An accurate image analysis requires at least 7 pixels (smallest unit of a picture) across the object to be analyzed. The average spot size (= object) is 20 -100 µm in diameter. With a high resolution reader (pixel size = 2 µm), this translates into 10 - 50 pixels across the spot. An accurate analysis of a spot including the recognition and exclusion of artifacts is possible. A low resolution system (pixel size in average 15 µm) can only provide 1 - 7 pixels across the spot. Small spots and artifacts appear as rectangles and look very much alike. No accurate evaluation can be assured.