layer option 'multiply' to remove color to transparency

as an alternative to using the magic wand to remove a color to transparency (which leaves fine detail, say in a line drawing, in a very sorry state) i saw someone use the multiply function in layer options to remove all white from a greyscale image leaving black lines over transparency. neat, i thought. until i came to try it myself. does anybody know this trick?
gratefully...
fazz

Multiply works almost opposite of screen. Multiply darken colors at the same time blends or rejects lighter colors, while in screen it rejects dark colors...something like that

The best way to get the hang of the layer options is to just try them out for yourself. Multiply/Screen is good when you want to keep your extreme colors (like having black still show up when using Multiply); however, there are other layer options that allow for transparency effects. I use Overly as well as Color Dodge/Burn a lot. You can also try changing your layer opacity settings as well in conjunction with the layer options.

If worse comes to worst, you can always work with a layer mask, but it can be quite tedious, especially when working with antialiased layers that have dramatic color shifts.