Bullet Time – Frozen Pi Reloaded

Last year we created Frozen Pi, a rig to re-create the frozen time effect made famous by the Matrix. This year it’s “Reloaded” and improved, premièring on BBC Four as part of the prestigious Royal Institution Christmas Lectures.

Update — if you’re in the UK you can watch the demonstration in the lecture on iplayer http://www.bbc.co.uk/iplayer/episode/b04w84yp/royal-institution-christmas-lectures-2014-sparks-will-fly-how-to-hack-your-home-1-the-light-bulb-moment?t=25m10s Watch out for the youtube link for the rest of the world in January.

Here’s an interview about the original rig:

We improved the hardware and the software, making the rig bigger, faster and snappier. We wanted to freeze people so they appeared to hang in mid air. Here’s a sneak preview from the rehearsal.

IMG_20141211_174249This year, the Royal Institution’s Christmas Lectures titled “Sparks will Fly; How to Hack Your Home” appealed even more to the engineer in me, as Professor Danielle George from The University of Manchester showed how anyone can use and adapt low cost technology to achieve extraordinary things. It was a great privilege to demonstrate the Frozen Pi rig at the Christmas Lectures, as for me and many families, they’re just as much a Christmas tradition as turkey, mince pies and outrageous knitwear. Setting the rig up, and standing in the centre of the famous lecture theatre, I did find myself thinking that Michael Faraday, father of electricity and creator of the lectures, must have stood on that very spot.

We made a number of improvements to last years rig including:

  • Custom CNC supports keep the rig level and at a sensible height
  • Faster shutter speed reduces motion blur
  • Migration to the excellent picamera Python package by Dave Hughes http://picamera.readthedocs.org/en/release-1.8/
  • Capture people full height with a larger arc – means subjects can be more energetic
  • Improved debugging information
  • Faster fetching of images
  • Replaced NTP syncronisation with network multicast for faster setup

Testing the rig last year, we didn’t know whether it would work until we actually pushed the button to try it. And this year, with the new software it was just the anxiety. Would it work?

IMG_20141211_184729Huddled in the backstage corridor preparing to carry the rig out in front of an eager audience of excited children, and potentially millions of TV viewers it was quite tense.

IMG_20141211_190044You’ll have to tune in on BBC Four at 8pm to find out if it worked. We’ll post a behind the scenes after the programme goes out.Paul Wilkinson Photography Ltd.

[Photo Paul Wilkinson]

Bullet Time Effect – Frozen Raspberry Pi

Some people said we were trying to build a Raspberry Pi time machine. In some ways they were right. Others compared it to the LHC at CERN and said we would warp time and space when they saw our pictures on Facebook https://www.facebook.com/raspberryPiFace. They were partly right too.

Raspberry Pi LHC

The Raspberry Pi Large Hadron Collider? It felt like we were building it.

And on the Friday night before the Jam it felt like we were building the LHC! With nearly half a kilometre of network cables, 48 Raspberry Pis fitted with cameras and PiFace Control and Displays we wondered if we’d finally been too ambitious with a project!

It started over 13 years ago watching when I saw the film The Matrix and a BBC documentary called Supernatural: The Unseen Powers of Animals. What linked the two programs was a camera effect where time would stop and the camera would move round the scene. I spent days trying to work out how the effect worked – I accepted that The Matrix used computer generated graphics, but surely the animals in a BBC natural history unit documentary had to be real? My faith in wildlife documentaries was reassured when I discovered a few years later how the effect was created.

The effect was called Bullet time, or Time-slice and consists of taking pictures from a long line of cameras at the same time, but playing them back one after another. Because all the frames are taken at exactly the same time, the action is frozen, but when the frames from cameras, each with a different view, are shown in order, it gives the effect of moving around a scene while time is frozen. On paper it seemed quite simple, to create a bullet time effect, you just needed a lot of cameras that would trigger in perfect sync. The camera rigs for TV and film are as impressive as the budgets, with tens of digital SLR cameras triggered by a slave cable. I could barely afford one DSLR camera, never mind twenty odd. Nor could I afford the tripods to mount them on! I thought my dreams of creating my own bullet time effect were simply unaffordable. That is, until I had an idea back in June this year.

Raspberry Pi Snap Camera

PiFace Snap-Camera turns the Pi into an easy to build simple digital camera

I’d been working on a PiFace interface so I could use my Raspberry Pi without a keyboard and monitor. For a bit of fun I wondered if I could turn it into a simple digital camera, that would take a picture when a button was pressed, and to my pleasant surprise, discovered you could. An idea was beginning to form in my head. If I wrote a bit more code, instead of pressing a button to take a picture, I could trigger it remotely over a network. Furthermore, it cost a lot less than any other digital camera. Could the Raspberry Pi really recreate a bullet time style effect?

I have various crazy ideas, but normally they subside after a few days, but this one wouldn’t. I decided to buy four Raspberry Pi cameras to see if I could trigger them all at once. I laser cut a frame to mount them and it appeared to work, but with four cameras I couldn’t really tell how good the effect was. I decided to buy another four cameras, with the justification that if it didn’t work I’d either sell the cameras or use them in workshops I did with young people. Eight cameras showed promise but nothing conclusive, there was only one way to find out.


Sometimes you wonder if a project was a bit too ambitious

It’s a funny feeling carrying nearly 50 computers in a box barely big enough to hold a laptop. In contrast, after multiplying the original mounting frame by 12, I’d ended up with a 3m wide circle. This was when I first realised I was building something significant. After much plugging, wiring, mounting, and SD card package installing the rig was finally ready. It certainly looked impressive, particularly given it was wider than the office. As such, the first time we tried the full rig was the Manchester Raspberry Jam.

I’d mentioned to Ben Nuttall, general star, (soon to be working for the foundation) and organiser of the Manchester Raspberry Jam that I’d be bringing the Frozen Pi rig, but for some reason he didn’t automatically associate this with a 3m ring of 48 Raspberry Pis, half a kilometre of network cable, a few industrial network switches and enough power adapters to terrify most caretakers. We were generously squeezed into a corner of Madlab at the capacity jam.

A packed Manchester Raspberry Jam

A packed Manchester Raspberry Jam

Soon pictures of the rig were being posted on Facebook and Twitter, yet still we hadn’t actually tested the full rig. The first eager volunteer bravely strode into the circle. We pushed the button and the red camera lights came on in unison. A few moments later the first images had been collected over the network and were being stitched into a video. To everyone’s amazement, including mine, it actually worked! Raspberry Pi had frozen time, recreating a Hollywood effect for a fraction of the cost. You can see the results in the video above http://youtu.be/IqoA4HeBCQ4?t=2m19s

The setup wasn’t perfect – the floor in Madlab is characterful and the rig was a bit low, which meant sadly we chopped Liz Upton’s head off when she had a go. Despite this, we showed it was possible. We’d learned a few things along the way –booting and installing software on 48 Raspberry Pis needs a bit of work, and the PiFace Control and Display proved essential for debugging by showing what was going on, and allowing us to push switches to trigger actions and see status without plugging in a monitor.


Our patented support system was perhaps a bit low

The navigation switch on PiFace Control and Display allows us to set the index of the camera in the rig, so it makes it easy to build the rig in different shapes.

The rig generated a lot of interest and hopefully, in line with the aims of the Raspberry Pi foundation, has inspired youngsters to code and shown the computers can be used creatively.  I could imagine an after-school club building their own rig with a class set of Raspberry Pi and cameras.

For those with just one Raspberry Pi, its still possible to play with time. Instead of freezing it with the bullet time effect it’s easy to speed it up with a time-lapse as shown in the previous blog post.

We’ve still got a few tweaks to make to it, but we’ve got loads of things plan to shoot with Frozen Pi. We’re looking for suggestions too! If you’ve got an idea, or want to see more videos get in touch via our Facebook page.

Tech Specs

For those of you interested in the gory techie details, here are the stats

  • 48 Raspberry Pi Model Bs
  • 48 Raspberry Pi Cameras
  • 48 PiFace Control and Display
  • 48 NOOBS SD cards
  • 48 5V PSU
  • About half a kilometre of network cable
  • 2 x 24 port switches
  • 1 wireless router
  • Custom laser cut frame
  • Enough extension cables plugged into a single socket to scare most caretakers
  • Python script listening to receive command to take picture (included in snap-camera package) https://github.com/piface/snap-camera
  • Python script to collect images over network and assemble frames in order

Timeslice is a trademark of Time-slice films and Bullet time is a trademark of Warner Bros.

Raspberry Pi Time-lapse – in the field!

Finding myself shivering in a field I wondered what else this credit card sized computer would be responsible for.


I was testing my new time-lapse setup with Raspberry Pi, a camera and PiFace Control and Display. When I do talks to teachers about why they should use a Raspberry Pi I point out you can put it in places you couldn’t put a PC, and I was certainly following my own words as I trekked up a hill overlooking Manchester. I’d previously tried pre-programming a Raspberry Pi that I could leave on a hillside to take pictures, but found I needed to change settings in the field. Taking a keyboard and monitor out with me was impractical, and sometimes it was hard to know if the Pi had started taking pictures.

Youtube compression isn’t great and doesn’t do justice to how reasonable the Raspberry Pi camera is.

Using PiFace Control and Display I could easily set the time between pictures and how long the time-lapse should cover. This is useful as often before I start taking a time-lapse I don’t know how much I want to speed the action up by, or how long to keep taking pictures for until I’m ready to start taking them. The display shows when the camera has started and how much room there is left on the SD card. It makes it really easy to take time-laspse with the Raspberry Pi. So much so I think I’m addicted!

The software is really easy to install – just type

sudo apt-get update

sudo apt-get install python3-snap-camera

There’s a quick video walking though setting it up from scratch and showing another time-lapse in the city centre.

It’s opensource and available on github, so hopefully between us and the community we’ll get more settings for the camera added. We’re also wondering about re-writing it to use Dave Jones’ python libraries for the Raspberry Pi Camera, or adding features like scheduling the time-lapse to start at a particular time.

For more info on things to do with PiFace visit our guides http://www.piface.org.uk/guides

Win a signed copy of the book Raspberry Pi Projects with PiFace Control and Display

Enter our PiFace Control and Display Advent competition to win a signed copy of the new book, Raspberry Pi Projects.

We want you to create an application with PiFace Control and Display that counts down until Christmas (or any other day you prefer). It couldn’t be easier to get started – we’ve posted some sample code https://gist.github.com/thomasmacpherson/7684150  that you’re free to edit and remix. Once you’ve made your project, post a picture/video/link on our Facebook page http://www.facebook.com/raspberryPiFace  and upload the code onto github.

Even if you’re new to coding and don’t feel ready to add complicated features, you can still enter by editing the festive graphics (they’re stored as bitmaps of 1s and 0s at the top of the program).

You might want to make your calendar interactive – revealing an icon of the day, or perhaps add sound effects. You could pull in data from the Internet, such as incorporating a Santa tracker showing how far away he is from, or showing the chances of a white Christmas with weather data.

Useful chunks of sample code are available in the guides http://www.piface.org.uk/guides/  section of the website.

Raspberry Pi Projects Book

The most creative and innovative entries will win a signed copy of the new book, Raspberry Pi Projects. We’ll also consider when you entered – so get your idea in early to be the first. Don’t forget if you can’t wait until after Christmas to get the book, you can also order it from Amazon!


Entries must be posted on Facebook page by 2359 GMT 24th Dec. Entries will be judged on creativity, innovation, fun and technical execution. The judges’ decision is final and no correspondence will be entered into. All entries must be your own work. Winners will be contacted by Facebook message and prizes will be sent by post as soon as possible after the closing date. Winning entries will be featured across social media sites.

Website Launch

I’ve just pushed the button to update the DNS around the Internet so in a few hours time our new website should go live. It’s been a lot of work, but we’re nearly there now. No doubt there’ll be bugs in it and we’ll tweak as we go, but once the infrastructure is in place, we can start uploading our tutorials. When the site goes live, this blog will have moved to http://www.piface.org.uk/iblog/

A new Arrival in the PiFace Family

Those of you who are friends of PiFace on Facebook https://www.facebook.com/raspberryPiFace will have learned yesterday about PiFace Control and Display.

The result of about 10 months work, it’s a very easy to use LCD screen with buttons for the Raspberry Pi. The idea for it came from wanting to get more people using Raspberry Pis. The small size and low cost of a Raspberry Pi mean that you can put it where you wouldn’t put a normal PC. In my case, I’d been using it to monitor wildlife in a remote part of Wales. Although the Pi is credit card sized and low powered,  monitors and keyboard aren’t.

PiFace Control and Display was designed to show the status of a Raspberry Pi without having it plugged into a monitor. It also has buttons that can be used to drive a menu so it is possible to interact with it.

I’d had the moment of inspiration when I wanted to build an Internet radio with the Pi to listen to. Obviously I didn’t want a big screen and keyboard so I came up with Control and Display. To make it even easier to control I added an infra-red receiver so I could change station from across the room!

Element14 interviewed me about it here:

I realised that there’s a whole raft of applications that need a way of controlling a Raspberry Pi and showing a brief status on the screen, and it was a great way to encourage youngsters.

As such, it was key to make it as easy to install as possible, and easy to program in Python. It’s one line to install, and two lines of Python code to print a message to the screen.

I’ll post over the next week more details.