THERMAL IMAGING & VISION SYSTEMS FEATURE
PALETTES AND ISOTHERMS Palettes represent intervals with the same apparent temperatures using different sets of colours. In other words, they translate specific radiation intensities into colours that are specific to a particular palette. Frequently used palettes include the grey, iron, and rainbow palettes (Figure 6). Grey tones are particularly suited to resolving
Figure 7a Figure 7b
Figure 6: Examples of grey (left), iron (middle) and raindow (right) pallettes
Figure 8a Figure 8b
small geometric details but are less suited to displaying small differences in temperature. The iron palette is very intuitive and also easy to understand for those without much experience in thermography. It offers a good balance between geometric and thermal resolution. The rainbow palette is more colourful and alternates between light and dark colours. This results in greater contrast but can lead to a noisy image for objects with different surfaces or many temperatures. The isotherm is a measuring function that displays a given interval of the same apparent temperature or radiation intensity in a colour that is different from the palette. It allows you to emphasise temperature patterns (Figure 7).
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 calculation 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 8).
CONCLUSION Taking a good thermal image does not require any magic tricks - solid craft and sound work is all that is required. Many of the points mentioned may seem trivial. Of course, better equipment makes it easier to ensure sharp images. High-definition cameras allow the fast localisation of even small anomalies, and without focusing capabilities it is always difficult to capture a sharp image. However, high-end cameras are no guarantee of good images if used incorrectly. The basis for good, professional work is education and training in thermography, exchange of knowledge with other thermographers, and of course, practical experience.
FLIR Systems
www.flir.com
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www.kemo.com INSTRUMENTATION | APRIL 2018 17
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