Sunday, January 31, 2010

Visualizing RGB

Update: See the follow-up post here.

Aldo Cortesi posted a link today to, a site dedicated to images visualizing the RGB colour space - in particular, 4096x4096 images that use each RGB value exactly once. Inspired by his hilbert curve visualization and the urge to spend a day programming, I present to you: the all-RGB Mandelbrot set.

Sort by colour...

My idea was this: instead of trying to visualize the colour space directly, why not use a base image for the "shape", and then map the RGB spectrum onto it? I thought that if I could find an image with an even spread of colours, this would let me make each pixel unique yet keep the overall look untouched.
To perform this mapping, I chose to define an ordering based on the 3 dimensional Hilbert curve. Cortesi explains it far better than I can, but the basic idea is this: the Hilbert curve can be used to find an ordering of all 16.8 million colours so that if you were to stretch them out on a line, every colour would be there and they would flow smoothly from one to another. Like this, except a lot smoother and a lot longer.
With this ordering in hand it is easy to find the index into this line for each pixel in the source image, sort the pixels, and then assign them the colour they line up with.

Choosing an image

When I started this morning, I had the idea that the output images would look reasonably close to the source images. I was half right; the images certainly have all the same features as before, but the colouring is all wrong. In hindsight the reason is obvious - unless the original had a perfectly even spectrum of colours, the mapping would be stretched in some places and shifted in others, and in general not line up nicely.

While interesting, this wasn't exactly what I was going for. Hmm...what image could I use where it wouldn't matter if the colours were all shifted? The first thing that came to mind was a visualization like the Mandelbrot set, where the colours are arbitrarily chosen anyways. A quick Google search found me this:

Which, when transformed, came out as this:


I created all the visualizations here using Python 2.6 and the Python Imaging Library. It isn't the most efficient code (it takes half an hour to render a 4096x4096 image), but the quick development time easily makes up for it. If anyone is interested in playing with it, I have placed the code on github. Or if you just want to see what something would look like, feel free to send it to me and I'd be happy to run it for you.

Saturday, January 30, 2010


This blog has moved! It now lives at As is probably obvious, I have also changed the name to The Lowly Programmer (see the updated about me for details). Nothing else is changing at the moment; in particular, I doubt I will be posting to it with any regularity yet :).

Saturday, January 16, 2010

The value of a point

Recently I have been spending a lot of time on Hacker News. I've lurked for quite a while, but it is only in the last month or so that I have actively started to comment. I usually try for informative comments rather than going for the inflammatory or popular topics. This only gets me a point or two per comment I post, but these are points I have earned by contributing to the discussion in a positive way. I had almost reached 50 points this morning and was feeling quite good about my contributions overall.

But then I made a submission.

Most of my submissions go the way of my comments, earning with a point or two plus some interesting responses. It's these responses I am after; I find an interesting article somewhere, so I submit it to see what the HN community has to say about it. But this one, for whatever reason, the community really appreciated, and within 20 minutes it was at the top of the front page. The discussion was lively and as interesting to read as I could hope for, and it was raking in the points.

And therein lies the problem. Someone, a self proclaimed member of HN no less, took the time and effort to write a thought provoking piece and there I was earning scores of points off it, which left me feeling like a bit of a cheat. But even had I been the original author, I don't think I would want that many points for it. By the time it falls off the front page it will likely be over 50 points itself, surpassing a month's effort in one fell swoop and devaluing the points accordingly. I was looking at points as a general reflection of my value to the site, but I cannot do that anymore, at least not directly.

So what can be done about the 'problem' with points? I can think of a few suggestions.

  1. Nothing. After all, I am only a single opinion, and the system seems to be working fine as it is.
  2. Don't count any points past a certain cutoff. They would still be useful for display and ranking, but for karma the extra would be discarded. I kind of like this idea, but any cutoff would be an arbitrary one. Stack Overflow uses a system like this, although there it's points per day rather than per action.
  3. Count points on a log scale. Display them as normal, but change the way karma is calculated. This would help address crazy outliers like this one, and in general promote sustained quality over hot-button topics (for people actively trying for points).
I know pg is always tweaking the system to make it work better; it will be interesting to see what, if anything, actually changes in the next while.