Agave Movie

When I moved from England to Tucson, Arizona in 1980, one of the things that fascinated me most was the desert vegetation. Among the most amazing plants were the agaves, which after a decade or more of slow growth decide one year to expend all their energies in the production of an enormous flower spike. Like Pacific salmon, they die after that one heroic shot at reproduction. The growth rate of the flower stalk- maybe twenty feet in a couple of months- is particularly remarkable when compared to the saguaro cacti that take decades to reach that height.

After watching this phenomenon for a couple of springtimes, I thought it would be interesting to make a time-lapse movie of it. I was therefore very pleased in April 1983 when I found not one, but two, side-by-side agaves beginning to bloom in a convenient location just behind Old Main on the University of Arizona campus, five minutes from my office.

I sunk a six-inch nail in the earth at what I thought was a suitable distance from the agaves, so I could take pictures from the exact same location once a week through the spring. I also tried to take the images at the same time of day each week, right after lunch at about 12:45pm. Unfortunately the prodigious growth of the agaves exceeded my expectations, and after about five weeks their tops started to disappear off the top of the camera field of view. I was forced to take two images to include the whole of each plant. Another problem occurred when I left for a couple of weeks in June to attend my sister's wedding in England. Gordy Bjoraker kindly agreed to fill in for me, and took the images while I was away.

After the project was complete and the U. of A. groundskeepers had removed the dying agaves, I printed out all the images, was fairly pleased with the results, and put the pictures away. Sixteen years later, with powerful image processing tools and a slide scanner at my disposal, I thought it would be worth re-reducing the data with the new technology. I scanned in all the images, mosaiced the pairs of frames taken when the agaves got too big for me, and made at least a first-order attempt to match the color balance and geometry of all the frames (not easy, as three different cameras were used in a range of lighting conditions with different films, and with only the six-inch nail as a guide the viewpoint and aim of the camera was never perfectly steady). Still, I'm quite pleased with the results.

Notes on image processing: mosaicing, color balancing and cosmetic fixes (such as adding blank sky to the tops of the early single-frame images) were done in Corel Photo-Paint 7.0. To register the images spatially I wrote an IDL routine that allowed me to specify a number of control points on each pair of images, and then did a Simplex search for the best combination of rotation, translation, and magnification to register the pair of images.

Things to notice in the movie, apart from the obvious flower spike:

And now, the movie...

Linked HTML pages

AVI file, reduced resolution (1 Mbyte size- currently garbled, on Unix systems at least)

The same scene over 18 years later, in November 2001 (slightly different viewpoint- the 6-inch nail was long gone). Much has changed, but the saguaro is still there, and the palo verde has grown to obscure much of it. The water spigot in the foreground has survived the decades, too.

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