Can I isolate my own infrared illumination in daylight to capture only nearby objects?

Asked 3/17/2015

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I want a camera setup that sees only light from my own IR source (for example an IR LED ring) even when there is daylight coming through windows. The goal is for nearby objects to reflect my IR illumination while the background is largely rejected, somewhat like a depth camera. Is there a filter that can isolate a precise IR wavelength not normally present in sunlight, or is some other active IR approach required? Also, would a standard consumer camera work for this, or would a different type of camera be better?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

11y ago

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There is no infrared wavelength that does not appear in sunlight. You would have to apply a filter to the sunlight, and to any ambient incandescent lighting, to be able to restrict the image to whatever is illuminated by your specific IR source.

Note also that most consumer digital cameras have infrared filters in front of the sensor. However they still have a small amount of sensitivity to very near-infrared light. For example, this is the result of a 2.5-second exposure at f/4, ISO 400 on an unmodified Sony Alpha using a Hoyt R72 filter, which is opaque to visible light.

Infrared 2.5-second exposure

It is possible to remove the infrared filter from digital camera sensors which will increase the level and spectrum of infrared sensitivity. However you will probably get better results using security cameras, which often have built-in 800nm or 950nm illuminators and do not have IR-cut filters.

Originally by user27832. Source · Licensed CC BY-SA 4.0

user27832

11y ago

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Not with a simple wavelength choice alone. Sunlight contains infrared across a broad range, so there isn’t a special IR wavelength you can pick that is absent from daylight. In a room with window light, an IR-pass filter on the camera would still pass a lot of ambient IR from the sun, so it won’t isolate only your emitter.

A normal consumer camera is also limited because most have an IR-cut filter over the sensor, leaving only weak near-IR sensitivity unless the camera is modified. Dedicated security or machine-vision IR cameras are usually better suited.

If you want something Kinect-like, the practical approach is active IR with structure or timing: project a known IR pattern and use a fast IR-sensitive camera plus processing to detect only your projected signal and derive depth. Even then, direct sunlight is a major problem because it strongly floods the scene with IR and is difficult to filter out selectively.

So: no simple tunable filter will make your camera see only your IR source in daylight; an active IR depth-sensing system is the realistic route.

UniqueBot

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11y ago

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