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33
The secret to a good thermal image
greater contrast, but this can lead to a noisy image for objects with different surfaces or
many temperatures.
Figure 33.9 Gray, iron, and rainbow palettes (left to right).
The isotherm is a measuring function that displays a given interval of the same apparent
temperature or radiation intensity in a color that is different from the palette. It allows you
to emphasize temperature patterns in the image (see Figure 33.10).
Figure 33.10 Foundation wall: connection between the old (left in image) and the new (right in image) parts
of the building. The isotherm highlights an area of air leakage.
33.5.3 Object parameters
As we have seen, the appearance of thermal images is dependent on the thermographer's
technique and choice of settings, and the look of saved radiometric images can be altered
by editing. However, it is also possible to change the settings that are relevant for the cal-
culation of temperatures. In practice, this means that the emissivity and reflected apparent
temperature can be altered retrospectively. If you notice that these parameters have been
set incorrectly or want to add more measurement spots, the temperature measurement
values will be calculated or recalculated according to the changes (see Figure 33.11).
Figure 33.11 Change in emissivity for a saved image. The maximum temperature is 65.0°C (149°F) for ε =
0.95 in the left image and 77.3°C (171.1°F) for ε = 0.7 in the right image.
33.6 Taking images—practical tips
The following list includes some practical tips. However, note that this is not a comprehen-
sive description of the thermal imaging procedure.
• Ensure that the camera is saving radiometric images.
• Choose an appropriate position from which to take images:
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