algorithmimagestroke

Painting stroke generation algorithm for robot arm

I am writing a code that generate start and end points of strokes of a picture (Raster images) to let robot arm paint.

I have wrote an algorithm but with too many overlapping strokes: https://github.com/Evrid/Painting-stroke-generation-for-robot-arm-or-CNC-machine

The input of my algorithm:

enter image description here

and the output (which is mirrored and re-assigned to the colors I have) with 50 ThresholdOfError (you can see the strokes are overlapping): enter image description here

Things to notice are:

*The strokes needs to be none overlapping (if overlapping then have too many strokes)

*Painting have different colors, the same color better draw together

*The stroke size is like rectangles

*Some coloring area are disconnected, like below only yellow from a sun flower: enter image description here

I am not sure which algorithm should I use, here is some possible ones I have thought about:

Method 1.Generate 50k (or more) random direction and position large size rectangles, if its area overlap the same color area and not overlapping other rectangles, then keep it, then decrease generated rectangle size and after a couple rounds keep decreasing again

Method 2.Extract certain color first then generate random direction and position large size rectangles (we have less area and calculation time)

Method 3.Do edge detection first, then rectangles are generated with direction along the edge, if its area overlap the same color area and not overlapping other rectangles, then keep it, then decrease generated rectangle size and after a couple rounds keep decreasing again

Method 4: Generate random circle, let the pen draw points instead (but may result too many points)

Any suggestions about which algorithm I should use?

Solution

  • I would start with:

    1. Quantize your image to your palette

      so reduce colors to your palette first see:

    2. segmentate your image by similar colors

      for this you can use flood fill or growth fill to create labels (region index) in form of ROI

      see Fracture detection in hand using image proccessing

    3. for each ROI create infill path with thick brush

      this is simple hatching you do this by generating zig zag like path with "big" brush width in major direction of ROI so use either AABB or OBB or PCA to detect major direction (direction with biggest size of ROI) and just AND it with polygon ROI

    4. for each ROI create outline path with "thin" brush

      IIRC this is also called contour extraction, simply select boundary pixels of selected ROI then you can use A* on ROI boundary to sort the pixels into 2 halves (or more if complex shape with holes or thin parts) so backtrack the pixels and then reorder them to form a closed loop(s)

      this will preserve details on boundary (while using infill with thick brush)

    Something like this:

    ROI

    In case your colors are combinable you can use CMY color space and Substractive color mixing and process each C,M,Y channel separately (max 3 overlapping strokes) to have much better color match.

    If you want much better colors you can also add dithering however that will slow down the painting a lot as it requires much much more path segments and its not optimal for plotter with tool up/down movement (they are better for printing heads or printing triggered without additional movements ...). To partially overcome this issue you could use partial dithering where you can specify the amount of dithering created (leading to less segments)

    there are a lot of things you can improve/add to this like: