diff --git a/functions/image.xml b/functions/image.xml
index 7d2273f224..707d24a3db 100644
--- a/functions/image.xml
+++ b/functions/image.xml
@@ -1727,8 +1727,16 @@ ImagePng($im);
      </note>
     </para>
     <para>
-     See also <function>ImagePNG</function>, <function>ImageGIF</function>,
-     <function>ImageWBMP</function>, <function>ImageTypes</function>.
+     <parameter>quality</parameter> is optional, and ranges from
+     0 (worst quality, smaller file) to 100 (best quality, biggest file).
+     Default is to 100.
+    </para>
+    <para>
+     See also 
+     <function>ImagePNG</function>,
+     <function>ImageGIF</function>,
+     <function>ImageWBMP</function> and
+     <function>ImageTypes</function>.
     </para>
    </refsect1>
   </refentry>