For the sake of this discussion I’ll use the word “grainy” as a contrast to “smooth” and “sharp”, referring to how an infrared image looks. Graininess in your image can be the result of a variety of factors. I’ll address four factors.
First, the more sensitive your detector system is the smoother the image will appear. The less sensitive your infrared camera is the grainier it will appear. In BLOG #21 I talked about N.E.T.D. The specification N.E.T.D. (noise equivalent temperature differential) relates to the sensitivity of your detector array. In other words, an infrared camera with a 100mK detector system will have more noise than an infrared camera with a 70mK or 50mK detector system and the images will appear grainier. This would be a reason to think carefully about which camera to purchase. Infrared cameras with a lower NETD cost more, but they make for a more professional analysis and presentation. The following images were taken with Fluke infrared cameras, both of which have a 160×120 resolution. However, the first one has a 100mK detector system and the other has a 70mK detector system. Although both have a resolution of 160×120, the 70mK looks smoother.
A second factor that can affect graininess is resolution. A resolution of 120×120 will appear grainer when compared to a 160×120 resolution or compared to a 320×240 resolution. The higher the resolution, the smoother or sharper the image will appear. Why? A 120×120 resolution array has 14,400 detectors. A 320×240 array has 76,800 detectors. The more detectors you have the more detail and the smoother the image. If you are performing infrared investigations for moisture issues or building envelope issues I would not recommend a resolution less than 120×120. Why? You’ll lose too much detail and perhaps miss some important issues.
A third factor that affects the graininess is the span setting. The smaller the span, the grainier the image will be. A 5° span will be grainier than a 40°span, regardless of which infrared camera you use. The reason is that the colors or tones are compressed into a shorter space, thus not allowing for a smooth transition. Notice these two images. Both are shown in the high contrast palette. The first one has a 5° span setting. The second one has a 55° span setting. Notice how grainy the first one is.
How’s your comfort level in thermography?
(The above comments represent my opinion).
Rod Hoff / Restoration Consultants Inc
Thermography Instructor / IR camera sales
3284 Ramos Circle, Sacramento CA 95827
toll free 888-617-3266 ext 301
Provider of Fluke TiS, TiR, TiR1, Ti, Ti25, TiR27, Ti27, TiR29, Ti29, TiR32, Ti32, TiR3, and TiR4 infrared cameras.
See DEMO www.moistureview.com/demo.html