2.3. Microscope and image capture
A ZEISS Apotome 2 microscope (Zeiss, Heidenheim, Germany) was used to take pictures of different samples on the haemocytometer with the same parameters (bright field, 20x objective lens, 27.36 msec exposure time). Due to the limited field of view in microscope imagery, each picture included 120 counting chambers. For ease of observation, the images were processed, and the 16 smallest counting chambers are displayed in Figure 1A and Supplementary Figure (Fig.SA), with or without a complex background. As a result, a total of 72 images were collected from the two groups (36 with simple backgrounds and 36 with complex backgrounds).