WeasyPrint: Not defining the document encoding can be slow when chardet is installed

I have a 9 pages sized pdf document which includes 5 images. those 5 images are included via base64 encoded sources inline.

• When i exclude those images during the rendering, the entire pipeline takes about 16seconds.
• When i include those images, i end up with 49 seconds.

That’s a fairly big hit performance wise - are there any tools to optimize this at all? You find the PDF attached - it is not really complex but more or less is test document for our print.

We are using weasyprint using a REST api like this

@app.route('/pdf', methods=['POST'])
def generate():
    name = request.args.get('filename', 'unnamed.pdf')
    app.logger.info('POST  /pdf?filename=%s' % name)

    html = HTML(string=request.data)
    document = html.render(stylesheets=[CSS('css/local.css')], presentational_hints=True)
    pdf = document.write_pdf(zoom=0.7936507936507937)

    response = make_response(pdf)
    response.headers['Content-Type'] = 'application/pdf'
    response.headers['Content-Disposition'] = 'inline;filename=%s' % name
    app.logger.info(' ==> POST  /pdf?filename=%s  ok' % name)
    return response

This whole service runs on an developer machine (linux desktop) under docker

• Intel® Core™ i7-8565U CPU @ 1.80GHz
• with 32GB ram
• very fast m2 SSD

I would have expected it to be quicker then that, but it seems those images have a huge impact