“…Based on the used X-ray datasets, several studies differentiated the data into two classes of patients with COVID-19 and non-COVID-19 patients [ 21 , 24 , 25 , 29 , 36 , 39 , 40 , 42 , 45 , 46 ]. In others, the database included more than two classes, e.g., viral pneumonia, bacterial pneumonia, and normal and COVID-19 cases [ 17 , 23 , 30 – 35 , 37 , 39 , 41 , 43 , 47 – 50 ].…”