This is probably really simple but I'm no PS expert. I have a grayscale layer in multiply mode. I want to 'flatten' it so that it makes the multiplication permanent and becomes a semi- transparent layer. All white pixels become 100% transparent and all 50% grey pixels become 'black' at 50% transparency etc etc. in 'normal' transfer mode. Thanks in advance
Well, you're on the path to expert status... Anyway, It sounds like you want Transparency to behave the same as Multiply, I don't think you'll be able to do that and achieve acceptable results.
Could you - Duplicate the PSD to create a stunt file, than flatten just the components that make up this Multiplied element - The multiplied layer and the target layer. Than, reinsert this prepared and flattened layer into your project?
Of course, you could do this within the original file. I just like to do stunts in another file. : )