Megapixels, Shmegapixels: How to Make Great GIGAPIXEL Images With Your Humble Digital Camera

6/6/08Follow @wroush

Size matters, at least when it comes to the resolution of digital photos. As much as I love my iPhone, its built-in 1200×1600-pixel camera just doesn’t work for serious photography. Problem is, it’s been my only camera for almost a year, ever since my previous digicam croaked during a cross-country road trip. But a couple of weeks ago I found a very reasonable price ($314) on a Canon Powershot S5, which has maximum resolution of 3264×2448 pixels, or 8 megapixels. That’s enough to make nice 16-by-20-inch prints, and should be plenty, practically speaking, for anyone but a professional photographer.

Or so I thought. But I’ve recently become intrigued with a form of digital photography that takes image size to a new extreme: super-high-resolution or “gigapixel” imaging. Gigapixel photography isn’t about making bigger prints—it’s about gawking at the images themselves on the screen, sort of the way you’d watch hummingbirds fly in super-slow-motion in a Discovery Channel show on your HDTV. Such images contain such an overwhelming amount of detail that you’re not really supposed to download or view them all at once—rather, you use a combination of Web streaming technology and scrolling and zooming tools to dive deeper and deeper, in much the same way that software like Google Earth allows you to zoom from a view of the entire planet to a view of your backyard.

Of course, there’s no commercially available camera that can actually take pictures with billions of pixels. Hasselblad’s H2D-39, a $31,000 device based on Kodak’s 39-megapixel CCD, represents the rough upper limit today. To make images bigger than that, you have to stitch multiple photos together using graphics software. And lately, two things have happened to make gigapixel photography a practical pastime for amateur photographers: professional-grade stitching software has become more affordable, and there’s at least one online community, GigaPan.org, where you can upload and share your gigapixel images.

I mentioned the GigaPan site briefly in my first World Wide Wade column back in April. It’s not a Flickr-style commercial photo-sharing site, but rather an outgrowth of a collaborative research project between Google, Carnegie Mellon University, the Intelligent Robotics Group at NASA Ames Research Center, and an Austin, TX, hardware maker called Charmed Labs. This fall Charmed is bringing out the Gigapan Robotic Imager, a motorized platform for consumer digital cameras. The device precisely controls a camera’s pan and tilt, guiding it through dozens or hundreds of overlapping snapshots that can be stitched together later to create huge panoramas or mosaics. (NASA probes such as the Mars Phoenix lander generate panoramas of the Martian landscape in much the same way.)

But you don’t need a fancy device like the Gigapan robot to make great panoramic photos. And while GigaPan.org was originally developed as a showcase for images created using the Charmed Labs imager, anyone is free to upload their panoramas to the site. There’s just one catch: unlike other photo-sharing sites such as Flickr, which has an upper limit of 20 megabytes on the size of the photos you can upload, GigaPan has a lower limit: images must be at least 50 megabytes in size!

As a weekend project, I decided to see what kinds of panoramas and mosaics I could make for the GigaPan site using my new Canon. I grabbed my tripod and trooped over to Boston’s Copley Square, home to architectural gems such as Trinity Church, the John Hancock Tower, the Boston Public Library, and Old South Church.

Copley Square Panorama, Assembled Using PhotoStitch (Click for Larger Version)Like most Powershot models, the S5 has a built-in “stitch assist” mode that helps you take a series of images from left to right. In other words, it shows the rightmost edge of your previous photograph on the screen to help you line up the next shot, theoretically leaving enough overlap so that photo-stitching software can later create a seamless panorama. Notice I said “theoretically.” I used stitch assist mode to take 13 successive images of Copley Square, but when I got home and used the Canon PhotoStitch software that came with my camera to assemble the images, the resulting image (click on the link or on the thumbnail above to see it) was less than ideal. Not only did the software have a tough time lining up the images correctly, but the final panorama suffered from optical distortions that made most of the buildings in the photo lean precariously, as if gravity had gone askew.

It wasn’t really the software’s fault—it just wasn’t made to deal with a particular challenge in photography called the “keystone effect.” If you’re standing on a sidewalk and looking up at a building, perspective will naturally cause the higher floors of the building to look narrower. Our brains seem to correct for this effect most of the time, so we don’t really notice it. But photographs have a way of calling attention to it, and one result is that a tall building (or any vertical edge) that isn’t near the center of an image will appear to lean perilously toward the center line. Since a panorama consists of a series of individual photographs—each one keystoned around its own center line—the collection as a whole can be vertigo-inducing, with buildings tilting every which way. To fix the problem, you need better software.

Copley Square Panorama, Assembled Using Canon PTGuiSo I downloaded the trial version of a program called PTGui (for Panorama Tools Graphical User Interface), one of the third-party products recommended by GigaPan.org. (The Gigapan device will come with its own stitcher software.) Made by a small software company in the Netherlands called New House Internet Services, PTGui includes a mess of clever features that correct problems like keystoning. I don’t really know how it works, but I’m guessing that the software has edge-detection algorithms that help it select the portions of each image that are least affected by keystoning; it may also rotate individual photos as necessary to make vertical lines look vertical. To see how well it works, just take a gander at the alternate panorama I made with PTGui, using the same source images as before. In this image, the buildings are as straight as pine trees.

I also wanted to try making a large mosaic. So I positioned myself on a Copley Square sidewalk kitty-corner from Old South Church and … Next Page »

Wade Roush is a contributing editor at Xconomy. Follow @wroush

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