The successive steps of the image analysis.

<p>(a) Two of the original pictures of a population of Collembola <i>Folsomia candida</i> raised on humid plaster of Paris darkened with Indian ink. (b) The constructed still background picture. Each pixel is calculated as the darker pixel of the original set of pictures. (c) Subtracting (b) from (a) removes the still background and reveals the springtails. The white grain in the background (see arrow) has disappeared. (d) After thresholding it becomes possible to count and measure the springtails with great confidence.