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Inspired by the single pixel digital camera (see link). Instead of focusing the light on a regular single pixel color sensor, you could put the incoming light through a rotating prism that separates the spectrum of the incoming light and measure the strength everywhere in the spectrum.
The resulting
photo would tell you so much more about the nature of what you've taken a photo of then a regular color shot. To an extent, you would know the chemical makeup of what the photo was taken of, especially if the subject was illuminated by broad spectrum black body radiation.
Another thing you could add is a rotating polariod filter, to determine polarization. This might tell you something about reflections in your photos.
Single pixel digital camera
http://www.physorg.com/news79019816.html
[jmvw, Nov 01 2006]
[link]
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So is this a single pixel spectral camera or a regular CCD array spectral camera? |
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You could use a set of parallel, rotatable, elongate prisms over the top of the CCD array to separate the spectrum to each pixel. |
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You may not be able to do proper spectral analysis because of attenuation of various frequencies of the lens system. |
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I don't think anything as complex as a
rotating prism is required. Most digital
cameras already interpolate the image.
An 8 megapixel camera will typically
have 4 million red (er wait... no... green)
pixels, 2 million red
and 2 million blue. The camera's
firmware will spit out 8 million RGB
pixels. |
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If you want to spinning prisms and
twirling polarisers, all you need to do is
increase the diversity of the pixels --
that one is broad spectrum red with 60°
polarisation. That one is narrow blue
around the colbalt line with no
polarising filter. |
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[+] because I would to have a camera
that sees things I can't. (as xaviergisz
says, though, current lenses are
designed to correctly focus and
transmit only visible light.) |
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//So is this a single pixel spectral camera or a regular CCD array spectral camera? // |
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It's a single pixel spectral camera. The singular location of the sensor should make it easier to build accurate optics for wavelength selection. |
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I think NASA would have liked this camera on the Mars rovers, instead of those filters. |
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Those are terrific photos, Ian. |
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What would be the equivalent of a flash? |
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[st3f]//Most digital cameras already interpolate the image// So, extrapolate the image from the blurred colour from a single pixel by deconvolution? |
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//What would be the equivalent of a flash?// |
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You'd want a true full spectrum flash. I believe black body radiation is broad spectrum and a thermal flash such as a magnesium flash might do well. Incandescent light would work well too, if the filament is hot enough to get into the ultraviolet. The old single use flash bulbs might work great. The camera could compensate for a somewhat uneven spectrum of these lights. A regular xenon flash could be used, but the spectrum would be limited to the lines of the gas and you would end up with little more then a good old color photo. |
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//as xaviergisz says, though, current lenses are designed to correctly focus and transmit only visible light.// |
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Regular camera's do excellently in near infrared which is commonly used for spectrophotometry. Digital camera's have a filter glued to the CCD to filter out IR. Some people replace this filter with a piece of dark (exposed and developed) color negative film to make digital IR camera's. Considering that UV filters are common, I think camera optics may work in near UV too. |
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I doubt that focus of a quality lens is very dependent on wavelength. If it were you would have some color shift even in visible light. Ian's crisp IR photos also illustrate the same focusing in in visible and IR. When he took these photos, he focused using visible light. |
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Note that this camera wouldn't necessarily range to IR and UV. The important part is that it records a detailed spectrum rather then some broad ranges. |
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Dub: I was asssuming that the camera
would have more than one pixel. I'm
bewildered why the idea is restricted to
that when so much more is possible. |
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st3f, please follow the link about the single pixel digital camera. It's a recently developed, different way of producing a full image. |
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As I understand it, it uses a randomly oriented array of tiny mirrors to reflect light from a variety of angles onto a single pixel light sensor. It takes a number of samples with the mirrors re-oriented randomly each time and software reconstructs the only image that would have produced this combination of samples. |
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I was hoping this might be good for photos of ghosts. |
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You couldn't use a flash for a spectral camera since exposure time would be at least a few seconds to do a spectral sweep. |
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[jmvw] I love the idea of a black flash! :)
Put on the kettle- Fill the cube - I'm going to take a picture. |
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st3f: I was half-baking... Wondering, if the blur is made up of convolved image data, why you couldn't deconvolve it to re-create the scene - Using 1 pixel's cool, because, presumably, there's no need to be so careful about the RGB quality of that sigle pixel (when you have a vast array of 'em, it's quite important that they all behave the (roughly) same, I guess) -
As all the pixels would be re-generated from the same (possiblly, RGB-wise, skewed) pixel, and that could be corrected after the image had been re-created... BTW most of this might be b0llux :) |
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I like it! Even though I thought, when I clicked on it, you were suggesting taking pictures of ghosts. That'd be cool, too. But I think your system would be hard to make, and it would be hard for the average viewer to know what the heck you picture is. NASA WOULD love it!! I like my normal camera, though. It's simple. |
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[+] I want a DC to X-ray camera - It should compress all the frequencies (non-linearly, throughout the whole spectrum) to just those we can usually see.
What would I do with it? Dunno, yet - But I want one. |
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Hyperspectral imaging is baked, WKTE, and used in space
for decades. A
hyperspectral camera that captures the whole cube
(width×height×wavelength) at once was even proposed in
1938,
according to Wikipedia. |
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I guess the novelty here is just to make a hyperspectral
camera
using the DMD coded-aperture technique (which replaces
the
spatial sensor used in most cameras with a global sensor
and a
spatial modulator). That would make some aspects of
building a
hyperspectral camera easier for less-sophisticated
builders (such as
amateurs) versus other types of hyperspectral camera, so
[+]. |
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I happen to have a DMD with some stuck mirrors. Maybe
I'll see if I can get
that working someday. |
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I once built a coded aperture spectral camera, with a mask I made from orthographic film (took some pictures of aperture patterns, then developed it, used the negative as a mask). It didn't work that well, the silver wasn't high enough contrast. |
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The reconstruction was done in matlab, but I suppose a modern smartphone would be able to do it. I'm not convinced there is a market for consumer spectral imaging though. |
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