Careful what you wish for...understanding the math may not actually help you understand the aesthetic of using them. In general, for photo imaging, the basic ones such as screen & multiply, lighten and darken should be pretty easy to figure out. Overlay is a procedural blend of screen above 127 and multiply below 127 (middle gray does nothing). The others such as Luminosity, Color, Hue and Saturation should be self describing...
I think the better question (or questions) are what are the various blend modes good for. I really have no use for those other than what I've already mentioned...the others not mention may have some useful technical or mathematic use...but I don't find any use for digital photo imaging...
Understood. I agree, but I learned one or two interesting things by looking at Opgr's link from above:http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf#page=331
1) blending layers behave differently in a different color mode. I will need to experiment with this.
2) blending layers can be used to target only lighter or darker regions. I spend a lot of time with elaborate masking tactics to target certain ranges of luminosity or colors. Now I understand better how I can use lighten and darken blend modes.
3) I hadn't thought of using mostly blank layers with blend mode set to multiply, color burn, or color dodge and then painting in the blend mode effect with brushes--black or white, or a color I want to emphasize or de-emphasize.
In the past, my use of blend modes was mostly reserved to lighten for layered long exposure star shots, hard light for local contrast enhancement with a high-pass filter, and difference blending mode for finding the best seams when manually blending panoramics. What other interesting lessons about blend modes have I missed?