Image of shell galaxy NGC 4993 (based on the HST/ACS data in the F814W filter). Left: image processed by intensity scaling to show the outer shells. The blue line indicates the visually determined major photometric axis. The orange cross denotes the center of the galaxy. The green circles on the blue line mark the positions of the measurements of shell radii (Table 1). Right: image processed by minimum masking technique (Bílek et al. 2016), with the filter size of 1.2″, reveals the shells close to the galaxy center. We note the two-arm spiral-like morphology of the shells.