Storing coins in 2×2″ slide trays

I’ve been using 2×2″ film slide trays to store my coins for a long while. I don’t know of many people doing this but they are suitable for most coins and can be acquired incredibly cheaply either second-hand or new due to the decline in usage over the past few decades.

coins in 35mm 2x2 slide trays

Recently I’ve started using 2×2″ lighthouse brand self-adhesive flips. I was previously using plastic envelopes but became concerned with the materials used and the possibility of corrosion of the coins. These flips are much better to work with and nicely seal the coins, as well as providing a good surface to label. The one downside is that it is hard to view the edge of the coins. Capsules would be nicer but their expense is something I can’t justify for circulation coins.

The slide trays are incredibly versatile, with lots of compatible storage options including drawers and briefcases. It’s a method that’s working well for me.

Alien Puma Space Train

Alien Puma Space Train (APST) is the name given to a community interested in the works of relatively unknown man named Daniel S Christiansen.

The fascination began after a photo gallery named “The Box of Crazy” was published on reddit’s /r/pics. The gallery showed numerous handrawn documents with a variety of technical, arcane, celestial and downright absurd content. The original posters found the documents in a wooden box in a basement. After much investigation by armchair detectives, the creator and original owner, who had passed away some years previously with no local relatives was found.

Daniel Christiansen's box

Although interest in the documents has dwindled, the first Alien Puma Space Train exhibition is now on in London, and I had the great fortune to make it there.

On the way to see the drawings

At the entrance we got a full page handout with background on the drawings, great for the uninitiated:

APST at the Horse Hospital

I won’t bore you with the details of my theories or background information, there’s a wiki where you can find out more:

I will say that the documents are far more impressive in person, the scale and attention to detail is quite remarkable. I really enjoyed getting up close with my personal favourite:

Text pages made for display

We arrived at the exhibition at the opening minute and had the place to ourselves. After about half an hour some London tour groups began to visit. APST is a pretty obscure topic, so I lunged at the opportunity to share my knowledge and ended up given an impromptu lecture on Daniel’s life, the discovery of the box and some of the theories regarding the drawings. It was my first chance to discuss the work in person and really enjoyable. I only wish some other /r/alienpumaspacetrain redditors had been able to come for a meet up.

As well as the videos, I’ve got a gallery of my images on imgur.

A Super Kickstarter


I’ve backed a few kickstarter projects now, such as the 3Doodler and Neverending Nightmares. They vary in their success, often with delays, there’s been a couple of complete failures. Recently I got a new set of books from the guys at Unlikely Hero Studios, who created the Super! comic book.

Blitz cosplay

I’ve decided it’s the more modest and artistic kickstarters that deliver best. And Super! has definitely been my favourite project to date. Some pictures from the latest books:

The guys at UHS have been fantastic and gone above and beyond in working with their backers. Especially international backers, who experienced delays as books were sent in batches to save costs. I got this awesome custom character sketch:

Blitz and Silhouette custom

Automatic Tank Recognition

A recent xkcd comic highlighted the varying complexity of tasks in computer science, and the unrealistic expectations that some might have using object recognition in images as an example:

xkcd 1425

Someone at flickr recognised this as a great opportunity show off some of their research.

I mention it because it reminds me of a great anecdote in the image processing/machine learning communities that I don’t hear often enough, here it goes-

The US government wanted a way to automatically detect tanks, for early warning or automated targeting. So a team of researchers went out and took 200 pictures of a variety of tanks. The next day they took 200 pictures without tanks.

They decided to use a neural network to teach their computer to recognise tanks. So in their training phase they gave it a picture of a tank, and told it there was a tank.

They gave it a picture without a tank and told it there was no tank. They repeated this with a hundred of each type, so the computer could identify tanks in a variety of circumstances – occlusions, colour, etc.

Then they gave it another picture from the remaining (unseen) images, and asked “tank or no tank?”. It got it right. They gave it another, and it got it right. It correctly classified all 200 unseen images.

This was a great achievement after a long period of research and significant funding.

Then to prove the versatility of the neural network, they started working with new images, with and without tanks.

The computer performed miserably, no better than random guessing.

Then someone noticed, in the original training set, the 200 pictures with tanks were taken on a sunny day, then 200 pictures without tanks were taken on a cloudy day.
They weren’t detecting tanks, they were detecting weather.

I’m not sure what the original source is, I was told the story at a BMVA event, but this appears to be the favourite telling:

It’s a great tale about the mysteries of neural nets, but also a tangential reminder that in image processing, computer vs human perceptions can be entirely different. There’s a lot of enthusiasm for replicating human vision systems, but it’s not the only option.

Technocamps Beachlab 2014

Aberystwyth Technocamps Beachlab 3D Printing Minecraft

Photo by Arvid Parry Jones

On Saturday Aberystwyth University held an “Access All Areas” event; opening the university up to the general public. As with last year we worked together to combine it with the Technocamps beachlab.

Aberystwyth Technocamps Beachlab 3D Printing Minecraft

Last year I got to demonstrate our relatively new 3D printing and scanning setup. This year things weren’t as exciting owing to some broken kit, but it was still a good day nonetheless. The recent news regarding 3D printing of gun components has clearly led to a major increase in awareness (some good, some bad). In many ways it was better that the machines weren’t in use as I got to had some in depth discussion with a variety of people.

Beachlab 2014 Dalek Doris

Aberystwyth Technocamps Beachlab 3D Printing Minecraft

Aberystwyth Technocamps Beachlab 3D Printing Minecraft

Photo by Arvid Parry Jones

A Nasty Hack for Image Landing Pages

I saw this on the Aberystwyth Comp Sci facebook group: It’s a little example of embedding image data within a HTML pae, in a similar (but less pleasant) way to using data URIs for embedding images stored as base64 strings (see below). It’s a very hacky way to give direct-link (rather than inlin/hotlinked) users a page rather than the image alone.

I was intrigued so took a quick look at the source and replicated it.

I don’t see much practical use, it’s ugly and I wouldn’t rely on it, but it’s straightforward to replicate and as the page states, all the magic is done client side.

Should work with most images (only tried with jpeg), the first few bytes (APP0 segment) go before the tag, that way it’s recognised as an image (we need to make the body hidden so that doesn’t show, then the page itself goes in the next few bytes – so we’re hoping the browser ignores these. Lastly we put the image data in an unclosed html comment. I suspect with a longer page we’d see the image becoming corrupt.

It even preserves exif.

So what’s the use? Well, you can use the same URL for the img src tags as you do for a landing page. But at the end of the day, you’re serving a corrupt page that shouldn’t work and can’t be relied upon.

It’s interesting, but the correct way to deal with hot linking, or image landing pages is to use mod_rewrite (in Apache). But at the end of the day, file extensions exist for a reason and you shouldn’t really be serving up binary data in such a messy manner anyway. There’s simply no point in forcefully redirecting users away from data like this; those that want it, will get it.

Here is an example of an image that can be copied and pasted directly as HTML. Many browsers recognise data URIs in which we can store data 9such as images as base64:

Where “XXXXXXXXXXXXXX” is the base64 string.

Base64 is a binary-to-text encoding mechanism that allows binary data to be transmitted as ASCII (a mere 127 printable characters) strings, when you see “MIME” referenced in relation to email, it’s about getting attachments added, and that’s how it works. Very roughly, encoding data as base64 (using fewer bits) increases size by a third.

Barebones Distance Function for pdist()

I had a bit of bother when adding my own distance function for use with Matlab’s knnsearch (and other functions). Surprisingly, custom functions aren’t discussed much and can be a bit troublesome the first time, so here’s the template I’m using from now on:


%Structure as specified by knnsearch.m:
% function D2 = DISTFUN(ZI, ZJ),
% taking as arguments a 1-by-N vector ZI
% containing a single row of X or Y, an
% M2-by-N matrix ZJ containing multiple
% rows of X or Y, and returning an
% M2-by-1 vector of distances D2, whose
% Jth element is the distance between the
% observations ZI and ZJ(J,:).

function [ L ] = distanceFunction(sample, models)
B = length(sample);

if size(models, 2)~= B
error('Mismatched vector lengths!');

model_count = size(models,1);
L = zeros(model_count, 1);

%compare the sample to each model
for m=1:model_count
model = models(m,:);
L(m) = 2.*(sum((sample.*log(sample+eps)) - (sample.*log(model+eps))));

I’ve left loops in for clarity, naturally, try and vectorise all that you can.

Also, eps is a useful function; it returns the distance to the next larger in magnitude floating point number. In most cases, you can take this to mean a really tiny number that prevents division by zero errors. A nasty but generally trustworthy trick.