A Thermographer is like a professional photographer – both communicate a message about their subjects through imagery. Similar to photography, focus, composition, and exposure of thermograms are important since they are often the main vehicle that a Thermographer uses to convey information.
The following tips will help ensure the quality of thermal images:
- Ensure that the image is in focus. High pixel count imagers are still “low resolution” compared to even the lowest cost daylight cameras. Typical infrared images may not seem very “clear” to an end user who has no experience interpreting thermograms. Capturing images which are even slightly out of focus will degrade their clarity and can compromise the accuracy of radiometric data embedded within the thermogram.
- Show your target as large as safely practical. Ideally, the target should fill up a significant portion of the imager’s display screen. Select an imaging distance and lens to ensure that the target is big and clear in the imager’s viewfinder. By using the maximum amount of pixels across the target, you provide the best optical and thermal resolution and minimize measurement errors due to spot size limitations.
- Adjust imager Level and Gain settings to provide the most dynamic range of color for the object. Adjust the imager to use most of the color on the object and limit how much color is used for the background unless it is important to also show some background information. This approach will give images the best contrast while conveying the most thermographic information to the recipient of the report.
There are many philosophies on how to best thermally tune images and one may be more appropriate than another depending on the application and what the Thermographer is trying to show the end user. One approach is to treat tuning as a dynamic element, tuning for each image taken. Another is to tune all images the same so a large set of images all have the same temperature span which makes them easier to compare when viewed as a set.
For instance, if a specific exception within a structure’s wall is the target, tuning the image to best show that local area of interest may be appropriate. An example of this would be to tune the image so that the details of an insulation void within a wall, or a thermal bridging element are well defined using the most amount of colors across the smallest temperature span to clearly illustrate the exception. However, if the task is to image a side of an entire building then you may choose to sacrifice some local thermal contrast to achieve a more uniform presentation down the length of a building wall by tuning all images to the same span and level.
For a comprehensive report of a building you may need both globally tuned lower dynamic range images taken sequentially down the side of a building and high dynamic images of specific areas on that wall which have been finely tuned to best show that particular exception.
In electrical work, each image is typically tuned for a specific target. In this application, it is critical to finely tune the image such that it is possible to see from where heat is being generated in a group of connections or components.
The job of the Thermographer is to locate exceptions and present them to the end user through report imagery. Images which are clearly focused, well-composed, and properly tuned will convey the most information and require the least amount of explanation.
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