I have converted a Nook book to an epub to display on my Kindle PW2 using duokan. The book contained many images of symbols (b/w line drawings). All the images on the Nook app on my android tablet look fine, sharp with good contrast. The generated epub on the Kindle displays the images as very fuzzy and faint, sometimes hardly discernible.

Is there a way to preserve the high image quality in Calibre during the conversion process?