I believe Marvel and DC have royalty thresholds. Back in 2014, DC changed theirs to a combined print and digital sales of 60,000 from 35,0000 print sales and to 5.4% of net revenue from of roughly 2% of the cover price.
http://www.bleedingcool.com/2014/07/...many-creators/
Image pays the creators based on sales. They pay no page rate. Plus Image only takes a flat fee. So once you make more than that fee and printing costs, you make money. It's up to the creator to pay his collaborators, if he/she has any, any rate. If your sales are low, you can pretty much make nothing. But with the flat fee and the price-per-unit, the more you sale the better the profit. Some creators like Scott Snyder, have said they make more money from decent Image sales than top selling Marvel and DC books.
http://www.jimzub.com/creator-owned-...anging-market/
http://www.bleedingcool.com/2015/06/...n-comic-books/
Breakdown of a mid-range Image book.