Multispectral imaging, or photography utilizing wavelengths other than people in everyday obvious gentle, has different purposes ranging from earth observation to forgery detection in art. For instance, titanium white and lead white, two pigments used in distinctive historic eras, look equivalent in obvious light but have distinct signatures in the UV vary. In the same way, IR imaging can expose a painting’s internal layers if the pigments employed are transparent to IR.
Devices for these a niche use is obviously very dear, so [Sean Billups] determined to transform an older model smartphone into a handheld multispectral camera, which can help him analyze performs of artwork without having breaking the lender. It uses the smartphone’s digicam alongside one another with a filter wheel attachment that enables it to capture different spectral ranges. [Sean] chose to use a Google Pixel 3a, primarily due to the fact it’s cheaply readily available, but also since it has a good image sensor and digital camera software. Modifying the camera to empower IR and UV imaging turned out to be a little bit of a problem, on the other hand.
Picture sensors are obviously sensitive to IR and UV, so cameras usually incorporate a filter to block anything at all but obvious light. To take out this filter from the Pixel’s digicam [Sean] had to heat the digicam module to soften the adhesive, diligently eliminate the lens, then glue a piece of plastic to the filter and pull it out as soon as the glue experienced set. Perfecting this course of action took a bit of demo and mistake, but the moment he managed to effect a crystal clear separation between digital camera and filter it was merely a issue of reattaching the lens, assembling the telephone and mounting the filter wheel on its again.
The 3D-printed filter wheel has slots for four distinctive filters, which can permit a wide range of IR, UV and polarized-light imaging modes. In the video embedded down below [Sean] demonstrates how the IR reflectography method can aid to reveal the underdrawing in an oil painting. The process is intended to be extendable, and [Sean] has by now been seeking at including options like IR and UV LEDs, magnifying lenses and even supplemental sensors like spectrometers.
We’ve seen a handful of multispectral imaging jobs right before this drone-mounted technique was a contestant for the 2015 Hackaday Prize, though this task has an excellent primer on UV imaging.