The contrast of speckle images using viscous fluid flows Wafaa E. Ali, A. M. Hamed, H. El-Ghandoor, J. El-Azab and A. Samir Eur. Phys. J. Plus, 138 5 (2023) 477 Published online: 29 May 2023 DOI: 10.1140/epjp/s13360-023-04112-z