Going retro: image dithering

Recently I have published the AmigaFFH on CRAN. This package allows you to read, write, interpret and modify Commodore Amiga file formats in R. This seems like a good opportunity to publish a small series about going retro in R. In this post I will show how to apply oldskool dithering techniques to images.

Back in the day home computers had limited memory and graphical capabilities. As a result images were usually stored and displayed using an indexed palette with only a handful of colours. When digitising photographs colour banding occurs due to this limited palette. This is why dithering was introduced. Dithering deliberately adds noise to an image to reduce colour banding when digitising photographs.

In this example I have used an image of the Amiga boing ball as an example. The technique requires two stages. First we need to a palette (first stage) to which the image needs to be dithered (second stage). The palette can be based on the original (true colour) image, or we can force our own palette to the image. In the first case we need a clustering algorithm to determine the most frequently occurring colours which can be used in a palette. In the second case you can pick any colour you like.

Below you see the result of both strategies. The top row selects a palette based on the original image, where from left to right, the number of colours are 4, 8, 16, 32 and 64. In the top row no dithering is applied. You can see how bands of different colours are formed, particularly for the low number of colours. In the middle row, you can see the same images, with the same number of colours, but in this case dither is applied. Even though the same number of colours are applied, the bands are much less apparent due to the dithering. Last, but not least, the bottom row show the same image where we force a black and white palette to the resulting image. From left to right, different dithering methods are used, each with slightly different results.

The source code for generating this image is, us usual, provided below. Note that dithering can be applied to any type of continuous information where the 'depth' is reduced (although currently not implemented in the package demonstrated here). For instance when reducing audio from 16 to 8 bit, dithering can be applied to prevent banding. In the coming month I would like to go retro some more. I will bring back pixels into your life by showing what the AmigaFFH and adfExplorer packages have to offer. And don't forget about the chiptunes which can be used in R using the ProTrackR package.

ProTrackR: chiptunes in R (part three)

It has been a while but I've made some small progress on the ProTrackR package. Many bugs are fixed and some functionality is added. This is making tracking in R more and more easy and fun. As if developing a package for handling ProTracker modules isn't the nerdiest thing ever, I found a way to top it off. What if I combine the ProTrackR package with a Shiny interface? Well, you'll get a basic online tracker.

For more information you can also read parts one and two on ProTrackR.

ProTrackR: chiptunes in R (part two)

A short follow-up on my previous post. I have just released a new version of the ProTrackR package (available on the CRAN). It can now actually play ProTracker modules, yeah! The routine isn't perfect yet but it does a decent job at the moment. The example below shows how you can download a module from ModArchive and play it:

ProTrackR: chiptunes in R (part one)

ProTracker is a popular music tracker to sequence music on a Commodore Amiga machine. As I still own a Commodore Amiga 500, I thought it would be a nice challenge to develop an R package that could handle ProTracker module files, and so I did. The first version of this package was just released on CRAN.

In this post I will briefly explain what ProTracker modules are and how they work. Then I will give a short demonstrations of the current sweetness the ProTrackR package has to offer. On this blog I will try to keep you updated on new versions of this package and its new features.

The module (MOD) is a computer file format used primarily to represent music. A MOD file contains a set of instruments in the form of samples, a number of patterns indicating how (which notes and effects) and when the samples are to be played, and a list of what patterns to play in what order.

The first release of the ProTrackR package contains the bare bones required to import and export such module files, and modify them any way you'd like (and the file format restrictions allow you to). This is a good time to start with an example. Let's start by loading the module 'Elekfunk' from The Mod Archive.

This module was used in a demo by Sanity to show off the Amiga's capabilities, which were impressive ate the time.

Playing routines in the ProTrackR package are currently limited to just playing the samples at specific notes (more fancy routines are in development). The examples below show how to play all samples in a module, a specific sample at different notes and applying different fine tunes. But at least you can export them as wave files.

Combined with the power of R, all kinds of fancy analyses become possible. The module for instance contains a sample of a guitar slide. In R we can now generate a power spectrum (which would have been tricky to do real time on an original chipset Amiga).

The power spectrum shows the shift in frequency which you would expect for a guitar slide. There are plenty other examples I could show you here but leave it at this for the moment. Hopefully you enjoyed these examples of the ProTrackR package, please stay tuned for updates on this package.