Would a sapient being sensitive to polarized light be able to see the angle of polarization in a photograph?

Question

Many animals have the ability to see polarized light (or rather, are sensitive to the direction of polarization), most notably birds and bees but also a wide range of other animals including cephalopods, many arthropods, and some vertebrates. Several of these species are thought to navigate by using the polarization patterns to determine the exact location of the sun, and use that as a compass to navigate. Some species are even capable of detecting polarized light in night conditions, thought exactly how is still controversial. Depictions of how these animals see polarized light (as well as mock-up devices intended to mimic this effect for human eyes) show the direction of polarization as banded patterns visible on the sky. Humans can see polarized light but we aren't that sensitive to it and can't use it to navigate like other animals can.

My question is this, given that these polarization patterns appear to be visible on the sky, would a sapient animal (that can therefore communicate what it sees) with the ability to see polarized light be able to identify the general orientation that a photograph or video had been taken from based on polarization patterns in the sky in the background? Or do most cameras not record that kind of information since the information being captured is intended for the human eye, which is more or less insensitive to polarized light?

EDIT: As a clarification, what I mean is would an alien sensitive towards polarized light be able to determine the direction at which a photograph or video was taken based on a photograph taken on a camera built by and for humans (i.e., cameras seen in everyday life), rather than a special camera built by the aliens specifically to take pictures/video accurate to their polarization-sensitive vision

Answer 1

You can test this for yourself by looking at a normal photograph through a polarising filter and rotating the filter. Unfortunately, I'm certain you'll find this has no effect, neither on a digital photograph nor a film one. (Well, for some digital displays you might find the whole image fades in and out, or you see colour fringes from a coating on the screen, but these effects don't correspond to the polarisation of the original scene.) Existing cameras aren't designed to record polarisation, and our displays and printing processes aren't capable of reproducing it.

I would guess that recording and reproducing light polarisation is at least as hard as recording and reproducing colour - which is to say, it could be done, but it wouldn't happen automatically, and it would take some effort to develop and implement the technology.

A human camera could easily be modified to record polarisation in a crude way, for example by taking a few shots in quick succession while rotating a polarising filter in front of the lens. (As John Dvorak points out in the comments, a total of three shots will do the job.) In principle it should be possible to develop a polarisation-sensitive CCD or CMOS sensor, but it would take some R&D, unless such a thing already exists for use in scientific instruments. A display that accurately reproduces polarised light would also require some effort to develop, although a crude approximation might be possible by just combining several projectors, each with a polarising filter, as is done for 3D movies. As Matthew points out in the comments, three projectors should be enough, or possibly only two, depending on how the aliens' eyes actually detect polarised light.

In short, as A. I. Breveleri's answer suggests, if the camera is designed by your aliens, it likely will record polarisation, just as our cameras record colours, but ordinary photos and movies don't include that information.

Answer 2

Humans and other people who cannot see polarization make and use cameras that do not record polarization. When cephalopods and other people who naturally see polarization use human cameras, they cannot see polarization in the photographs because human cameras do not record it.

Cephalopods have a word, "isogris", analogous to the human's "monochrome", to describe such limited photos.

Cephalopods are inspired to invent and produce cameras that capture and reproduce the polarization present when the photos are taken. Their finished developed photos emit polarized light. These photos look more natural to cephalopods, in the same way that color photos look more natural to humans.

Humans using such cameras are not aware of the polarization emitted by the resultant photos.

Humans who want to record polarization invent and produce cameras that capture polarization and record it as color or brightness, the way human monochrome cameras record colors as shades of gray. This is accomplished by adding a polarizing filter over the lens.

Humans using such cameras see a representation of the polarization, usually as varying color saturation.

There is no serious market among cephalopods for the inferior isogris human cameras.

Answer 3

@stephen-dadonna wrote in a comment:

Not an answer so I'll just comment: Sometimes the sky looks a deeper shade of blue in photographs that were taken with a polarizing filter oriented in a particular way. Perhaps a creature might be able to deduce polarization through the depth of colors in the sky or in reflections from water or oil slicks, etc.

I think the situation might be exactly analogous to the situation we have in real life with binocular vision and stereoscopic photographs (a.k.a. stereograms).

Humans evolved in a world where "judging the distance to a thing" was super important for survival. So we evolved binocular vision, which permits us to judge distance very well in the real world. But our camera technology is traditionally monocular — a photograph simulates the world as seen by a one-eyed person.

Perhaps your polarization-sensitive creatures evolved in a world where "judging the degree of polarization of light emitted from a thing" was super important for survival. How could this be so? (I have no suggestions.)

Can a human look at a flat photograph and "deduce" the Z-level of an object in it based on visual cues such as blurring, relative size, etc.? Sure. Of course, we're not 100% perfect at it. In fact there's a whole category of trick photography based on playing with this deduction — "Look, Aunt Betsy is on the same Z-level as the Tower of Pisa, and she's gigantic!" Perhaps your polarization-sensitive creatures would have similar "visual puns" based on perceived polarization, somehow.

What survival value is there in being able to deduce Z-level from a monocular image, given that humans already possess binocular vision? Well, the skill becomes useful if you accidentally lose an eye — not terribly uncommon in the state of nature, I'd think.

Similarly, humans are not-perfect-but-not-terrible at deducing color from a monochrome image; this skill is useful in twilight, when our visual apparatus becomes less sensitive to color but can still differentiate degrees of brightness pretty well.

(However, for a counterexample, humans are terrible at deducing color from a monochrome image taken under light of a pure wavelength, e.g. sodium light. That's not a skill with much evolutionary heft behind it.)

So, perhaps your polarization-sensitive creatures would develop "backup deductive abilities" to deduce polarization from color, if-and-only-if it was not uncommon for an individual to lose their polarization sense (say, through physical damage, or perhaps through illness or malnutrition).

Answer 4

Maybe... but probably not.

It's possible that an animal that is "used" to seeing polarization would be able to infer this information from a reproduction that lacks it, based on other effects. This would probably depend highly on what was photographed. A human could conceivably be trained to recognize the same sorts of cues.

However, as others have noted, human-designed cameras aren't designed to capture polarization information, nor are human-designed reproduction technologies generally concerned with reproducing polarization.

Moreover, accurate reproduction of polarized light such as you are describing would be quite difficult. You might, with sufficiently advanced deposition techniques, be able to lay down pigments in a way that produces the desired polarization, however this a) may be sensitive to the illuminating light source, and b) will probably more closely resemble the sort of lithography process used to produce complex microchips (e.g. CPUs) than inkjet printing (offset printing is right out). As a result, they will either be very expensive, or your hypothetical sophonts will be very good at nanomanufacturing, which will have a significant impact on many areas of their technology.

For emmisive displays, the situation is both better and worse. LCD technology leverages polarization in order to change the brightness of pixels. This means that pixel brightness and polarization direction, at least in a human-designed display, are directly coupled. The good news, however, is that I think you could replace the fixed polarization layer of a typical LCD with a second liquid crystal layer, which (in theory) would allow you to control the direction of polarization independent of the brightness. The same should be applicable to OLED displays, but note that you're going to be giving up a fair bit of brightness.

As to making a device that can capture polarization... I'm not aware of any sensor that can record it directly. The two techniques that come to mind are to have a polarization equivalent of a Bayer filter, which will of course eat in to your effective resolution, or read the sensor multiple times with a different, uniform polarization filter in place. (A bespoke camera might incorporate a liquid crystal layer in front of the sensor for this purpose.)

How do critters that can see polarization do it? Does biology have a solution, or does it "brute force" the problem as in one of my ideas? (AFAIK, biology detects color the same way as modern cameras, by having individual elements with different frequency responses; in effect, the Bayer filter is just copying from biology.)

Answer 5

This is not an answer, merely too much text for a comment. Sometimes this site sends me on fun research rabbit holes.

A 2018 article talked about birefringent printing, that is, intentionally printing something with variable polarization. Have a look at https://pubs.acs.org/doi/10.1021/acsami.8b14899

This leads me to think that all traditional printed photos would look flat to your aliens, with the reflected light partially polarized to the angle of the paper. You can buy polarization filters for screens, but that applies to the whole screen. It would all have the same flat look to your aliens.

As for imaging something with polarization, one way is to take a picture with a filter, rotate the filter, and take another picture. This isn't ideal, because some time has passed, and some parallax may be introduced by minor shifting of the camera. What about putting two cameras side-by-side, different rotations, and imaging at the same time? This has a worse parallax problem.

One group's solution in 2010 was to make a custom CCD with a checkerboard of filters, read each checkerboard square out. This would have to have very small checkerboard squares to look acceptable. With a similar output device, your aliens might be able to make a more lifelike screen. https://www.researchgate.net/publication/47404085_CCD_polarization_imaging_sensor_with_aluminum_nanowire_optical_filters

Answer 6

Polarization is a parameter of light, either when treated as a wave (with angle of polarization) or as photons (with polarization numbers). The reason you can't get polarization info from a photograph is that all this information is lost when the light is converted into electrons (in the case of solid-state sensors) or used to change molecular states (in the case of chemical film systems). All these cameras only report energy vs. position.

It would be possible in theory to do something like replacing the RGBG filters on top of camera sensor pixels with a set of filters with different polarizations, such as vertical, horizontal, and circular. Then some careful processing could generate multiple images which, by their difference in intensity patterns, indicate the distribution of different polarizations in the input.

For the purposes of SciFi, no reason an alien species couldn't have polarization-sensitive analogies to our color-cones in their retina.

Answer 7

No-ish

Edit: Rule #1: never pound out an answer in a short period of time.

It's important to understand that how we think of light mathematically is quite a bit different from what light actually is in reality. "They're either like infinitely small bullets flying in straight lines, or they're like enormous expanding [3-dimensional] EM pond-ripples from a thrown pebble." (William Beaty, 2004.)

Polarization is the perception of those "pond-ripples" on a single plane. When you look through a pair of polarized sunglasses (glasses that permit those "pond-ripples" through a narrow region of the 3-D pond (ideally a single 2-D plane, but I doubt the tech's anywhere near that good)¹ you're only seeing the photons that happen to conform to the polarizing matrix of the lenses. You're seeing some ripples, but not most or even all.

If you had a pair of glasses that were polarized to the same direction as your eyes, looking forward, but wrapped all the way around your head, you'd see the dark bands shown in your article about the bees. I'm unfamiliar with glasses designed this way, though, which is why no pair of polarized glasses I've used have produced the bands (I suspect they're designed such that the polarization reference is transverse to the plane of the lens and has nothing to do with which way your eyes are pointing).

The important point here is that light, itself, is only "polarized" artificially. In nature (as with our sunglasses), the bees eyes are designed to accept light along polarized lines, therefore accepting light along specific planes of the proverbial 3-D pond.

Why is this important? Because you appear to have not thought through the art of photography. People are rarely interested in taking an exact image of what they see (in fact, it's remarkably difficult to duplicate exactly what the eye sees). What they really want is something more idealized. In the professional/studio extreme this means that all shadows are controlled. The banding one of your articles refers to would be an undesirable distraction (like any other shadow we see today) that would be smoothed out with filters, diffractors, and all kinds of equipment.

At the other end of the spectrum are cheap cameras and amateur photographers — but even these want to minimize the undesirable effects to get that "ideal shot."

Finally, the photograph itself is reflecting light that's being perceived through polarized lenses. But the reflected light cannot reflect what the photograph depicts. If the camera has a polarized lens, it will show the kind of data you want to see — but the art of photography is to remove as much of that as possible.

Therefore, you need to make a choice. Do your characters want to see that polarized effect in their photographs or not? Do they, like we do ourselves, want all the distracting and extraneous shadows removed, to get the "perfect shot," or do they want something that's as close to what the eye sees as possible? (Which would be completely contrary to what we want to do today... please keep that very much in mind. It has nothing to do with whether or not we have polarized lenses.)

If they want the "perfect shot," your characters will be no more able to deduce things like the angle of light than we are today. (And we do analyze it. Forensics looks closely at imperfections like that to do exactly what you're thinking of.)

If they want "true to my eye" pictures, then they could deduce that kind of information.

Choose.

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_{¹ Or the exclusion of some of the infinitely small bullets, it depends on whether you want to think of them as particles or waves. In relation to this discussion, it doesn't really matter which you choose. I chose the pond metaphor.}