Wednesday, February 9, 2011
Some infrared cameras do not have the ability to manually adjust the Level and Span, which is the equivalent of brightness and contrast. This can often be accomplished with image processing software after the image has been captured and saved. However, anomalies can go undetected in the field if the level and span are not adjusted well. If no problem is detected in the field, the image will probably not be saved for further analysis.
The FLIR i3, i5, and i7 cameras can be set to “Auto” or “Lock.” In the Auto mode the camera will continuously adjust the level and span. The adjustments depend upon the apparent temperatures in the scene. If there is something very cold in the image, such as the clear sky, the camera will increase the span by decreasing the low end of the temperature span. If there is something very hot, the camera will increase the span by increasing the high end of the temperature span. Whenever the span is increased the contrast is decreased. The span adjustment should be based on your target of interest, or a specific part of your target of interest, not necessarily the entire scene.
Many thermographers using the i series cameras are trying to detect relatively small temperature differences due to lack of insulation, air infiltration, or moisture. If there is a hot or cold object in the scene, the auto mode often sets the span too high and the contrast is too low for easy detection of the anomalies they are seeking. There is a way to use the features on these cameras to get the best possible results.
Consider this image, captured with a FLIR i7:
This is an exterior wall taken inside a building when the outside temperature was about 19°F. A hot cup of water was placed in the scene to simulate a hot transformer or baseboard heating system. Notice that the “Auto” adjust set the temperature span from 52°F to 132°F. This is a span of 92°F. If the “Lock” mode was selected at this time, it would simply lock the temperature scale at this setting. Since we are interested in thermal patterns on the wall, we certainly do not need the high end of the scale at 132°F.
Wednesday, February 2, 2011
The new up to date book “Infrared thermal imaging – fundamentals, research and applications” by Michael Vollmer and Klaus-Peter Möllmann from the University of Applied Sciences in Brandenburg / Germany gives a straightforward introduction to thermography.
The hard cover book is in full color with about 600 pages and more than 600 images. It may either serve as textbook for beginners or as handbook for expert practitioners such that it may become an ultimate resource for every user of thermography.
Due to the modular structure, readers can start studying whatever they like, be it the theoretical background of cameras, detectors, thermal radiation and heat transfer or be it for example applications for building science, detection of gases and the study of micro systems. A multitude of other applications is also included such as electrical and miscellaneous industrial applications (metal, car, aircraft), medical and veterinary studies, the use in sports and arts as well as surveillance and fascinating investigations in nature.
published in the US : October 2010, available from Wiley for 170.- US $ (or 204.- CD $)
or to be ordered from any bookstore like Amazon etc