protected float calculateHeight(ColorRGBA color) {
        return (float) (0.299 * color.r + 0.587 * color.g + 0.114 * color.b);
    }
Get the grayscale value, or override in your own sub-classes
jme3-terrain/src/main/java/com/jme3/terrain/heightmap/ImageBasedHeightMap.java