… but red-cyan anaglyphs are cooler
December 14, 2010
Over at his truly unique blog Paleo Errata, Jeff Martz is claiming that Stereopairs Are Cool. This assertion he supports with the following figure that he put together, showing a set of five stereopairs of a Longosuchus braincase:
Unfortunately, I am one of those who can’t “see” stereopairs, so these images are uninformative to me — or, at least, no more informative than your average inch-wide braincase photo.
So how else can we envisage the stereo information in these pairs of photos that Jeff took? My favourite way is using red-cyan anaglyphs — those goofy 3d images that you look at through 3d glasses. To compare, I did this to Jeff’s image. The process is simple: take two copies of the stereopair image, cut out all the right-eye views from one set and all the left-eye views from the other, then edit the colour levels of both layers. In one, take the red right down to zero, so you only have blue+green=cyan; in the other take the green and blue down so you only have red. Then stack one layer on top of the other and change its mode to “Lighten only”. Export the result as a JPEG and you get this result:
Armed with my red-cyan glasses (which, remember, I got as a freebie with a Lego catalogue), I can now make out the 3d structure really easily. Positives for the anaglyph approach:
- The 3D image is much easier to see
- The result takes up less space on the page
- Most importantly, the size limitation is removed: I have some beautiful whole-screen anaglyphs (e.g. Archbishop cervical, wallaby skull), whereas stereograms are restricted to a couple of inches’ separation.
The downside is, of course, that you need special equipment to see them –albeit equipment so laughably minimal that Amazon.com will sell you THREE PAIRS for $1.39, you cheap gits. But for those of who who are too poor to find $1.39, and who don’t have two friends with whom you can form an ad-hoc 3D-glasses buying consortium at a cost of $0.47 each, there is one further approach: a low-rent technique that I call a “wigglegram” for want of a better term. Here it is:
I discovered this approach by accident, when flipping through a bunch of photographs that I’d taken of, I think, the Archbishop. As a matter of policy, I take most of my photos twice, so that if I shake slightly or the auto exposure gets it wrong, I have a good copy that I can retain. I was trying to decide which of two nearly identical pictures to keep. But as it happened, I’d moved the camera slightly to the side between taking the first and the second, so as I skipped back and forth between them, I was seeing two slightly different perspectives.
So there you have it: three different ways to visualise 3d structure, each built from the same basic set of photos. They each have their merits, and I hope we’ll increasingly see more of all three of them, as we move into the Shiny Digital Future, and arbitrary limits on manuscript length and numbers of figures get lifted.
I leave y0u with an actual application of all this. Matt and I have, for some time, been working on a manuscript about caudal pneumaticity in sauropods, and we wanted to include a brief survey of which genera it’s been reported in. Among the candidates was Saltasaurus, which has a candidate pneumatic caudal vertebra that was illustrated thus by Powell (2003: plate 53, part 3):
Matt can “see” stereograms, and insisted that the dark patch on the side of the centrum is a pneumatic fossa. I wasn’t so sure, and in fact we got into quite an argument over whether or not to include this specimen in our list. The argument was neatly concluded when I had the obvious idea of converting Powell’s stereogram into an anaglyph:
As soon as I saw this, I recognised what the structure is: the crescent moon-shaped dark patch is indeed a deep, invasive fossa, and the broad, roughly circular object above it and to the right is a lumpen lateral process sticking right out into the camera (and partially hiding the fossa). So Matt was right, the vertebra is pneumatic, and a beautiful friendship was saved by the power of red-cyan anaglyphys. Yay!
- Powell, Jaime E. 2003. Revision of South American Titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects. Records of the Queen Victoria Museum 111: 1-94.