Create virtual brush stroke with bristle simulation and convert an image to a painting in a simulation way, adding brushstrokes until we get a satisfying result.

The idea is to simulate each individual bristle and to compose a paintbrush with bristles. We can then simulate brush strokes with various paintbrushes.

The interesting part of this project is the journey, not the result.

The project is currently a work in progress. There are many bugs to fix, and improvements to make. However, the project is already functional.

Debug

• Error with the initial direction of the paintbrush, need to clarify

Improvements

• VirtualBrushPP with C++ brushstrokes
  • Improve performance
• Rotation of the paintbrush (interesting for non disk shapes)
• Add more random to the bristle paint
• Make the painter more easy to use and interactive
• Automatic painter choices

inferno

original	paint

Searching for references on the internet to convert an image to a painting, the majority of methods I found used deep learning, transformers, etc. I thought it was a bit overkill for the task in question, and I thought that I would surely be able to do it iteratively by filling in a virtual paint.

My original idea was to be as close to a simulation of human interactions as possible. By learning about these methods, I noticed that only a limited number of brushes were used, and transformed. I thought it would be more interesting to simulate unique brushes.

While searching on this side, I discovered the impressive works of David Li: dli/paint. There is no way I'm doing something so good, but it was from him that I got the idea of simulating a brush from these bristles.

I started writing Bristle and Paintbrush classes. Each classes came with a construction (initialization) and two methods : next and draw. The next method compute the next position in function of the movement applied. The draw method return the coordinate that have been painted.

This part has not taken a lot of time to have results, and the results where satisfying. It takes me a little time to find a way to use Bézier curves control points to make it looks like a real bristle, but it was ok.

Now the real results will appear, I started working on a painter system which will place brushstroke to convert an image into a painting. The idea is to segment the image and to replace the segmented area with a brushtroke. Iterating on this process, I should manage to get a quite good results.

Will working on the painter, I got the following problem : test a new setup will take hours, and I cannot afford that.

As you can often hear "Premature optimization is the root of all evil". This is true, but in my case, I just don't see any other solutions than to improve the performance of the brushstroke generation.

My idea here was simple, use numba just in time compilation system to improve the speed of the function.

Using PyCharm profiling tool, I was able to detect which part of the code was the bottleneck. I started by redefining the Bézier curves and significantly improve their speed.

compute 1 000 000 bezier curve :

I continue to do improvement, using as much numba as possible, but in the end I has to accept two facts.

• Performance was still an issue, as the improved brushstroke performance was outweighed by the number of brushstrokes used by the painter.
• The code was getting harder and harder to read has I tried to limit the negative impact of python class call and merging functions.

Faced with these conclusions, my idea of solution was the following : I will split the project into two subprojects.

• VirtualBrush, with the python scripts and the painter
• VirtualBrushPP, a C++ implementation of the brushstroke simulation system with python bindings using pybind11.

🚧 I am currently working on this 🚧

A Paintbrush is composed of individual Bristles. Each Bristle is represented using Bézier curve.

🚧 TODO / WIP 🚧

A Brushstroke is a movement of a Paintbrush on a surface, applying paint.

🚧 TODO / WIP 🚧

A Painter is a specific algorithm which apply Brushstroke on a virtual paint, using an image as input.

The Painter rules will define the style of the painting.

🚧 TODO / WIP 🚧