Comet Labs WN591 Manual de usuario descargar pdf (Pagina 13)

Help! There is a comet in my computer! 10

Figure 4. Information on an image is coded as grey values. An image of a comet is composed of

separate pixels (A), where each pixel has a grey value, as shown in B for the small image area

outlined in red in A. The model image is an 8-bit image with available grey values 0-255. The

relationship between the grey value of a pixel on the image and light intensity that a camera

element detects (emitted from DNA present in one small dot in the comet) is linear (C).

3.2 Segmentation

Next we need to determine which parts of the image represent the objects that we wish to

measure. This step of image analysis is called segmentation, and the regions of the image

that are measured are called regions of interest or ROI. With segmentation, our image is

divided into segments: objects (ROI) and background (all area outside ROIs).

For measurement of the comet parameters, we need to define two regions of interest in the

image: the head and the tail. There are several ways to define ROIs. We can draw boxes

around the regions, as shown in Figure 5A (box segmentation). Some comet software

packages can do a closer fitting of the head and the tail region using more sophisticated

(semi-)automatic detection of the head and the tail (Figure 5B; close-fitting segmentation).

100

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250

Grey values

Amount of DNA

Intensity of emitted light

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100

150

200

250

Grey values

Amount of DNA

Intensity of emitted light

240 221

221

46 41

240 221

221

46 41

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Comet Labs WN591 Manual de usuario Pagina 13