Comet Labs WN591 Bedienungsanleitung PDF herunterladen (Seite 45)

Help! There is a comet in my computer! 42

after we mark the comet borders, we return the image back to original prior to

measurement.

How can we find out how our software actually works? Possibly this is described in the

user manual. We can also record a good image of a comet, save it and then import it to the

comet software and try to measure this same image several times using drastic changes of

the displayed image (e.g. very overexposed, very underexposed). We should keep the

borders of the comet constant in all measurements. If the way that the image is displayed

on the screen affects the values of the measured parameters, then our comet program does

not measure the original recorded image.

To get the best out of the comet assay and avoid measurement errors, we should know

how our particular software works. There are considerable variations in the exact

procedures that different software packages use.

5.10 How do I get a good quality image out of my

comet equipment?

The system for measurement of comet parameters with image analysis has several

elements (a microscope, a camera, software), and all need to be optimally adjusted to get

the best possible quality of a recorded image. The general setup of a microscope and

possible problems with its alignment have been discussed before (see chapters

Fluorescence microscopy, page 3, and Shading, page 35). Other parameters that determine

the quality of the grabbed image are related to the settings of the camera and its control via

the computer.

The aim of camera adjustment is to get an image with no saturation and with some unused

low and high grey values (see Figure 23). There are many versions of the user interface for

adjusting settings of the camera (Figure 25). Some versions even show the histogram of

image grey values. The main settings that influence the histogram of image grey values are

contrast / brightness or gain / offset and exposure (integration) time. Contrast and gain

determine how much the signal is amplified; hence they adjust the range of used grey

values. Brightness and offset determine the general brightness of the image – the position

of the range of used grey values on the whole scale of available grey values. Exposure time

defines for how long the camera collects the light signal – longer exposure times result in

brighter images. To get to know the optimal settings of your system, you will need to

experiment a little.

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Comet Labs WN591 Bedienungsanleitung Seite 45