As far as I know, they were an Adobe invention. Might not seem like it now, but Adobe did at one time have a pretty massive and respectable graphics R&D team wh

As far as I know, they were an Adobe invention. Might not seem like it now, but Adobe did at one time have a pretty massive and respectable graphics R&D team who invented so many things that we take as standard now. The formulas were reverse-engineered elsewhere, but not perfectly (Macromedia Fireworks and GIMP's blend modes did not behave the same way). As far as I know, the exact formulas were first documented in the PDF Specification v1.4 by Adobe: https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.4.pdf#page=436 https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandard... . At the time, this was an ISO specification and not freely available. Also, the formulas for Color Burn and Color Dodge in this specification have some bugs which don't match Adobe products. These formulas have since been copied into the SVG standard (which Adobe co-authored), and the CSS blend mode standard (which Adobe co-authored), where the bugs are now fixed. Porter-Duff compositing was more of a general theory for compositing A on top of B with a mask C, and the operators defined in their paper were the 3-way truth table of those bits. It only defines coverage, not the underlying color.