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People have done it for a variety of purposes (natural image statistics, astronomy, etc). I can post references later. Problem is that it almost universally req
by daniel_reetz 14y ago
People have done it for a variety of purposes (natural image statistics, astronomy, etc). I can post references later. Problem is that it almost universally requires you to photograph a standard light source or a standard reflectance target under a standard illuminator. Or a monochromator. So you can calibrate your cheapy device but you need an expensive/scarce standard.
It's an interesting problem and I look forward to seeing how they solve it.
- eternauta3k 14y ago> requires you to photograph a standard light source How about a black body? Tungsten lamp perhaps?
- nmz787 14y agoYou want a "peaky" light source to build the spectral response model, xenon or deuterium flashbulbs are cheap on amazon... I would lean towards using deuterium because I think the relative power of the peak to the blackbody floor (the rest of the light freqs) is less than the xenon, so you'd have less chance of the peaks dominating your sample with a less sensitive webcam type sensor
- tomkinstinch 14y agoBack in the day, standard illuminants were candles made from spermaceti--the wax substance from the cavity of a sperm whale (it was also used as space-grade lubricant until very recently). Nowadays, CIE Illuminant D represents a sort of model of natural daylight. I bet a blue sky sunny day could be used for calibration, if the instrument is pointed straight up and a function corrects for lon/lat and time of the year. For reflectance measurements, the highly-lambertian Spectralon material is basically just well-controlled Teflon sheet. Some PTFE sheet from McMaster might do the job for DIY purposes.
- sp332 14y agoSunlight is tricky because colors can be distorted according to the angle of the light through the atmosphere, hazing, dust, etc.
- tomkinstinch 14y agoCertainly, but you could account for much of it--and average away the rest.