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UltravioletPhotography

Simulating avian vision - Gallus Gallus, aka chicken


Augustinn

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Question to the group. What will be the best method of creating multi spectral image which will simulate avian vision? Reflectance and absorbance in UVA (peak 385nm) spectrum should be fairly straight forward but combining it with "enhanced" visible spectrum may be quite tricky. I attached spectral sensitivity curve of water fowl (chicken) for your reference.

post-125-0-81150600-1475001588.jpg

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First I'd need to know about the particular Bird's visual receptors.

Do they have 4? One each for UV, blue, green and red?

Or, do they have 3?

Also does the Bird see past 380 nm in to deeper UV?

 

If I recall correctly, Bird vision is Tetrachromatic. So right away we have a problem in modeling Bird vision because photographs are Trichromatic -- combining the three primaries of light and all that.

 

We do have filters which pass a lot of UV, some blue and a little bit of green. We often use those to emulate Trichromatic insect vison. Examples abound here on UVP if you click the Insect Vision tag.

 

But for Tetrachromatic vison? You would be looking for a filter which passes a lot of UV and then a little bit of blue, green and red (when used in Sunlight where the balance of IR and Visible light is hugely greater than UV light.) There might be a way to do this. (See below.) But I'm not quite sure how it would play out in a Trichromatic photograph. Something is going to get lost.

 

Here is a possibility for Tetrachromatic emulation. Make a UV photograph of the subject. Then "overlay" it as a Luminosity layer onto a Visible photograph of the subject. That would give the tonality of the UV over the colours of the Visible. (See below.) That is not really how visual receptors work for an animal which has UV as an actual colour, but this kind of overlay does at least provide a way of combining UV with R, G and B.

 


 

This photo of a flower bouquet was made with Hoya U-330 filter glass if 1.5mm thickness stacked with an IR blocker s8612 of 1.75mm thickness. The net effect is that the filter passes a lot of UV, some blue, and a little bit of green and even smaller amount of red. I suppose in some way you could say that this emulates Tetrachromatic vision. I'm not entirely sure though.

 

Nikon D600-broadband + Coastal Optics 60/4.0 + [stacked U-330(1.5mm) + fS8612(1.75mm)] in Sunlight

f/11 for 1/2.5" @ ISO-400

The key to the emulation here is the raw colours -- no white balance applied. I need the red to be present as it was recorded. Yet this is not quite right because any UV-absorbing portion of a flower should show up here as the original colour. That does not quite happen. Still, we have managed to combine some UV, R, G and B because the UV-signature pattern of the sunflower does show up. The photo could be made brighter, but I didn't want to tamper with it too much just yet.

bouquet_u330-150+s8612-175_sun_20160914wf_50878rawComppn01.jpg

 

 

Here is the visible version of the bouquet.

Nikon D600-broadband + Coastal Optics 60/4.0 + Baader UV/IR-Cut in Sunlight

f/11 for 1/800" @ ISO-400 EV-.07

bouquet_visRef_sun_20160914wf_50701pnFinal.jpg

 

 

And, of course, a UV false-colour version of the bouquet.

Nikon D600-broadband + Coastal Optics 60/4.0 + StraightEdgeU UV-Pass in Sunlight

f/11 for 2" @ ISO-400

bouquet_uvBaaderU_sun_20160914wf_50762pnWBprofCrop01.jpg

 

 

If you layer the tonality of the UV photo over the colours of the Visible photo, you get this. It might be a better Tetrachromatic emulation?

bouquet_visRef_sun_20160914wf_50701uvLumOverVis.jpg

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Here is a graphic representation of the problem of emulating insect or animal vision. I've tried to show how a golden-yellow Sunflower with a dark brown disc would appear in various forms of "vision". We run into trouble in any 3-primary vision model when we try to emulate reflected UV or reflected combined reflected red, green or blue (or any combination of those). In this little diagram I've used a mottled colour to represent reflected UV combined with reflected green or with reflected yellow.

 

VariousVisions.jpg

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Been thinking (yeah, it hurts)......do chickens have rod receptors ?

I am gathering that our (human) rod receptors give us the luminosity in our vision.

Without luminosity in our vision the world looks very plain & uninteresting, without any sharp details.

Col

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Mapping tetrachromacy into a trichromic model is indeed fascinating. Is reminds me of changing the frequencies of things we cannot hear but other animals can, like bats and elephants.

 

Seems like there should be some way to just compress the wider visual frequency range into our visible range. All our natural colors would be proportionally red shifted with UV shifted into visible. Yes, Col, head beginning to hurt....

 

Andrea, what about overlaying the UV as luminosity in the blue channel only?

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Seems like there should be some way to just compress the wider visual frequency range into our visible range. All our natural colors would be proportionally red shifted with UV shifted into visible.

 

Yes, you can do this in a simple RGB channel stack. Channel stacks are used regularly by many and have been shown in various places on UVP. (And software has been written to automate this.)

 

You would load the UV photo into a new Blue channel to "shift" UV "upwards" or "to the right" (however you are looking at it).

Then load the Blue channel from the Visible photo into a new Green channel.

And finally load the Green channel from the Visible photo into a new Red channel.

 

So your new RGB stack consists of the following using my shorthand way of describing it.

R = Gvis

G = Bvis

B = UV (or Buv)

 

The thing which gets lost here is the original visible Red data.

When you map 4 dimensions onto 3 dimenions, something will always get "lost", in a sense.

 

I usually attempt to make a channel stack where the UV is placed into

a new Red channel because UV typically has the most information in its Red channel.

I take the original Green and Blue channels from the Visible photo and put them into new G and B channels respectively.

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I know what you are talking about, shifting UV into B, B to G & G to R. I meant without losing the red data. Another way to describe what I am asking is, how might we remap the Vis colors to warmer false colors enough to leave space for the UV to map into the blue end?

 

Added

I have used LUTs to make pseudocolor images from monochromatic radiographs. This is essentially how a pseudocolor display from a thermal imager is formed.

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By "warming" the visible colours you will be losing their blue data.

 

You could try (and I have done this) a Purple, GreenBlue, Orange stack.

 

Purple = (128,0,255)

GreenBlue = (0,255,128)

Orange = (255,128,0)

 

Put the UV into the Purple channel.

Put the Visible into the BlueGreen and Orange (GreenRed) channels.

 

Edit: I got those RGB values wrong the first time through.

 

 

Or a Yellow, Magenta, Cyan stack.

Put UV into Magenta.

And Visible into Yellow (red-green) and Cyan (green-blue).

Some red and blue are lost in the Visible, but some is preserved.

 

However, when you put these things together they don't really tell you much.

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