Articles by Simon Barthelme

Stippling and TSP art in R: emulating StippleGen

July 24, 2017 | 0 Comments

Stippling is the creation of a pattern simulating varying degrees of solidity or shading by using small dots (Wikipedia).StippleGen is a piece of software that renders images using stipple patterns, which I discovered on Xi’an’s blog a couple days ago. StippleGen uses an algorithm by Adrian Secord (...
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Superpixels in imager

March 24, 2017 | 0 Comments

Superpixels are used in image segmentation as a pre-processing step. Instead of segmenting pixels directly, we first group similar pixels into “super-pixels”, which can then be processed further (and more cheaply). (image from Wikimedia) The current version of imager doesn’t implement them, but it turns out that SLIC superpixels ...
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New version of imager package for image processing

March 15, 2017 | 0 Comments

A new version of imager is now available on CRAN. This release brings a lot of new features, including a whole new set of functions dealing with pixel sets, better support for videos, new and faster reduction functions. The most significant change is the introduction of a “pixset” class, which ...
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vecpack: an R package for packing stuff into vectors

September 18, 2016 | 0 Comments

Here’s a problem I’ve had again and again: let’s say you’ve defined a statistical model with several parameters. One of them is a scalar. Another is a matrix. The third one is a vector, and so on. When fitting the model the natural thing to do ...
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New features in imager 0.30

September 13, 2016 | 0 Comments

imager is an R package for image processing, based on CImg. This new release brings many new features, including: Support for automatic parallel processing using OpenMP. A new S3 class, imlist, which makes it easy to work with image lists New functions for interactively selecting image regions (grabRect,grabPoint,grabLine) ...
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New features in imager 0.20

May 2, 2016 | 0 Comments

imager, an R package for image processing, has been updated to v0.20 on CRAN. It’s a major upgrade with a lot of new features, better documentation and a more consistent API. imager now has 130 functions, and I myself keep forgetting all that’s in there. I’ve added a ...
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New R package for Eyelink eye-trackers

February 23, 2016 | 0 Comments

Eyelink eye-trackers output an avalanche of disorganised crap. I’ve written an R package that will hopefully filter that crap for you. It’s called eyelinker and it’s on Github. It outputs a set of dataframes containing raw traces, saccades, fixations and blinks, meaning it’s easy to produce ...
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imager now on CRAN, and a non-linear filtering example

September 17, 2015 | 0 Comments

imager is an R package for image processing that’s fairly fast and now quite powerful (if I may say so myself). It wraps a neat C++ library called CImg, by David Tschumperlé (CNRS). It took quite a bit of work, but imager is now on CRAN, so that installing ...
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New package for image processing in R

June 5, 2015 | 0 Comments

I’ve written a package for image processing in R, with the goal of providing a fast API in R that lets you do things in C++ if you need to. The package is called imager, and it’ on Github. The whole thing is based on CImg, a very nice ...
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cMDS: visualising changing distances

November 11, 2013 | 0 Comments

Gina Gruenhage has just arxived a new paper describing an algorithm we call cMDS. Here’s what it’s for: if you do any kind of data analysis you often find yourself comparing datapoints using some kind of distance metric. All’s well if you have a unique reasonable distance ... [Read more...]

ECVP tutorial on classification images

August 30, 2013 | 0 Comments

The slides for my ECVP tutorial on classification images are available here. Try this alternative version if the equations look funny. (image from Mineault et al. 2009) The slides are in HTML and contain some interactive elements. They’re the result of experimenting with R Markdown, D3 and pandoc. You write ... [Read more...]

Fitting psychometric functions using STAN

August 19, 2013 | 0 Comments

STAN is a new system for Bayesian inference, similar to BUGS and JAGS. I’ve played with it a bit and it’s quite promising, it really has the potential to make MCMC less of a pain (on simple models). I’ve written a short introduction to fitting psychometric functions ... [Read more...]

Predicting spatial locations using point processes

June 25, 2013 | 0 Comments

I’ve uploaded a draft tutorial on some aspects of prediction using point processes. I wrote it using R-Markdown, so there’s bits of R code for readers to play with. It’s hosted on Rpubs, which turns out to be a great deal more convenient than WordPress for that ... [Read more...]

Finding patterns in time series using regular expressions

May 17, 2013 | 0 Comments

Regular expressions are a fantastic tool when you’re looking for patterns in time series. I wish I’d realised that sooner. Here’s a timely example: traditionally, when you have two successive quarters of negative GDP growth, you’re in recession. We have a quarterly GDP time series for ... [Read more...]

Barycentric interpolation: fast interpolation on arbitrary grids

March 6, 2013 | 0 Comments

Barycentric interpolation generalises linear interpolation to arbitrary dimensions. It is very fast although suboptimal if the function is smooth. You might now it as algorithm 21.7.1 in Numerical Recipes (Two-dimensional Interpolation on an Irregular Grid). Using package geometry it can be implemented in a few lines of code in R. Here’... [Read more...]

Interactive MDS visualisation using D3

January 8, 2013 | 0 Comments

Here’s a sneak peak into upcoming visualisation work. I’ve been working a bit on MDS (Multi-dimensional scaling), a classical technique for visualising distance data. Classical MDS is useful, but interactive MDS is *much* more useful. Using D3, a Javascript visualisation framework, it’s relatively easy to make interactive ... [Read more...]

French R Conference in Lyon – call for contributions

December 12, 2012 | 0 Comments

[of interest mostly to French and R bilinguals] La prochaine édition des Rencontres R aura lieu à Lyon en Juillet prochain. Ci-dessous, l’appel officiel à contributions. ————————————————– Appel à communication des 2èmes Rencontres R : Dans la lignée de la conférence internationale Use’R et suite à la première édition qui a ... [Read more...]

edply: combining plyr and expand.grid

November 30, 2012 | 0 Comments

Here’s a code snippet I thought I’d share. Very often I find myself checking the output of a function f(a,b) for a lot of different values of a and b, which I then need to plot somehow. An example: here’s a function that computes the ... [Read more...]

New book: “Modeling Psychophysical Data in R”

September 14, 2012 | 0 Comments

Ken Knoblauch wrote to inform me that Springer has just released a book he coauthored with Larry Maloney on statistical methods in psychophysics. The book is called “Modeling Psychophysical Data in R” and covers both classical psychophysical analyses (Signal Detection Theory) and more recent methods (e.g. Mixed Models). Ken ... [Read more...]
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