Python thermal printing library

Hello Lauri,
I really need your help. I want to print image with two graphs using thermal printer which is connected to Beaglebone black.
I did try with just random graph image from the internet, but resolution is bad, and color of the lines in the graph is grey. It is not clear. I also changed the graph line’s
thickness and got more clearer print, but still it is not clear enough.
How can I overcome this problem?
What should I need to do to get clear print from thermal printer?
I will be very glad for your help.