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).