blend mode numbers and their functions
-ei 0 ") alpha"
-ei 1 ") normal.mix"
-ei 2 ") add"
-ei 3 ") multiply"
-ei 4 ") substract"
-ei 5 ") screen"
-ei 6 ") darker"
-ei 7 ") lighter"
-ei 8 ") difference"
-ei 9 ") average"
-ei 10 ") negation"
-ei 11 ") exclusion"
-ei 12 ") overlay"
-ei 13 ") hard.light"
-ei 14 ") soft.light"
-ei 15 ") color.dodge"
-ei 16 ") color.burn"
-ei 17 ") reflect"
-ei 18 ") glow"
-ei 19 ") stamp"
-ei 20 ") freeze"
-ei 21 ") heat"
