Instantiating the Invisible

Instantiating the Invisible

My initial intent for this post was to elaborate on a concept that I found inspiring. Jörn Loviscach (http://www.j3l7h.de/about.html) had posted a demonstration of a “Poor Man’s Thermographic Camera” that consisted of low cost parts. It scans a scene and processes the visual data to create a thermographic image. The thermo cam consists of a pyrometer sensor (aka non contact ir thermometer), two servos that tilt mirrors, and mounting hardware. It acquires images from the reflection of heat by tilting “mirrors” and redirecting the heat source to the sensor. More importantly, it then applies filtering to the field sweeps. These motion blur filters clear out the noise. Lastly, the field scans are done horizontal and vertical with the filter results from each combined to yield an accurate thermographic image.

Here is another example using a single pixel thermopile sensor

Not to fault the above authors for leaving out the semantics, but there was still a disappointing lack of detail in how the images were acquired, processed, and presented. As a result I set about to do the same using a Melexis MLX90621 sensor. However, I soon realized that the effort and results were not as cost effective had I just used a Lipton FLIR Module. My Melexis project was set with a $200 budget. If I doubled my budget to $400, I could achieve 10 times the quality with a Lipton sensor.

You can see an example of resolution differences and FOV between a source, Lipton, and Melexis sensor below. The FOV of each sensor is the orange square.

You can see that the Melexis would never achieve the results of the Lipton. The Lipton sensor would also require fewer samples per sweep. This resulted in me abandoning my initial intent of creating a field sweep device using the MLX90621. Instead, I’ll attempt to cover the theory behind the imaging methods used. First, lets look at the sensors.

One of the challenges with early sensors was their low angular pixel resolution. You were out of luck if you wanted to clearly see an object that was smaller than your pixel resolution. At best, the smaller object would appear as a shaded pixel. Image processing has extended the sensors data gathering ability and transformed digital imaging and data acquisition. Here is an example of the idea.

As the pixel and object align, the value in the pixel changes slightly. Although the pixel angular resolution is fixed, it’s angular position is not. The slight changes in angular position detect the value changes of the smaller object. This is the key behind a basic function of image processing.

Returning to ImageMagick, this webpage (http://www.fmwconcepts.com/imagemagick/fourier_transforms/fourier.html) contains some extensive details about fourier transforms. Fourier transforms are the cornerstone of the image processing methods presented on that page. In it, you will find a section titled “Motion Blur”. This technique is how we can attain details the sensor is unable to provide natively.

I can’t say definitively that this is how the “Poor Man’s Thermographic Imager” works. However, I strongly suspect this could be one possibility. Image processing is central to any imaging technology. Without it, much of our science would be speculation. It is a vast field of study. I could spend several years with weekly posts solely covering the topic.

If you have further interests in the subject material I’ve attempted to cover the past two months, please check out this course offered by Duke University, https://online.duke.edu/projects/image-video-processing/. There are more resources on the topic as well, I just can’t type endlessly.

Remembering Joe Summers

On December 11th, 2016 our family suffered a devastating loss with the passing of Joe Summers.  He was a young admirable man at the threshold of life.  The sudden and senseless tragedy is a harsh reminder how finite our stay is.  We will not be afforded with knowing what his life would have become.  All that can be done is to learn and love one another.  Taking this step forward is the most difficult without him.  His spirit lives in those that have had the joy to experience his wit, honesty, laughter, and smile.  The only comfort we can find is the sharing of that spirit through our stories and memories of this wonder son, brother, nephew, and friend.  We all carry your light in us Joe.

 

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