118 lines
5.5 KiB
Markdown
118 lines
5.5 KiB
Markdown
---
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title: "Pi pan-tilt for huge images, part 1: introduction"
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author: Chris Hodapp
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date: "2016-09-25"
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tags:
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- photography
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- electronics
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- raspberrypi
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---
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Earlier this year I was turning around ideas in my head - perhaps
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inspired by Dr. Essa's excellent class,
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[CS6475: Computational Photography][cs6475] - about the possibility of
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making an inexpensive, relatively turn-key rig for creating very
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high-detail photographs, ideally in HDR, and taking advantage of
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algorithms, automation, and redundancy to work with cheap optics and
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cheap sensors. What I had in mind had a pretty commonly-seen starting
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point for making panoramas - something like a telephoto lens mounted
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on a pan-tilt gimbal, and software behind it responsible for shooting
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the right pattern of photographs, handling correct exposures,
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capturing all the data, and stitching it.
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My aim wasn't so much to produce panoramas as it was to produce very
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high-detail images, of which panoramas are one type. I'd like it to
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be possible for narrow angles of view too.
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Most of my thoughts landed at the same inevitable view that this would
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require lots of custom hardware and electronics, and perhaps from
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there still may need a mobile app to handle all of the heavy
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computations.
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Interestingly, this whole time I had several Raspberry Pis, an
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[ArduCam][] board, work history that familiarized me with some of the
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cheaper M12 & CS mount lenses of the telephoto variety, and access to
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a [hackerspace][hive13] with laser cutters and CNCs. Eventually, I
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realized the rather obvious idea that the Pi and ArduCam would
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probably do exactly what I needed.
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A few other designs (like [this][makezine] and [this][scraptopower])
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offered some inspiration, and after iterating on a design a few times
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I eventually had something mostly out of laser-cut plywood, hardware
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store parts, and [cheap steppers][steppers]. It looks something like
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this, mounted on a small tripod:
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I am able to move the steppers thanks to [Matt's code][raspi-spy] and
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capture images with [raspistill][]. The arrangement here provides two
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axes, pitch and yaw (or, pan and tilt). I put together some code to
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move the steppers in a 2D grid pattern of a certain size and number of
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points. (Side note: raspistill can
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[capture 10-bit raw Bayer data][forum-raw-images] with the `--raw`
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option, which is very nice. I'm not doing this yet, however.)
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Here's a video of it moving in such a pattern (to speed things along,
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image capture was replaced by a 1/2 second delay at each point):
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<iframe width="560" height="315"
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src="https://www.youtube.com/embed/jO3SBandiUs" frameborder="0"
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allowfullscreen></iframe>
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It's still rather rough to use, but it worked well enough that I
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picked up a [25mm M12 lens][25mm-lens] - still an angle of view of
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about 10 degrees on this sensor - and set it up in the park for a test
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run:
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(*Later note*: I didn't actually use the 25mm lens on that shot. I
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used a 4mm (or something) lens that looks pretty much the same, and
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didn't realize it until later. It's a wonder that Hugin was able to
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stitch the shots at all.)
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The laptop is mainly there so that I can SSH into the Pi to control
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things and to use [RPi-Cam-Web-Interface][] to focus the lens. The
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red cord is just Cat 6 connecting their NICs together; the Pi is
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running off of battery here. If I had a wireless adapter on hand (or
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just a Raspberry Pi 3) I could probably have just set up a WiFi
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hotspot from the Pi and done all this from a phone.
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I collected 40 or 50 images as the stepper moved through the grid.
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While I fixed the exposure and ISO values with raspistill, I didn't
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attempt any bracketing for HDR, and I left whitebalance at whatever
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the camera module felt like doing, which almost certainly varied from
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picture to picture. Automatic whitebalance won't matter when I start
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using the raw Bayer data, but for the first attempt at stitching, I
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used only the JPEGs which already had whitebalance applied.
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I stitched everything in Hugin on my desktop PC. I would like to
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eventually make stitching possible just on the Raspberry Pi, which
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isn't *that* farfetched considering that I stitched my first panoramas
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on a box that wasn't much more powerful than a Pi. I also had to get
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rid of some of the images because for whatever reason Hugin's
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optimization was failing when they were present. However, being able
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to look at Hugin's computed pitch, yaw, and roll values and see
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everything lining up nicely with the motion of the steppers is a good
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sign.
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The first results look decent, but fuzzy, as $10 optics are prone to
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produce:
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[{width=100%}](http://i.imgur.com/zwIJpFn.jpg)
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Follow along to [part 2](./2016-10-04-pi-pan-tilt-2.html).
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[cs6475]: https://www.omscs.gatech.edu/cs-6475-computational-photography
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[ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
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[hive13]: http://hive13.org/
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[makezine]: http://makezine.com/projects/high-resolution-panorama-photography-rig/
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[scraptopower]: http://www.scraptopower.co.uk/Raspberry-Pi/raspberry-pi-diy-pan-tilt-plans
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[steppers]: https://www.amazon.com/Elegoo-28BYJ-48-ULN2003-Stepper-Arduino/dp/B01CP18J4A
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[raspi-spy]: http://www.raspberrypi-spy.co.uk/2012/07/stepper-motor-control-in-python/
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[forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138
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[raspistill]: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md
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[RPi-Cam-Web-Interface]: http://elinux.org/RPi-Cam-Web-Interface
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[25mm-lens]: https://www.amazon.com/gp/product/B00N3ZPTE6
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[Hugin]: http://wiki.panotools.org/Hugin
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