can't get Unsharp Mask to work

I'm trying to use Unsharp Mask in Photoshop Elements on an image that I scanned and can't get it to do anything. It won't even show a preview of the image when I pull down the Unsharp Mask menu. If I apply the mask, it doesn't appear to do anything, regardless of the mask settings.
What in the world am I doing wrong?

Thanks in advance,
Tom

Just curious, what is the size (xxx pixels by xxx pixels - NOT file size) of the image? And how much ram does your computer have?

Rad

One thing I do once in a while, without noticing, is that I may have accidentally clicked the magic wand on part of an image, but it's so small (with low tolerance and all), that you don't notice that it's selected. It'll apply the USM...but only to that section. Same goes for any type of selection tool.

Be sure that you don't have an active selection that you aren't aware of, or that you aren't viewing a layer other than the one you are sharpening.

That happens alot with me. I'm woking on a picture applying levels/curves and such and forget to select a top most active background (image) layer.

Aha! I think I may have found the problem - on my Layers palette, it appears that I had a Brightness/Contrast layer "selected" and not the "Background" layer - I think I've got it working now.
However, I thought I was supposed to sharpen the image at the end of my editing process. So, do I have to always go back to the "background" layer to do it? What do you all do?

Thanks for pointing me in the right direction.

Tom

Ideally, you should save your unsharpened "master" image as a PSD or TIF file with all the layers intact. Then, when you decide what you want to do with your image (print it or put it on the web, for example), you would flatten the image, resize (if necessary), then do your sharpening. Save your "new" image under a different name, or at least in a different location, so that you still have your master image available for more tweaking in the future.

Tom - what I always do, is make a copy of the background layer. I use adjustment layers for anything that can be done like that (Levels, channel mixer, curves, etc). Any other changes, some people will copy and paste affected areas into a new layer, but to be honest, I save as I go, so don't do that.

Many of my images end up with 4 layers (Background, Duplicate Background - where the edits happen, Channel Mixer adjustment layer, Levels adjustment layer)

Thanks for the responses, guys.

Tom