Poor quality with Wand convert function (Python)

Question

I'm using Wand to the first time with Python in order to convert a PDF file into a JPG file, then apply a good recognizion script with OpenCV.

But, when I converted PDF -> JPG, the quality is really ugly. Font is not clear and I don't find a way to do that perfectly.

PDF file looks like :

The result given by my code looks like :

Finally my very little script (I just need to convert for the moment) :

#-*- coding: utf-8 -*-

from wand.image import Image

with Image(filename="/Users/test/Desktop/arrow.pdf") as img :
    img.save(filename="/Users/test/Desktop/PDF_to_JPG/arrow.jpg")

==> I miss an option ? I tried to change the size with img.resize option but none effect.

Thank you by advance