How is a camera using three broad spectral bands different from a standard RGB camera?
Asked 3/22/2017
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I'm reading a paper on aerial forest surveying that says the imagery was captured with an Illunis XMV-4021C camera using three broad spectral bands: blue (450 nm), green (550 nm), and red (625 nm). I haven't found much information about that camera or what they mean by "broad spectral bands." Is this type of camera substantially different from a normal consumer RGB camera with a standard color sensor, such as a compact Canon, and if so, how does it differ spectrally?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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It does not seem to be substantially different from standard CMOS sensor other than the fact that most Illunis cameras seem to be based on CCD rather than CMOS chips. The three color bands centered on 450nm, 550nm. and 625nm are certainly similar to most Bayer masked sensors in consumer cameras.
What it does seem to be substantially different from is other devices that have been previously used for tree crown delineation via aerial photography. Previous attempts apparently used imaging devices which only image using a single spectral band camera. From this paper that appears to be the same source of the quote in the question (emphasis added):
Current tree crown delineation methods normally employ the digital-count differences between crowns and surroundings in an individual spectral band or an individual component of the image, brightness and color differences between crowns and surroundings are rarely utilized together to localize crowns.
Basically, what the paper seems to be saying is that previous attempts to do such measurements did not utilize imaging equipment that simultaneously compared brightness differences and color differences.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
9y ago
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Based on the wavelengths listed, it does not sound fundamentally different from a normal RGB camera in spectral coverage. Blue around 450 nm, green around 550 nm, and red around 625 nm are broadly similar to the three color channels captured by a typical consumer camera using a Bayer color filter array.
So in spectral terms, this appears to be a standard visible-light 3-band color image, not something exotic like narrowband multispectral or infrared capture. The phrase "broad spectral bands" usually just means each channel covers a range of wavelengths around those center values, rather than a very narrow slice.
The main distinction mentioned in the answers is not that it differs strongly from consumer RGB cameras, but that it differs from some earlier tree-crown studies that used only a single spectral band. In that context, a 3-band camera provides more information for separating tree crowns from surroundings.
The specific sensor technology may also differ: Illunis cameras were noted as often being CCD-based rather than CMOS-based. But that is a sensor implementation difference, not a major change to the basic blue/green/red spectral concept.
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