I've been working on a drawbot based on Eggbot and Sandy Noble's Polargraph for probably a year or so, if not more. I've finally cracked the accuracy problems that have plagued it for most of that time and the point where it became useful coincided with StippleGen being released by Evil Mad Scientist, able to produce beautiful stipple patterns for Eggbot and other plotters.

I've adapted some Processing code to run the stipple patterns StippleGen produces on the drawbot and today I tried a new trick - colour!

I wondered if running StippleGen on the CMYK channels of an image one-by-one might produce a colour image if I plotted them on top of each other.  Initial experiments seemed to indicate that it was promising:

I separated the cyan, magenta, yellow and black (key) channels and saved them as PNG for StippleGen to use as input.  I ran StippleGen to generate the stipple pattern and saved it as SVG after optimising the path to save plotting time.  A screen capture of the StippleGen pattern for each of the channels, converted into grayscale then merged into the CYMK channels in a new image showed the result above.

I found a set of felt pens that seemed to give a reasonable set of the four colours needed and ran the stipples one after another.  I had to pay attention to the paper - over-drawing four times could overwhelm paper that wasn't set up for it so I found a pad of Daler-Rowney Bristol Board, made for technical pens and airbrushes. Glossy inkjet paper would probably work also.

The Processing code I use makes filled circles with a spiral pattern that's reasonably quick to draw and I spent a while optimising the servo pen lift/drop speed - 4 channels with 2000 stipples each is 8000 dots, easily the largest plot I've yet done, end-to-end it took about 5 hours with each plot taking over an hour.

Here's the result:

The picture above didn't come out that well from my camera but I'm quite pleased with it in person, lots of kudos should go to EMSL for StippleGen - it has rapidly become one of my favourite Processing sketches.