into the infrared

It's a lazy Easter Sunday, with no plans other than to lounge around the loft with the Spousal Unit and resident cat, surfing the InterTubes for amusing items -- like this wonderful site detailing fiendish experiments on Peeps -- perhaps pausing now and then to reflect on Life With a Capital "L." Among other things, I was shocked to realize that I am more than halfway through my three-month fellowship at KITP, with only four more "Journal Club" sessions to go. It's been a lot of fun: we've had sessions on "The Art of the Book Deal"; a rousing panel discussion on ongoing tensions between scientists and the media (which the Spousal Unit describes at length here); a brainstorming session on scientists in Hollywood, in which we devised the framework for a physics-centric (or at least science-centric) TV series; and of course, a session on Science Blogging 101, in which I set up a blog for our cat, Clio, on Blogger just to illustrate how easy it is. (If Chad at Uncertain Principles can write a book about conversations with his dog about quantum mechanics, Clio can have her own blog.)

My musings reminded me that I've been meaning to write a post about the infrared photography of Caltech's Tom Prince, who's currently at KITP on sabbatical before heading back to Pasadena to take the helm of the newly funded Keck Institute for Space Studies. We hope it will be abbreviated KISS, making it possibly the best science acronym ever. As a handful of shyer souls beat a hasty exit when I asked if anyone wanted to participate in a practice press conference, Tom graciously volunteered to be the guinea pig during the session on Press Conference Protocol. (I have since learned to give people advance notice and ferret out volunteers beforehand.) He spoke for 10 minutes or so about his hobby -- complete with sample photographs of KITP in the infrared -- and took a few questions from the audience afterward. The photographs are truly stunning. Check this out:

And here's another that captures the nearby beach and big blue sky:

It's tough to pinpoint at first what makes these photographs so striking, but it's related to the properties of near-infrared light -- i.e., light just beyond the visible spectrum (wavelengths between 700 nm to 1200 nm, usually falling around 900 nm). Infrared photography records what the human eye cannot see. Many materials reflect and transmit IR light in a different manner than visible light. So there are elements in IR images that resemble photographic negatives (although these pix are clearly not negatives). Blues, browns and dark greens in shadow appear dark, while reds, whites and greens in sunlight appear light. Take a portrait of your loved one and the skin will have a chalky appearance in the IR image, red lips will be pale, and the eyes will show up as dark spots. Vegetation comes out very bright in IR photographs, while a clear sky appears dark, apart from the occasional white cloud.

Andrew Davidhazy of the Imaging and Photographic Technology Department at the Rochester Institute of Technology explains on his Website that this last effect occurs because of "the high near-infrared transmission characteristics of green chlorophyll and high infrared reflectance of the underlying cellulosic structure of these subjects." Among other things, this can be used in aerial surveys and reconnaissance to distinguish trees and grass from diseased or dead trees or burned grass, since those appear dark in IR photographs. (You do need to use a special filter for IR photography, and special IR film if you're using a traditional camera, since otherwise the infrared effect is masked by the exposure to visible light. And  note that this is not the same thing as thermal imaging: IR photography uses radiation reflected from the subject to form images, whereas thermography uses IR radiation naturally emitted by objects, and requires special IR sensors.)

Ideally, the photographer takes all these effects into consideration when composing a scene or choosing topics. Tom said that he tries to take his photographs on bright sunny days -- very common in Santa Barbara -- because there is more IR light when the sun is bright, making the high-contrast effects that much stronger, although he's gotten some interesting, moodier effects in photographs taken on cloudy days. Other suggestions from IR photographers include taking pictures in a graveyard, because the grass will come out almost completely white, with the dark tombstone seeming to almost float eerily in space. Stone buildings covered in ivy or other creeping vegetation also yield striking, high-contrast IR images. And apparently, if you photograph people wearing sunglasses, it's sometimes possible to see the eyes behind the opaque shades in an IR photograph, because the filters used in the sunglasses don't have any effect on IR light.

Tom is just one among thousands of IR photography enthusiasts around the world, as I discovered when I Googled the term after his talk. My research yielded a rich lode of fascinating details. I already knew that infrared light was discovered by Sir Frederick William Herschel, best known for building killer telescopes in the 18th century and discovering the planet Uranus. In 1800, Herschel took some time away from his telescopic observations to fiddle with a different kind of experiment: passing sunlight through different colored filters. The different colors seemed to pass different amounts of heat, so he took things one step further, and passed sunlight through a glass prism to create the telltale rainbow spectrum of visible light. Then he measured the temperature of each bulb.

Herschel found that not only were all the measured temperatures higher than the controls, but those temperatures increased with each color from the violet to the red part of the spectrum. And when he decided, just for curiosity's sake, to measure the temperature just beyond the red portion of the visible spectrum, it had the highest temperature of all. Herschel attributed the effect to "calorific rays," and subsequent experiments demonstrated that they behaved just like visible light -- not surprising, since what he'd discovered was infrared radiation. It was the first demonstration that there were types of light beyond the visible spectrum.

Infrared radiation spawned not only a host of practical applications, but also an entire field of astronomy. Infrared telescopes can see past the huge amounts of interstellar dust in the cosmos into the very hearts of galaxies. People had figured out how to take infrared photographs as recently as the 19th century, but it wasn't easy. In the early 20th century, however, scientists developed special infrared dye sensitizers to create infrared films, and the use quickly spread from the laboratory into more practical applications. In the late 1920s, for instance, John Logie Baird developed the first working infrared videosystem, Noctovision, which, among other things, made it possible to film nighttime scenes during the day (a technique known as "day for night," or, as Jen-Luc Piquant prefers to phrase it, La Nuit Americaine). Just underexpose the shot a little bit; then a dark sky with bright moon-lit clouds and deep shadows looks pretty much how we'd expect a nighttime scene to appear.

Today, IR photography has found application in the study of plant diseases, revealing changes in pigment or cellular material; in paleobotany; to enhance details of deeply pigmented tissues in photomicrography in the biological sciences; and by the textile industry to detect irregularities in fibers. It is also used quite often in criminal investigations to examine and identify cloth, fibers and hair, and it's become a standard laboratory tool for imaging faded, damaged or altered documents. It makes clear the differentiation between pigments, dyes and inks, so if something has been overwritten, you can sometimes figure out the underlying text using IR imaging techniques. This proved handy in the 1930s, for example, when people wanted to see what lay underneath the blacked-out portions of documents vetted through censors.

Davidhazy has a terrific example of this infrared luminescence (or fluorescence in the infrared) on his Website. Twenty years earlier, a mother had placed a letter to her children in a homemade time capsule and buried it near the cornerstone of their house, intending it to be unearthed and read 20 years into the future. Unfortunately, when he now-grown children did so, much of the ink had washed away because water had seeped into the box. There was residual ink, however, albeit not visible to the human eye. When the letter was illminated with light devoid of IR wavelengths, the residual inks fluoresced in the infrared, and when filtered through an IR transmitting filter placed over the lens of a camera, those emissions were captured on Kodak high-speed infrared film. And the children were able to read their mother's words after all.

The rise of the digital camera is beginning to eclipse the use of actual IR film and traditional cameras. No longer is there any need to fuss with all those chemical and mechanical processes. Instead of focusing reflected incoming light onto a piece of film, a digital camera focuses that light onto a semiconductor device -- either a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) technology -- that records light electronically, converting that light into electrical charges.

The CCD and CMOS chips used in digital cameras are already very sensitive to near infrared, not just visible light, which is why these cameras come equipped with filters to remove the infrared. Tom Prince simply adapted his standard digital camera with an opaque filter that cuts out the visible light and enhances the infrared, for a cost of roughly $250. (He doesn't recommend doing so yourself unless you have easy access to a clean room, as it requires opening the camera and exposing the delicate electronic innards to particles in the environment.) Using such a filter, you can't see the shot through the viewfinder. Tom (and, I assume, other IR photographers) have to compose the shot with the filter off, steady the camera in place, put the filter back on, adjust the focus, and then take the shot. It's a little hit and miss, but as the images featured in this post attest, you can get some genuine stunners.

So what happens when you take a color photograph using an infrared filter? Tom has tried that, too, and it is possible to do so. It's just a bit more work, since you need to take two pictures: one with the IR filter, and immediately after, another regular photograph. They need to be in alignment, too, so most IR hobbyists recommend using a sturdy tripod to hold the camera in place. And don't forget to take both photos with the same aperture settings to ensure consistent depth of field. The two photos can then be merged in Photoshop, where one can modify the color channels directly. Any color image can be broken down into the red, green, and blue channels (which is how color images are created); IR light in that context is just another "channel." Here's one of Tom's color IR photographs:

The overall effect isn't quite so much of an eerie contrast, although one still gets the sense of something being "different" about the photograph. Here's the same scene in standard IR black-and-white, for comparison:

You can see many other examples of infrared photography by several different photographers by browsing this gallery of links, and several examples comparing and contrasting color and B&W IR photographs here. Why not browse a little bit and savor a novel way of looking at the world? It's way cooler than rose-colored glasses.

Comments

[Traums]

Aren't different species capable of viewing different wavelength ranges?
Bees for example, have an in-built bias when it comes to choosing which flowers to suck nectar from (and hence pollinate): http://son.nasa.gov/tass/images/cont_emsp4.jpg

[Traums]

Also interesting is to note that blue light scatters more in the atmosphere than longer wavelengths. The sky appear very bright in UV, limited only by intensity.
http://www.naturfotograf.com/images/B000528165.jpg

[eingram]

I came across this comment and am rather belatedly metacommenting:
["We could make jokes about top and bottom here, but that would just be tasteless. Please resist the temptation yourselves and aspire to a higher brand of humor."

Yeah, quark jokes just aren't a good flavor of humor. We need to bring them up to a higher level of taste; I'm not down with this mindless juvenility. You might think such remarks are charming, but honestly they're just strange.]
(Posted by Chris, october 30, 2007)
Yes puns are at the bottom of the humor scale, but Chris is on top of the quarkuation.(quark situation), pun-ditly speaking.