Three years ago I developed the DOLPi polarimetric cameras  based on the Raspberry Pi. One used an electro-optical polarization analyzer, while the other used discrete polarization filters mounted on a filter wheel. The only issue with their performance was lack of speed.  I mentioned back then that high-speed polarization imagers have been built using multiple sensors, each with its dedicated, fixed-state polarization analyzer.  I finally got around to converting a 1980s-era three-tube camera into a real-time polarimetric imager.  The full whitepaper with detailed step-by-step instructions is available for download in pdf format at:  Converting_the_JVC_KY-1900_into_a_Real-Time_Polarimetric_Imager_-_Prutchi_2018

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iPhone DOLPi Camera developed by Paul Wallace

Reader Paul Wallace contacted me to tell me about the DOLPi electro-optic polarization camera that he built for his iPhone. His ingenious solution makes use of the iPhone’s flashlight to calibrate and synchronize the control of the polarization analyzer (hacked from a welder’s mask as described in the DOLPi whitepaper).

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Andrew Gliesman sent me these pictures of his DOLPi Visor replication along with a very kind note.

…I wanted to thank you for your excellent paper on the DOLPi Polarimetric Camera.  The amount of technical detail combined with providing a solution of a real world humanitarian problem made it special to me.

I recently built a DOLPi Visor and wanted to share my alternative form-factor with you (see photos.)  With respect to the build notes, everything was spot on – I just found that I needed to clean the adhesive residue after removing a polarizer film on the LCP (perhaps this had to do with the brand – I couldn’t find the MASK brand on Amazon.)…

The point about the adhesive is interesting.  Indeed, the adhesive remains transparent after removing the polarizer film, but becomes cloudy if scratched.  I found that the best way to remove it is to loosen it with a drop of “Goof-Off” and then scraping it with a sharp razor blade.

Thanks Andrew!

DOLPi – A Low-Cost RasPi-based Polarization Camera

A polarimetric imager to detect invisible pollutants, locate landmines, identify cancerous tissues, and maybe even observe cloaked UFOs!

The polarization of light carries interesting information about our visual environment of which we are usually unaware. Some animals have evolved the capability to see polarization as a distinct characteristic of light, and rely critically on this sense for navigation and survival. For example, many fish, amphibians, arthropods, and octopuses use polarization vision as a compass for navigation, to detect water surfaces, to enhance the detection of prey and predators, and probably also as a private means to communicate among each other.

While we have used technology to expand our vision beyond the limits of our ordinary wavelength and intensity sensitivities, the unintuitive nature of polarization has slowed down the development of practical applications for polarization imaging. Polarization cameras do exist, but at over $50,000, they are mostly research curiosities that have found very few practical uses outside the lab.

The DOLPi project aims to widely open the field of polarization imaging by constructing a very low cost polarization camera that can be used to research and develop game-changing applications across a wide range of fields – spanning all the way from environmental monitoring and medical diagnostics, to security and antiterrorism applications.

The DOLPi polarization camera is based on a standard Raspberry Pi 2 single-board computer and its dedicated 5MP camera. What makes the DOLPi unique is that the camera sits behind a software-controlled electro-optic polarization modulator, allowing the capture of images through an electronic polarization analyzer. The modulator itself is hacked from two low-cost auto-darkening welding mask filters ($9 each). In spite of its simplicity, DOLPi produces very high quality polarization images.

This is a first-of-its-kind project! I am not aware of any polarization imager ever presented as an enthusiast-level DIY project, yet it holds truly awesome disruptive power for the development of brand new scientific and commercial applications!

A complete description of this project in pdf format is available at: DOLPi_Polarimetric_Camera_D_Prutchi_2015_v2

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