Tuesday, August 31, 2010

Protosphyraena perniciosa in Stereo

It’s a kind of magic.

One shaft of light
That shows the way.

~ lyrics from Kind of Magic, a song written by
 Roger Taylor and performed by Queen

Gentle Warning:  If you thought that the Magic Eye books of the mid-1990s were the work of the devil, you may have a problem with this posting.

During the Late Cretaceous, the Western Interior Sea occupied a broad swath of the interior of North America, stretching the entire length of the continent.  The map below, created by Ron Blakey, professor emeritus of geology at Northern Arizona University, shows North America and its inland sea about 75 million years ago.  (A rich array of paleogeographic maps is available on Blakey’s website.)

Many fossils from the predators and prey that lived in this marine environment are preserved in the Smoky Hill Chalk of northwestern Kansas, a chalky limestone deposited about 82 to 87 million years ago.  The local landscape in that part of Kansas is startling (to this Easterner), to say the least, offering a western John Ford-like landscape.  Mike Everhart’s Oceans of Kansas website offers a collection of pictures of the Smoky Hill Chalk which capture their badlands flavor.

Among the fierce predators of these waters was Protosphyraena perniciosa, a fish with a mouthful of forward-thrusting dagger-like teeth, a long pointed beak, and dangerous front fins.  Think swordfish starring in a nightmare.  Everhart’s informative overview of the Protosphyraena perniciosa on his website includes a painting recreating this disturbing monster.  The 3 cm. long tooth from a Protosphyraena perniciosa pictured below was collected (not by me) from the Smoky Hill Chalk in Gove County, Kansas.

The technique I’m using here to depict this tooth is appropriate, I think, for this especially horrific fish.  The two images in this picture are of the same tooth but, despite appearances to the contrary, are not identical.  Previously on this blog, I’ve pondered how to capture images of fossils.  Being open to the unbidden means that inspiration can come from anywhere.  So it was that earlier this summer I happened to catch Terry Gross’ interview with Brian May on her NPR show Fresh Air (August 3, 2010).  May was lead guitarist and a composer (e.g., We Will Rock You) with the storied rock group Queen.  But, lest one think he’s a burned out rocker drifting through life living on his royalties, know also that he is an astrophysicist, having earned his Ph.D. in astrophysics from Imperial College, London, in 2007.  Terry Gross’ primary interest in this interview was in May’s role in Queen and how songs were composed and played by the group.  A worthy topic since May brought intellect and science to it.  Almost tangential in this interview (but what I suspect he really wanted to spend much more time discussing) was one of his consuming interests (besides astrophysics) – stereoscopic photographs or stereoviews – which is the subject of a book he recently co-authored with Elena Vidal, entitled A Village Lost and Found:  A complete annotated collection of the original 1850s stereoscopic photograph series – Scenes in Our Village by T.R. William (2009).  This is an amazing work, as fascinating for its exploration of the quiet, small village of Hinton Waldrist in mid-19th Century England, as for its glimpses of the broader world of stereoviews.  What little I know about stereoviews (and share below) I learned from this wonderful book.  It comes with a stereoscope (see picture below).

Stereoviews came into being in the early days of photography at the beginning of the 19th Century.  It was dissatisfying to some that photographs captured only two dimensions, offering a flat representation of reality, so they looked for ways to bring depth, the third dimension, into the images.  They built on the techniques already being used for “stereo” drawings and created stereoscopic pictures which, when properly viewed, offered a view with depth, a view in stereo.

To do this, they took advantage of the fact that we humans have two eyes set a bit apart from each other, giving us binocular vision.  As a consequence, stereoviews hold two pictures of the same scene; these right and left images are shot from slightly different positions, the camera having moved horizontally between each exposure (unless it’s a camera designed specifically to take these dual pictures).  Viewed through a stereoscope or by free-viewing (more on that in a moment), these dual photographs are processed by the brain as a three-dimensional image.

[This ability of the brain] is no accident.  Through the long, leisurely process of our evolution as a species, having two slightly different views of the same scene gave humans (any many other species) a great advantage . . . . [T]his binocular vision gave us the ability to perceive depth, enabling us to instantly recognise how far away each object in our sight was, a vital factor in assessing how close to us a potential danger might be.
                            A Village Lost and Found, p.12

The two images above of the Protosphyraena perniciosa tooth are sequential stereo photographs which, if viewed through a stereoscope (such as the one shown below), depicts the tooth in three dimensions.

But, that’s not the only way to see the stereoscopic image.  There’s free-viewing, a technique that many of us used in the mid 1990s when the various Magic Eye books were populating the New York Times best seller lists.  (As with nearly everything else in life, Magic Eye also made an appearance on Seinfeld.)  Free-viewing works not only on printed images but on images displayed on a computer screen.

May and Vidal offer this guidance for free-viewing stereoscopic pictures:

All we need to do is line our head up squarely with the page, and imagine we are looking through the page to infinity.  Usually what happens is that the two images in front of us both become double, and four images swim about sideways, as we try to make sense of what we are seeing.  If we persevere, though, and keep the eyes relaxed, eventually we will see two of the four images coalesce into one.  This become the central, solid picture, and is flanked by two other pictures, which both appear partly transparent.  All we need to do now is forget about the outside pictures, and concentrate gently on the centre one.  With a little patience, it is possible to keep the convergence of our eyes constant, so the central picture keeps its integrity, but relax the focus of the eyes to make this picture sharp.  At this point, the magic happens, we are suddenly aware that the central picture is no longer flat, but completely three-dimensional . . . the window is open . . . we are free-viewing in stereo.
                        A Village Lost and Found, p. 15

Well, I suspect the process is a bit different with everyone, and, I know, impossible for some.  With the images of the tooth above, the process for me seems to be a bit simpler, perhaps because there’s less information in the photographs for my brain to deal with than there is with the stereoviews of the village of Hinton Waldrist.

Here’s how it works with me on the tooth images.  As I bring my face close, centering my nose between the two pictures, I try to look beyond the pictures.  Up close to the pictures, I see a central, blurry image.  Then, as I slowly move back from the pictures, I keep focused on the convergence image.  Two other images appear on the left and right.  I ignore them and stay focused on the central image.  Not too far removed from the page, the central image comes into focus in three dimensions.

May and Vidal have other good advice – it may not happen the first time or the second . . . .  

As I noted, these techniques work on images on a computer screen.  But, if the dual image of the tooth is printed for stereographic viewing, I find that it works wells for me if the composite picture is about 3 3/8th inches high and some 4 ¼ inches wide.  Clearly a range of sizes will work, so there’s not anything particularly magical about these dimensions.

And to be honest, in many stereoviews, objects all at the same range often seem to have retained a two-dimensional quality.

Each of the images in the Scenes in Our Village series was accompanied by a verse, presumably written by the photographer T. R. Williams.  May and Vidal liken their spirit to that of haikus.  I loved the one in which the poet extols the virtue of stereoscopic viewing as a way of giving the untrained eye a glimpse of deeper beauty.

Lane Leading To The Farm

Seen with the artist’s eye, how many a spot
On nature’s face that seems a simple blot,
Teems with rich images and beauties rare!
Taught to appreciate, the traveller there
Marvels that he so often hath before
Unknowing, unadmiring, passed it o’er:
Thus, what is cultivation to the eye
Of the taught artist – stereoscopes supply.

[Note: I later edited this post by adding in various places the term "stereoview" which is the more common label applied to this two-picture arrangement.]

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