Comet Labs WN591 Bedienungsanleitung PDF herunterladen (Seite 22)

Help! There is a comet in my computer! 19

Figure 10. The comet profile of the model comet image. Box-segmentation (A): The recorded

comet intensity is the intensity on the original (grabbed) image. The scaled background

intensity is the mean intensity in the background region (4 pixels) scaled to the height of the comet

ROI (11 pixels; the scaled background intensity from Table 1). The background-corrected

intensity is the recorded intensity minus the scaled background. The dashed line separates the

head from the tail. See Table 1 for data shown in A. Close-fitting segmentation (B): With this

segmentation, a separate profile is created for the head and the tail. The principle of calculation of

the profile is the same as in A. Grey values of the image used for calculations of the profiles are

shown in Figure 8.

3.5.5 Olive tail moment

The Olive tail moment (OTM) is the last comet parameter for us to determine. OTM is

calculated as a product of two factors: the percentage of DNA in the tail and the distance

between the intensity centroids of the head and the tail along the x-axis of the comet. We

already know the first factor, but what is an intensity centroid?

The centroid of an object is also called the centre of mass. However, in our image of the

comet, the comet has no mass! Instead of physical mass, we will use grey values as the

weights to determine the position of the intensity centroid.

We only need to determine the position of the intensity centroids along the x-axis of the

comet. We also have to do calculations for the head and the tail separately.

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Comet Labs WN591 Bedienungsanleitung Seite 22