Basic Levels question

Hello

I am pretty much a novice a PS, and so excuse my ignorance.

I use smart sharpen to sharpen my images and smart sharpen only works on a background layer, how can I apply smart sharpen to a background layer and then add a mask to erase some of the parts of the image I do not want sharpened?

Many thanks

Are you sure you can only apply sharpening to the background and not to other image layers? If that's the case, then one way to get around that is to create a duplicate image of what you are working on and then flatten the duplicate. You can then apply smart sharpen to tha flattened image, copy it and then paste it as a layer in the original image you are working on. You can then use masks, opacity, etc. to control the layer.

BTW, did you also have a basic levels question (as noted by your topic title)?