In IMBLEND, opacity is just a scalar which controls the final composition after blending. For the simple case with no alpha content on the inputs:
out = opacity*resultfromblend + background*(1-opacity);
… or whatever is the conventional composition for the environment when alpha is present (e.g. SRC-OVER)
I really never could figure out what the intent was with those modes. That’s another reason I was interested in figuring out what used to be on the site. The developer clearly had his mind set on solving problems with the ‘softlight’ mode. I can only assume there was purpose behind these other modes. Some just seem so radical I can’t really even guess.
For what it’s worth, I don’t know that the renaming really clarifies things to that end. It’s kind of the curse of blend mode naming. The goals are often similar, but the english language has only so many ways to succinctly rephrase “make brighter/darker”. I have often entertained just using other languages simply for the latitude.
It’s all your choice in the end, but I’m reluctant to change names unless it better helps describe the math, the relationships between complements/transposes/inverses, or the characteristics which differentiate it from other modes of similar utility. I changed ‘parallel’ to ‘harmonic’ because that’s mathematically the more correct description,but I left the EffectBank modes as they were simply because I didn’t want to change conventions without confident reason on my part.
If you can figure out the intent, then we’re both better off, but ‘lighten’ and ‘darken’ at least need disambiguation. At least in the sources I found, EffectBank already had a unique non-relational ‘lighten’ and ‘darken’ mode anyway.