Not just that, but it would presumably be sensitive to light emission spectra too. As inks can only reflect wavelengths of light that hit them, if the emission spectra has spikes or gaps - think LED or florescent - the reflected spectra will be a function of the light source[1].

Perhaps there's some accounting for this, and I'm curious to learn what it is, because it's a phenomenally complex problem.

1. You might think the sun is a standard source, but it's usually modulated by the atmosphere[2].

2. Unless you are in space.

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aDyslecticCrow 3 days ago | parent | next [-]

> Perhaps there's some accounting for this, and I'm curious to learn what it is

The slip itself is a calibration reference, so a clean photo of it could serve to compensate for the lamp and camera and calculate how accurate the readings is for different parts of the spectrum. (But good wide spectrum light would be ideal for high precision readout)

You're also still limited to visible light because of the camera uv and ir filter, for which the sun is a decent reference.

	▲	kelseyfrog 3 days ago \| parent [-]
		oh, yes of course! Thank you :)

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voidUpdate 3 days ago | parent | prev [-]

I don't think the sun is even a perfect source when you're in space, doesn't it have gaps in its emission spectra from the gasses that make it up?

	▲	actionfromafar 3 days ago \| parent [-]
		You are quite right, I had no idea. "Between around 10,000 nm (far infrared) and around 100 nm (deep ultraviolet), the spectrum of the Sun's spectral irradiance agrees reasonably well (though not perfectly) with that of a blackbody radiator at about 5,700K. That is about the temperature of the Sun's photosphere. The deviation from a perfect blackbody spectrum is due to many factors, including the absorption of light by constituents of the solar atmosphere, and the fact that the photosphere is not uniform, but has some hotter and some cooler regions, so that what is seen from the Earth is a composite spectrum of blackbody radiators at a range of different temperatures. About 99% of the total electromagnetic radiation coming from the Sun is in the ultraviolet-visible-infrared region." https://acd-ext.gsfc.nasa.gov/anonftp/acd/daac_ozone/Lecture...