Auto Image is a feature found on many modern thermal imagers. While this feature may be helpful in certain imaging situations, its usage can cause thermographers to overlook significant thermal anomalies.
Humans have come to rely on technology to make our lives easier. We frequently take for granted how many mundane chores of the past have been automated. Each day we rely upon automatic transmissions in our cars, auto correction in word processors, and auto flush in lavatories. As infrared imaging has matured, automatic image adjustment has become a common feature on thermal imagers.
Auto Image, also known as auto adjust, is a feature commonly found on today’s thermal imagers. When engaged, the thermal imager will automatically adjust Level and Gain values so that the coldest and hottest objects within the imaged scene will be set as the lowest and highest temperature limits respectively. Auto Image may be for a single frame or it may allow for constant adjustments to automatically take place in real time.
While single-frame auto image may provide a good starting point for level and gain settings, full time usage of auto image will cause level and gain values to constantly change as the imager is panned across a given target. With values constantly changing, it is nearly impossible to make comparisons between imaged objects since there is no fixed, baseline value. In addition to making thermal imaging confusing, the use of fulltime auto image will cause many thermal anomalies to go undetected.
Thermographers who own thermal imaging equipment should familiarize themselves with their equipment to determine if their imager features automatic image mode(s). For imagers featuring single frame auto, a thermographer may use this feature to allow the imager to ‘suggest’ initial level and gain settings. For scenes that do not have a wide variation in temperature such as building envelopes or roofs, auto image may provide optimal imagery. If not, the thermographer should then manually adjust the imager’s level and gain settings in order to optimize the displayed image.
For thermal imagers that do not have onboard level and gain controls or for those that feature full-time auto image, the technique for optimizing the displayed image is as follows:
- Set imager to Auto Image mode
- Aim and focus imager on item of interest
- Pan imager slightly to obtain optimal contrast within scene
- Immediately switch to Manual mode to lock range/level settings
- If possible, adjust range and level controls to further optimize displayed image
ith the above steps completed, the thermographer may continue imaging similar objects under similar conditions. Should scene conditions change, the above steps may be repeated as necessary.
Properly adjusting level and gain is an extremely important part of thermal imaging. For best results, a thermographer should never rely on full time auto image to provide optimal imagery.