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Monochrome Thumbnails

Published on Sun, 28 August 2011

Ever since this version of my site went live I’ve been meaning to post about the generation of the monochrome thumbnails on the front page. When I was building the site I wanted to include recent items from my Flickr photostream. However with the predominantly monochrome design I didn’t like the look of all the colour they added. So I looked into having monochrome versions of the thumbnails shown.

The first thing I investigated was Javascript image processing libraries. The only main contender in that space was Pixastic. It worked but its cross browser support wasn’t great at the time. So I moved on to writing a tool that I could run locally.

I decided the tool should generate a single image with both the colour and monochrome versions in it (a technique known as spriting). Using a single image means only one HTTP request instead of forty. Being a programmer with an interest in Cocoa programming I created a small command line tool that used the Flickr API to get the details of the last twenty images in my photostream, fetch them and then use Core Image to convert them to monochrome, add both the colour and monochrome versions to the output image and finally save the result.

This worked great, however when I stopped hosting my site on my Mac I thought I would need to run the process periodically on my Linux server, which ruled out Core Image. I took this as another opportunity to learn something new and rewrote it in Lua using imlib2 bindings. I had to make some additions to the imlib bindings, which are published on GitHub.

I used the Lua version for some time but never bothered to set it up on the server. I wasn’t uploading photos all that frequently and it was simple enough to run locally and rsync the result. I’ve recently switched back to the Mac version as it was simpler to get up and running on my new laptop.

The code is on GitHub if anyone wants to do something similar. The Cocoa version is on the master branch, the Lua version is on the lua branch.

The current version of the processed thumbnails is shown below.

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