The focus of the thermal camera: one of the most important moments of the evaluation.

The focus of the thermal camera: one of the most important moments of the evaluation.

22/03/2023 Home

One of the most common mistakes in thermography is not properly focusing on the subject during the thermography evaluation. In this article, we will see what factors are key to correcting it.

Thermography is a non-invasive technique that uses infrared cameras to capture the thermal radiation emitted by an object or a surface, in our case the skin surface of athletes or patients with a good focus on the body. These images show the temperature distribution across the object, which can reveal valuable information about its state and physiology.

To do this, there are several factors that we must consider so that the image is correctly analyzed, and we get the most out of the thermographic evaluation:

  • The first of the factors is the number of pixels that the image has, this will depend on the quality of the camera, better cameras will have a higher resolution allowing more information from each area to appear in the focus.
  • The second factor is the subject’s position; the better framed it is in the focus, the better optimization of the regions we will have.
  • Finally, the third point is sharpness, or what we understand as a focused photo. If we have a correct focus, we should see the outer edges of the extremities in the thermographic photograph.

How to get the right focus with the camera

From ThermoHuman we have made this tutorial to explain what the key points are to make a sharp focus on the person.

As can be seen in the video, the intention is to make the edge of the extremities as clear as possible, with the aim that the information contained in the pixels enters the segmentation of the body regions in an optimal way.

To make sure, look at the outline of the person, if there is a green aura, it means that the focus is in another area (it may be in the background). If this is the case, try pressing the focus button again while aiming at the knee or turn the focus wheel on the lens to sharpen the edge. If you want to go deeper into the subject, click here.

What happens if the camera focus is not correct.

As seen in previous posts, if the focus is not correct, certain problems may appear with the analysis of the image. From the fact that it cannot be analyzed to a bias in the data due to the error of the approach.

Next, we share the analysis again according to the type of approach:

Focus correct
Figure 1: Comparison of approaches: (a) wrong approach, very fuzzy contour; (b) incorrect focus, diffuse contour, the product of having focused on the background; (c) correct focus, the subject differentiated from the background, with a well-defined outline. Only the latter allows us to make an optimal qualitative and quantitative analysis, extracting quality thermal information and drawing effective conclusions.

The first image shows an example of a close focus (around 30cm, but the person is 2.5m away). The result is a blurry image. As you can see in Figure 6, this image cannot even be analyzed.

The second image shows an example of focusing on the background (about 3m, but the person is 2.5m away). The result is an image with a slight green aura around the outline because the focus is on the wall behind the person.

The third image shows an example of correct focus on the skin surface (around 2.5m, the same distance as the person at 2.5m). The result is a clear image that perfectly distinguishes the profile.

For the best focus, follow the instructions in the video to sharpen the edge.

Europa Thermohuman ThermoHuman has had the support of the Funds of the European Union and the Community of Madrid through the Operational Programme on Youth Employment. Likewise, ThermoHuman within the framework of the Export Initiation Program of ICEX NEXT, had the support of ICEX and the co-financing of the European Regional Development Fund (ERDF).

CDTI Thermohuman has received funding from the Centre for the Development of Industrial Technology (CDTI), in participation with the European Regional Development Fund (ERDF), for the R+D activities involved in creating a new tool, based on thermography, for the prediction and prevention of rheumatoid arthritis. See project detail.