Wkhtmlpdf graphics quality

Over time, I use wkhtmltopdf to generate PDFs. Everything is fine, except for pie charts drawn on the canvas.

I would add that the animation is disabled. Below is the wkhtmltopdf entry options. I've tried different DPI settings and image quality.

no-stop-slow-scripts = true, javascript-delay = 3000, image-dpi => 600, image-quality = 100, disable-smart-shrinking = true, lowquality = null

PDF:

HTML: