Click TIF, and the list should come up.

I have the light version on my Mac, too. Just press "save as" again. And then choose the file type. There should be a list of choices. There's TIF, PNG, JPEG and I think another one but I don't remember. But either PNG or JPEG you should click. If you can't find the list of choices, pm me.

The sketcher found on the site should be able to open a tif file. I use this format when I scan ensure the quality of the scan. If the sketcher can't then try downloading Gimp (It's available for Mac too), that may be able to as well. You can also try iaza.com, it should to able to convert it.

Note, I've not tried this, I have no tif files to work with right now.

the only thing I could think of is clicking save as and then giving your image a name like "myimage" but before clicking save add a .png or .jpg at the end of it.

So you would save your image as "Myimage.png"