Comment by nine_k | Hacker News Reader

Comment by nine_k | Hacker News Reader

Most IR cameras work with IR as heat emission. They are useful in the dark, without revealing the camera.

Most optical cameras work with reflected light, not direct emission. The source of light is usually away and at an angle; this allows for shadows, textures, etc.

I don't see why an IR camera can't work the same way as an optical camera, if reflected IR is used; IR photos under e.g. sunlight look fine enough.

Radars or lidars work with their own scanning sources of illumination: microwave, IR, or optical. I wonder if the HADAR uses its own source of IR; if it does, how different it from a LIDAR?

(All these mysteries can be solved for $29, but I'm not yet curious enough.)

https://hal.cse.msu.edu/assets/pdfs/papers/2023-nature-heat-...

Thanks! This clarifies a lot.

- They use and combine both optical and LWIR data.

- They are able to split the IR signal into emissive and reflected, and thus measure the temperature and extract small variations (texture).

- They can get higher-res images using LWIR, and thus do (more) precise ranging using a stereo pair.

- Using the spectral information + some ML models, they are able to identify materials, and paint / augment pictures using this information.

That's actually impressive.

As a note, try to avoid using IR to describe LWIR, there are many IR sub bands (NIR, SWIR, MWIR, LWIR) and your phone camera can detect at least one of them.

All IR cameras catch also reflected IR. Thats why you have to know the emissivity to calculate the true temperature.

Yeah go play with an LWIR camera of you really want to understand the spectrum. For instance, everything becomes a mirror, you can see yourself standing in front of surfaces that have better than ~5um surface finish (quite rough sheet metal and such) and clouds appear hot-ish because while they are themselves quite cold, they're reflecting LWIR from the ground, hence why overcast nights are much warmer.

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