public int getBackgroundGray() {
            if (!backgroundSet) {
                throw new IllegalStateException(PropertyUtil.getString("PNGEncodeParam6"));
            }
            return backgroundPaletteGray;
        }
Returns the suggested gray level of the background.

<p> If the background gray level has not previously been
set, or has been unset, an
<code>IllegalStateException</code> will be thrown.

@throws IllegalStateException if the background gray level
       is not set.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java