@@ -61,11 +61,17 @@
 %.html: %-derived.xml
 	$(call xslt,$<,xml2html.xsl,$(call xslt_parameter,paper,$(PAPER_NUMBER))) > $@
 #
-# PNG from TIFF.
+# PNG from TIFF (normal)
 #
 %.png %-print.png %-web.png: %.tif
 	convert "$<" $(IMGDIR)/$@
 #
+# PNG from TIFF (slide background)
+#
+%-BG.png: %.tif
+	convert -blur 0.5 $< $(IMGDIR)/$*.png
+	convert $(IMGDIR)/$*.png -threshold 0,0 - | composite -dissolve 25% $(IMGDIR)/$*.png - $(IMGDIR)/$@
+#
 # PNG from PICT.
 #
 %.png %-print.png %-web.png: %.pict