public void setPaletteHistogram(int[] paletteHistogram) {
        this.paletteHistogram = (int[])(paletteHistogram.clone());
        paletteHistogramSet = true;
    }
Sets the palette histogram to be stored with this image.
The histogram consists of an array of integers, one per
palette entry.

<p> The 'hIST' chunk will encode this information.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java