public int[] getBackgroundRGB() {
            if (!backgroundSet) {
                throw new IllegalStateException(PropertyUtil.getString("PNGEncodeParam9"));
            }
            return backgroundRGB;
        }
Returns the RGB value of the suggested background color.

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

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