It is very difficult to find the information about algorithms of blend modes in the Internet.  pegtop.net and the blog by Andrey Zhuravlev in LiveJournal - two sites where I found the most detailed and the helpful information. Below is the fragments of the code for additional blend modes for paint.net written on the basis of the analysis of information from the websites shown above. All modes have been tested on similarity with blend modes of the Photoshop. In most cases results had the full coi