I have started participating in kimi's Kreative homework and learning a lot of new techniques. Many of the steps include changing the layer blend mode to mulitply, I know how to make the change, but what is it actually doing?

here is a link that describes it pretty well, I think

http://www.photokaboom.com/photography/ ... g_mode.htm

ps, you asked a question in making a frame thread that wasn't answer, I posted something there that I think will help

Kimi's homework is great; You'll soon know enough to be dangerous!

Look at this thread in the Helpful Links section...
viewtopic.php?f=16&t=1773

That link gives illustrated explanations of what every one of the blend modes does, not just multiply. I printed out that entire explanation so I can easily use it as a reference.

Rusty

The main purpose of the multiply mode is to darken, as explained in previous posts. Here are two common uses for it.
1 - Dark vignette. Let's say you want to darken the outer part of you image to make your subject stand out. Use the elliptical markee tool to select around your subject. Feather selection (50 to 150 depending on file size...). Invert selection. Copy to new layer (Ctrl J). Deselect. Change the new layer blend mode to multiply and vary opacity.

2 - Channels selection. You don't need additional add-ons to extract channels. Multiply can help you do it, because it works on every R,G,B channel. Let's say you want to extract the red channel. Add a solid fill adjustment layer with red in multiply mode. That's all.
Multiplying with red means multiplying reds on the underlying layer with 100% red (no darkening of reds), multiplying green with 0% green gives 0% green (black), same with blue. This means the green and blue components have been eliminated. This has filtered all but the red component of your image.

When you want to darken, you may want to test other modes, such as darken or color burn.