92c4efac7d
I needed the ability to use ATTR_HTML in org-mode: https://github.com/jgm/pandoc/pull/2927 Doing this update required me to fix somes YAML in some posts.
115 lines
5.7 KiB
Markdown
115 lines
5.7 KiB
Markdown
---
|
|
title: "Pi pan-tilt for huge images, part 1: introduction"
|
|
author: Chris Hodapp
|
|
date: September 23, 2016
|
|
tags: photography, electronics, raspberrypi
|
|
---
|
|
|
|
Earlier this year I was turning around ideas in my head - perhaps
|
|
inspired by Dr. Essa's excellent class,
|
|
[CS6475: Computational Photography][cs6475] - about the possibility of
|
|
making an inexpensive, relatively turn-key rig for creating very
|
|
high-detail photographs, ideally in HDR, and taking advantage of
|
|
algorithms, automation, and redundancy to work with cheap optics and
|
|
cheap sensors. What I had in mind had a pretty commonly-seen starting
|
|
point for making panoramas - something like a telephoto lens mounted
|
|
on a pan-tilt gimbal, and software behind it responsible for shooting
|
|
the right pattern of photographs, handling correct exposures,
|
|
capturing all the data, and stitching it.
|
|
|
|
My aim wasn't so much to produce panoramas as it was to produce very
|
|
high-detail images, of which panoramas are one type. I'd like it to
|
|
be possible for narrow angles of view too.
|
|
|
|
Most of my thoughts landed at the same inevitable view that this would
|
|
require lots of custom hardware and electronics, and perhaps from
|
|
there still may need a mobile app to handle all of the heavy
|
|
computations.
|
|
|
|
Interestingly, this whole time I had several Raspberry Pis, an
|
|
[ArduCam][] board, work history that familiarized me with some of the
|
|
cheaper M12 & CS mount lenses of the telephoto variety, and access to
|
|
a [hackerspace][hive13] with laser cutters and CNCs. Eventually, I
|
|
realized the rather obvious idea that the Pi and ArduCam would
|
|
probably do exactly what I needed.
|
|
|
|
A few other designs (like [this][makezine] and [this][scraptopower])
|
|
offered some inspiration, and after iterating on a design a few times
|
|
I eventually had something mostly out of laser-cut plywood, hardware
|
|
store parts, and [cheap steppers][steppers]. It looks something like
|
|
this, mounted on a small tripod:
|
|
|
|
[{width=100%}](../images/2016-09-25-pi-pan-tilt-1/IMG_20160912_144539.jpg)
|
|
|
|
I am able to move the steppers thanks to [Matt's code][raspi-spy] and
|
|
capture images with [raspistill][]. The arrangement here provides two
|
|
axes, pitch and yaw (or, pan and tilt). I put together some code to
|
|
move the steppers in a 2D grid pattern of a certain size and number of
|
|
points. (Side note: raspistill can
|
|
[capture 10-bit raw Bayer data][forum-raw-images] with the `--raw`
|
|
option, which is very nice. I'm not doing this yet, however.)
|
|
|
|
Here's a video of it moving in such a pattern (to speed things along,
|
|
image capture was replaced by a 1/2 second delay at each point):
|
|
|
|
<iframe width="560" height="315"
|
|
src="https://www.youtube.com/embed/jO3SBandiUs" frameborder="0"
|
|
allowfullscreen></iframe>
|
|
|
|
It's still rather rough to use, but it worked well enough that I
|
|
picked up a [25mm M12 lens][25mm-lens] - still an angle of view of
|
|
about 10 degrees on this sensor - and set it up in the park for a test
|
|
run:
|
|
|
|
[{width=100%}](../images/2016-09-25-pi-pan-tilt-1/IMG_20160918_160857.jpg)
|
|
|
|
(*Later note*: I didn't actually use the 25mm lens on that shot. I
|
|
used a 4mm (or something) lens that looks pretty much the same, and
|
|
didn't realize it until later. It's a wonder that Hugin was able to
|
|
stitch the shots at all.)
|
|
|
|
The laptop is mainly there so that I can SSH into the Pi to control
|
|
things and to use [RPi-Cam-Web-Interface][] to focus the lens. The
|
|
red cord is just Cat 6 connecting their NICs together; the Pi is
|
|
running off of battery here. If I had a wireless adapter on hand (or
|
|
just a Raspberry Pi 3) I could probably have just set up a WiFi
|
|
hotspot from the Pi and done all this from a phone.
|
|
|
|
I collected 40 or 50 images as the stepper moved through the grid.
|
|
While I fixed the exposure and ISO values with raspistill, I didn't
|
|
attempt any bracketing for HDR, and I left whitebalance at whatever
|
|
the camera module felt like doing, which almost certainly varied from
|
|
picture to picture. Automatic whitebalance won't matter when I start
|
|
using the raw Bayer data, but for the first attempt at stitching, I
|
|
used only the JPEGs which already had whitebalance applied.
|
|
|
|
I stitched everything in Hugin on my desktop PC. I would like to
|
|
eventually make stitching possible just on the Raspberry Pi, which
|
|
isn't *that* farfetched considering that I stitched my first panoramas
|
|
on a box that wasn't much more powerful than a Pi. I also had to get
|
|
rid of some of the images because for whatever reason Hugin's
|
|
optimization was failing when they were present. However, being able
|
|
to look at Hugin's computed pitch, yaw, and roll values and see
|
|
everything lining up nicely with the motion of the steppers is a good
|
|
sign.
|
|
|
|
The first results look decent, but fuzzy, as $10 optics are prone to
|
|
produce:
|
|
|
|
[{width=100%}](http://i.imgur.com/zwIJpFn.jpg)
|
|
|
|
Follow along to [part 2](./2016-10-04-pi-pan-tilt-2.html).
|
|
|
|
[cs6475]: https://www.omscs.gatech.edu/cs-6475-computational-photography
|
|
[ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
|
|
[hive13]: http://hive13.org/
|
|
[makezine]: http://makezine.com/projects/high-resolution-panorama-photography-rig/
|
|
[scraptopower]: http://www.scraptopower.co.uk/Raspberry-Pi/raspberry-pi-diy-pan-tilt-plans
|
|
[steppers]: https://www.amazon.com/Elegoo-28BYJ-48-ULN2003-Stepper-Arduino/dp/B01CP18J4A
|
|
[raspi-spy]: http://www.raspberrypi-spy.co.uk/2012/07/stepper-motor-control-in-python/
|
|
[forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138
|
|
[raspistill]: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md
|
|
[RPi-Cam-Web-Interface]: http://elinux.org/RPi-Cam-Web-Interface
|
|
[25mm-lens]: https://www.amazon.com/gp/product/B00N3ZPTE6
|
|
[Hugin]: http://wiki.panotools.org/Hugin
|