UNTIL RECENTLY, MOST BUYERS OF INFRARED IMAGING CAMERAS had to make a budgeting choice between a low-resolution 160×120-pixel camera or no camera at all, but they soon learned they missed a lot at low resolution. At a starting price of about US$25,000, professional high-resolution 320×240-pixel cameras were often too costly for anyone who was not a full-time thermographer or not working for a company that could justify buying expensive tools that might be underused. That changed in 2005 when Mikron Infrared (www.irimaging.com) introduced a line of cameras that cost less than $15,000 and used a high-performance 320×240 microbolometer detector.

To make IR cameras affordable to a wider range of users, detectors with pixel counts of 160×120 (with or without interpolation) were introduced as a low-cost alternative. However, this is one-fourth the resolution of the 320×240 detector: 76,800 pixels versus 19,200. The larger detector produces an image twice as wide and twice as high, with four times the data for a given field of view.

For the working thermographer, high resolution allows a camera to work at a much greater distance from a target without loss of temperature measurement accuracy. A target must cover at least 9 pixels on the FPA to be accurately resolved, or else the resulting temperature measurement will be compromised when the camera averages in extraneous background. The lower resolution detector interpolates a greater area between pixels and averages in temperature readings unrelated to the target. In practice, a target that is 0.25 sq inches (1.6 sq cm) can be accurately measured for temperature at a distance of 60 ft (18 m) with the 320×240 detector, while the 160×120 detector has to be at 30 ft (9 m) to ensure the same accuracy.

Resolution is even more important in infrared imaging than it is in digital photography, and everyone knows how photographers boast about the resolution of their newest digital cameras. In infrared, resolution affects temperature measurement accuracy, not just image quality. The 320×240 detector, with 76,800 temperature-measuring pixels, resolves an area smaller than a tenth of a square inch at 6 ft, while the 160×120 detector, with just 19,200 pixels, can't image anything smaller than twice that size With more background averaged into temperature readings, the readings are inherently less accurate. Likewise, the low-resolution thermal image looks like it's made of tiny little squares, no matter what the viewing size.