Comet Labs WN591 Bedienungsanleitung PDF herunterladen (Seite 37)

Help! There is a comet in my computer! 34

Let us now drag the slider from left to right for the image shown in Figure 19. At grey

value 0, the whole image is black (no signal). At grey value 26, the first pixels appear as

small white dots (Figure 19B) – the minimum grey value in our image is 26. At grey value

36, we can see the first pixels of our comet (Figure 19C), and at grey value 151 the whole

comet (Figure 19D). At grey value 201, we see the last black pixels on a white image

(Figure 19E) – this is the maximum grey value used in our image. So, we found out that

the range of grey values used in our image is 26 to 201, and that the signal in our comet

covers the grey value range 36 to 151.

In some software packages, the grey value of the pixel at the current position of the cursor

can be displayed on the screen (Figure 20). By moving the cursor around the image, in

particular to the very dark and the very light spots, we can roughly estimate the range of

grey values used in the image. This approach is better than not checking the image grey

values at all, but we really should find a way to consult a histogram of image grey values

for adequate evaluation of the quality of the image.

Figure 20. Examples of indicators of the pixel grey value. In some software packages, the grey

value of the pixel at the current position of the cursor is displayed under the image (A, C) or close

to the cursor (B). As we move the cursor around the image, we can get a general impression about

the grey value range used in the image. In the shown case, the background is not underexposed

(grey value 32 on A; 36 on B) and a pixel in brightest spot in the comet head has the grey value

173 (B).

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Comet Labs WN591 Bedienungsanleitung Seite 37