Infrared ‘calibration’

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Mark Scott Abeln
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Infrared ‘calibration’
1 month ago

I recently got a PiNoIR infrared camera for the Raspberry Pi computer.

I did a little bit of experimentation with it, and I immediately noticed that the colors are rather inconsistent:

Since this is a standard RasPiCam with the IR filter removed, I’d assume that the processing on this camera is the same as the original camera with IR filter. The processing is surprisingly intricate considering that it only costs US$25, but it is something of a mystery since it runs on the Pi’s GPU.

The above color consistency problem, I think, can be solved by fixing the white balance.

Now it is possible to do raw processing on these images — you can set a flag on the raspistill command to append the raw data as an Exif tag.

Here is my question: assuming you can extract and process the raw data, how would you ‘calibrate’ or profile the device in order to produce pleasing images? Obviously this is not a calibration, since we are mapping invisible frequencies to a false color image, but certainly some criteria might produce more pleasing images than others. I’d like a good full-color rendering if possible, and not simply one or two bold colors (actually some of the other photos are practically colorless), and I’d like to keep some of the distinct properties of IR photography, such as turning skin tones porcelain.

For example, if no infrared light is present in the scene, then the color renderings ought to be the same as found in the regular camera. But what if significant IR is present? How would you render that? Now, it is quite possible that all three channels will have a significant IR response, but I simply don’t know.

Suppose consistency in color rendering is needed — how would your operation of the camera change?

I’m curious if anyone has thoughts regarding this.

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