Comet Labs WN591 Manual de usuario descargar pdf (Pagina 29)

Help! There is a comet in my computer! 26

5 Image acquisition

The first rule of image analysis states that all care should be taken to record images of the

highest quality possible. Information that is not contained in the grabbed (recorded)

image cannot be restored later, no matter how we change and process our image.

An image analysis system has many settings that affect the properties (quality) of the

grabbed image. It is extremely important to make sure that all settings are optimal for

recording of the comet images. Incorrect settings for image acquisition can invalidate

the linear relationship between the intensity of light emitted from the comet slide and

the grey values on the recorded image! This results in inaccurate measurement of the

comet parameters. The main principle of image acquisition is this: The image for

measurement of the comet parameters must contain as much information as possible.

How do we achieve this?

Our measurement of the comet parameters extracts quantitative information (numerical

parameters) from an image. The more information the image contains, the more precise our

measurement is. Let us say that we were careless when we were recording a comet image

and we did not optimally adjust all settings that define image quality. So we grabbed a

completely black image – the grey value of all pixels is 0 (Figure 15A). This image

contains no information at all – we do not even know if there was a comet under a

microscope or not. Now we try to grab a better image, and we adjust some settings. This

time we have more “luck” – we can still hardly detect the comet, but at least we see that

there is one (Figure 15B). Then we record a very good image – now we can see many

different shades of grey in the comet head and tail (Figure 15C). This image contains

sufficient information for accurate measurement of the comet parameters. Or, at least, this

is what it looks like to our eyes.

Figure 15. Effects of image acquisition settings on the information contained in an image of a

comet. A black image contains no information (A). Image B contains more information than image

A, but does not show all details of the comet. Image C contains the most information of the three

images.

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Comet Labs WN591 Manual de usuario Pagina 29