Using the railway network as a flatbed scanner

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Using the railway network as a flatbed scanner

August 17th, 2026 — 4,600 words

Over the past few months, I've been working on using an industrial linear scanning camera to take very wide photos out of trains and ferries. Getting it working has been quite the challenge, but I think the results speak for themselves.

taken on the San Francisco to Oakland ferry in February 2026 (56,894x2,048 pixel grayscale image); scroll to zoom in and click and drag to move

More pictures are on display in the gallery.

I presented a talk on this project at EMFcamp 2026, which you can watch below or read on for the same story in more detail:

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What am I even looking at?

The process of capturing an image like the one of the container port above.

The camera is pointed out of a moving vehicle and is constantly capturing a single vertical line kinda like these grayscale ones in the diagram, but a lot thinner. As the camera moves, what exactly it sees is changing. If I capture the lines from the camera quickly enough and stitch them together, I can produce a complete-looking image. It's a bit more complicated than that and getting the results looking good was rather tricky, but that's the main idea behind it.

Background and Prior Art

Back in the 1990s, digital camera sensor technology hadn't caught up to the size and effective resolution of medium and large format film, so digital scanning backs were developed. They capture a high-resolution image without needing a giant grid of pixels by moving a single line of pixels (or three lines for color) across the frame. In the intervening years, image sensors have gotten pretty big (there's even one that covers 4x5" large format nowadays), but this approach is still cheaper to build for large formats than a giant sensor.

I'd been thinking about building my own digital scanning back for my large format camera for a while, but I've never quite gotten around to it because building something to mount properly on my camera seemed too daunting. (Buying one could have been an option, but ones from the 1990s still go for thousands of dollars on ebay and require reconstructing a computing environment of a similar vintage to use.) Late last year, I was watching a video on Gigawipf's medium format scanning camera build and suddenly thought: "what if the entire camera moved and the subject didn't?" and decided to give it a shot.

Loading film into my large format camera on top of a mountain in Vermont because I'm allergic to doing photography in a normal way. (The resulting pictures from that trip are here.)

I found some previous photos in the same vein (the Scannoramic project, John Hikerbiker's experiment, Daniel Lawrence Lu's reversal of his stationary camera, and Martin Liebscher's very interesting film shots), but the results seemed like they could be improved upon. Surely taking the speed of motion into account and getting cleaner results wouldn't be too hard, right?

Slit Scanning My Sofa

On the night I thought up this "big scanner" concept, I had to give it a shot. It was a bit late to go out and catch a train, so I scanned my sofa instead.

I set my phone on my office chair and slowly pushed it along as it captured a video. I then wrote some really slapdash code (which I am choosing not to share here to protect my readers) to grab the leftmost column (a "slit") of each frame and combine them into an image.

My comments included lyrics from "Future Me Hates Me" by The Beths, which became something of a self-fulfilling prophecy when I started writing a postprocessor for the next version of the camera loosely based on that code and cursed my decisions.

It looks vaguely like my sofa, but it's rather squished and the art on the wall is unintelligible. Surely I can do better.

I messed around with the postprocessing and doubled every column, which makes it look less squished, but it's still a mess because I wasn't pushing the chair at a particularly consistent speed.

I knew from the start that I'd need to measure the speed somehow, but I was naïvely hoping that I wouldn't need to measure it that well and could simply fudge it. This image, however, shows that even small variations of speed matter. This was my first glimpse into how much of a pain dealing with speed would turn out to be.

For my next trick, I took a ride on the MBTA orange line. I taped my old phone to the seat to use its accelerometer and held my current phone to the window, making sure to turn the frame rate up all the way to 60 fps.

The accelerometer data wasn't very useful and was even less so when I took an integral to get velocity.

If I remember correctly, y was the axis of the train's movement, but the data is so noisy that the train was apparently moving backwards at the end.

The result looks interesting, though, but I definitely need more lines if I want a properly intelligible image.

While I was getting ready for EMFcamp, I noticed...