public int getTransparentGray() {
            if (!transparencySet) {
                throw new IllegalStateException(PropertyUtil.getString("PNGEncodeParam7"));
            }
            int gray = transparency[0];
            return gray;
        }
Returns the gray value to be used to denote transparency.

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

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