Fluorescent powder. Since the size of the fluorescent droplets in the previous section was too small, the observability of the sample photos was not sufficient, so this project added an experiment to detect the dispersed fluorescent dye (6,7-Dihydroxycoumarin-3-carboxylic acid) powder directly. The Raspberry Pi camera takes pictures as follows: The python processing result of this sample was shown in the figure (the powder is marked with a green circle), and the actual number of powders is 60, but because there are powders with too large area (more than 500μm²) in the observed area, these powders are ignored in the calculation process in this project , so the number of powders is 53 and the average area is 31.86 μm², which, as expected, is larger than the average size of the fluorescent droplets. Considering the limited performance of laboratory printers, which could not print particularly small spots, so when drawing spots in the Inkscape software, the size of the spots was appropriately increased, ranging from tens of microns to 200 microns. Comparing Inkscape's drawing with the actual printed area, it was found that the printing performance was as expected: those spots with a diameter of less than 59 μm were not printed, and there were 10 detectable spots in the selected area. Besides, due to the huge difference between the actual size and the set size of the 13th spot, it was ignored in the calculation process. Meanwhile, due to the limitation of the printer performance, the calculation of quantity error is of little significance, so it was also ignored in this section. The coordinates and size information of the remaining points are shown in the table below.