Here is a SQE-generated list of undocumented stuff (taken from RT-31686):

javafx.scene.image.PixelFormat

method: public static PixelFormat createByteIndexedInstance ( int[] colors )
method: public static PixelFormat createByteIndexedPremultipliedInstance ( int[] colors )
method: public static WritablePixelFormat getByteBgraInstance ( )
method: public static WritablePixelFormat getByteBgraPreInstance ( )
method: public static PixelFormat getByteRgbInstance ( )
method: public static WritablePixelFormat getIntArgbInstance ( )
method: public static WritablePixelFormat getIntArgbPreInstance ( )
method: public Type getType ( )
method: public abstract boolean isPremultiplied ( )
method: public abstract boolean isWritable ( )

javafx.scene.image.PixelFormat.Type
class: public static final PixelFormat.Type

javafx.scene.image.WritablePixelFormat
method: public boolean isWritable ( )