User's Manual

The secret to a good thermal image33
Photography Thermography
Aesthetically pleasing Clear heat patterns
Emotive Objective
Image detail Image detail
Focus Focus
Lighting Emission and reflection
Brightness Brightness
Contrast Contrast
As with photography, in thermography there are countless possibilities for editing images
—provided they are saved as radiometric images. However, not all settings can be
changed, and not all image errors can be corrected.
33.4 The three unchangeables—the basis for a good image
33.4.1 Focus
A professional thermal image is always focused and sharp, and the object and heat pat-
tern must be clear and easy to recognize.
Figure 33.1 Only hazy “patches of heat” can be seen in the unfocused image (left). The focused image
(right) clearly shows which object is being observed and where the object is warm.
A blurred image not only comes across as unprofessional and makes it harder to identify
the object and any faults (see Figure 33.1) but can also lead to measurement errors (see
Figure 33.2), which are more serious the smaller the measurement object. Even if all oth-
er parameters are set correctly, the measurement values from an unfocused thermal im-
age are highly likely to be incorrect.
Figure 33.2 Focused thermal image (left) with a maximum temperature of T
max
= 89.7°C (193.5°F) and an
unfocused thermal image (right) with a maximum temperature of T
max
= 73.7°C (164.7°F).
Of course, the size of the detector matrix also plays a role in image quality. Images taken
by cameras with small detectors (i.e., with fewer pixels) are more blurred or “grainier”
and give the impression that they are not focused (see Figure 33.3). It should also be
noted that not every camera can be focused, and in this case the only means of focusing
the camera is by changing the distance from the object.
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