public void unsetBitDepth() {
        bitDepthSet = false;
    }
Suppresses the setting of the bit depth of a grayscale image.
The depth of the encoded image will be inferred from the source
image bit depth, rounded up to the next power of 2 between 1
and 16.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java