transparent-png

handy function for converting high-res whiteboard sketches to crisp, transparent background PNGs. Thanks for the wicked-awesome Marciana drawing, Monica ;)

Getting running

Super easy:

• clone this repo
• cd transparent-png
• pip install -r requirements.txt
• To test: python converter.py

Here's the result you should get:

Here's a more fully-feature version. This works best on whiteboard sketches where the target colors are very consistent, but the visual effect is cool nonetheless:

python converter.py --in_file ./balloons-over-bagan.jpg --out_file ./balloons.png --targets 182 109 58 121 29 39 103 118 77 --steepness 0.25 --offset 40

Takes you from this...

to this:

Tuning the conversion

I use a sigmoid function the looks at how dark a pixel is and, based on that, assigns it an alpha transparency. The sigmoid function is nice because it renders a smooth gradient against a transparent background, avoiding the awkward discontinuities that a simple threshold would create. The defaults I picked worked pretty well, but if you'd like to play with them this is the function you'll be adjusting:

--offset shifts the curve right and left, and --steepness controls the steepness of the transparency gradient. The larger this number, the closer your approximation to a strict threshold for transparency will be.