Three areas were randomly chosen in each image using ImageJ to obtain the average red intensity value, denoted as the R-value (Figure ). Each area was specified to have an image pixel size of 64 x 150 64 (width and height), as indicated by the yellow squares in Figure . This allowed students to easily compare the RGB color intensity in specific areas of each image. To simplify the introduction to image processing, the procedure for using ImageJ was kept as straightforward as possible. The R-values were obtained without splitting the color channels in ImageJ. Each measurement was repeated for all the standard solutions, as described in detail in the Supporting Information. Students compiled all the 155 observation data in Google Sheets or Excel