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Blog #036 – Your THERMOGRAPHY COMFORT LEVEL – Why do my images look so grainy?

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.

Taken with Fluke TiR with a 100mK detector system.  Resolution is 160x120

Taken with Fluke TiR with a 100mK detector system. Resolution is 160x120

Taken with Fluke TiR1.  70mK detector. 160x120 resolution.

Taken with Fluke TiR1. 70mK detector. 160x120 resolution.

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.

5 degree span.  High contrast palette.

5 degree span. High contrast palette.

55 degree span.  High contrast palette

55 degree span. High contrast palette

A fourth factor that affects the grainiess is your selection of palettes.  Both of the images below have a span setting of 5° and yet the first one is much grainier.  Notice the variety of colors in the span bar of the first image (high contrast palette) and how often the colors change in that short span.  With a 5° span you will have a different color for every ½ ° of temperature change.  In the second image (ironbow palette) you can see a smooth transition of 4 colors over the 5° span.   It is less grainy but it is harder to pick up some of the details that you see in the first image, the vertical framework for example.
high contrast 5 degree span

high contrast palette. 5 degree span

ironbow palette. 5 degree span

ironbow palette. 5 degree span

For professional use, my recommendation is to buy the highest resolution infrared camera and the lowest NETD that you can afford.  I use the Fluke Ti32.  It has a 320×240 resolution and a 50mK detector system.  Once you have selected your IR camera, practice with various span settings and palettes

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
fax 916-736-1134

Provider of Fluke TiS, TiR, TiR1, Ti, Ti25, TiR27, Ti27, TiR29, Ti29, TiR32, Ti32, TiR3, and TiR4 infrared cameras.


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About infrarod

Rod Hoff is a Thermographer and instructor with Restoration Consultants, Inc. He teaches a two-day IR class in moisture and building envelope investigations. A graduate from Florida State University, with a degree in education, he received his formal training in Thermography from Snell Infrared and Restoration Consultants, Inc.
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