With the image scanned in "Grayscale mode" and open in Photoshop, we will make adjustments to the image that will insure the sharpest line art image possible.

To increase the detail of the image, especially in the dark areas, the image will be sharpened using the "Unsharp Mask" filter. But before sharpening the image make a new Snapshot in the History palette. This will give us the option of going back to the original scan if needed and will help later in tweaking the image. To make a new Snapshot pick the "New Snapshot" option from the history palette's side menu bar. Give it a name so you can identify it later, I named mine UnsharpVersion. Now check the box just to the left of the new Snapshot so Photoshop will know to use that version when using the History Brush.