Hossein Mirzaee and  Farhad Besharati,  Tree Based Decomposition of Sunspot Images .   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    March 2007, vol. 3(3). 586 - 590
    [viewed 24 April 2024]. Available from: https://publications.waset.org/pdf/8250.