inkdrop

inkdrop is an artsy bitmap to vector converter controlled via a GTK4 or web UI.

Command line interface

The CLI binary is called inkdrop-cli and reads almost any image bitmap format via the --input parameter and outputs an SVG document given by the --output parameter. Let's take this image of the Nefertiti bust, cropped and the background turned to pure white:

Using the --draw-points parameter we can output all sampled points. The number of sampled points can be controlled with the --num-points parameter. Calling

$ inkdrop-cli --input nofretete.png \
              --svg output.svg \
              --draw-points \
              --num-points 20000

gives us

It resembles the input image but due to the stochastic nature, it is a bit noisy. We can move these initial points using the Weighted Voronoi method. Using

$ inkdrop-cli --input nofretete.png \
              --svg output.svg \
              --draw-points \
              --num-points 20000 \
              --voronoi-iterations 100

we get points that much better reflect the structure of the original image:

By leaving out the --draw-points parameter, all points will be connected. Without further adjustments the nearest neighbor tour is chosen which will be ugly most of the time because the path crosses itself. To fix that use the --tsp-improvement parameter which optimizes the tour using the 2-opt algorithm until the improvement is not better than the parameter given. So our final command line

$ inkdrop-cli --input nofretete.png \
              --svg output.svg \
              --num-points 20000 \
              --voronoi-iterations 100
              --tsp-improvement 0.001

gives us the following output:

gcode conversion

To create gcode ready to send to your drawing machine, you need to execute two steps:

• Use inkdrop-cli with the --json option (which will in addition to the SVG write a point list in JSON format as well)
• Use gcode-converter with the resulting JSON and a calibration file.

The calibration is derived from the measurements of your individual machine. A file looks like this:

{
  "base_width": 300.0,
  "base_height": 560.0,
  "drawing_width": 300.0,
  "drawing_height": 450.0
}

Now use this to call the CLI:

$ gcode-converter --calibration calib.json
                  --input nofretete.json
                  --output nofretete

which will create N gcode files in directory nofretete, where N is the number of channels of your picture.

Important: The gcode coordinates assume the home position (0, 0) to be in the center of the drawing area, so the origins of both coordinate systems are equal. In practice, this means:

• position in the center of the drawing area
• position the pen in the center of the paper
• reset the positions in your controller (reset to zero)

GTK4 user interface

Call inkdrop-ui and play around with the same parameters as above.

Web user interface

The web crate contains a web app based on Yew with a demo hosted here. Run make and serve the content with a server of your choice. python -m http.server could be a simple option.