I'm not ashamed to admit that this exercise was taken from Adobe's Tutorial site:

and modified by Alain Paradis

To make sure you are comfortable with this process, I will provide a few images. You will use this technique to make them high-quality bitmap images. We want to avoid too many broken lines, clogged dark areas and excessively white light areas.

You need to start by saving each image as a native Photoshop file.

Scanning Line Art

How to...

When scanning your image, you need to consider where you will use it. You need to scan it so that the pixels are as small as the smallest dot the printer can produce. We want to produce the image on the laser printers in the classroom. They are 600dpi printers. This means that we would scan the images at that resolution. This will ensure that lines will be smooth.

Scan the image in grayscale mode. You can scan the image as large as you want because you will be converting the image to bitmap mode once you are done.

The next step is to take make a back up of the original image by duplicating the "Background Layer". To do so, drag the layer's name to the "Page icon" at the bottom of the Layers palette.

We need to keep a record of the state of the image at the start. The easiest way to do this is to take a snapshot. Simply click on the camera icon at the bottom of the History palette. Name the snapshot "Unsharp Version".

While working on an image which is destined to be in bitmap mode, we should zoom to 100%. To do so, double-click on the "Zoom" tool. When you do so, your looking at each image pixel with one screen pixel.

Now we get to work. We need to emphasize the "edges" in the image — increase the contrast. The "Unsharp Mask" filter is the best tool to do so.

Go to the filter menu and select "Sharpen >Unsharp Mask". Set "Amount" to the maximum: 500. Select a radius between .5 and 5.5. You make the decision based on your image. Set "Threshold" to 2.

Click "OK". This has sharpened our image. Don't worry if this brings out roughness in the paper. The next step should get rid of it.

Now we're going to make our image look as if it was in bitmap mode.

At the bottom of the Layers, select the Adjustment Layers button, and select "Threshold". Threshold forces pixels which are darker than the number to turn black.

Most of the time, you can simply accept the number which appears in the dialog. If you don't agree, change them.

Now we have our image looking like a bitmap image. What we need to do is adjust any areas which either look clogged, have broken lines or have paper texture.

Increase shadow detail

Brush across the image with the Sharpen tool to bring out detail in shadow areas.

Fix broken lines

Use the "History Brush" with the mode option set to "Multiply" or "Darken" to make the lines thinner. Lower the Opacity settings if the changes are too extreme.

Reduce line thickness

Use the "History Brush" with the mode option set to "Screen" or "Lighten" to make the lines thinner. Lower the Opacity settings if the changes are too extreme.

Remove paper texture

Choose either "De-speckle" or "Median" from the "Filter >Noise" menu.

Control text thickness

If you have scanned text, you can make the text thicker by choosing "Filter >Other >Maximum". The terminology in this dialog is all opposite to logic. Just apply reverse logic to understand them.

Once you have refined the image, make sure there are no excessive white areas around it — that the canvas is not too big for nothing. You can use "Image >Trim" and check all the boxes. This should crop the image to its smallest practical size.

We are almost done. You have an image which looks like a good bitmap image, but it is still in grayscale mode. Simply go "Image >Mode >Bitmap". The resulting dialog will allow you to change the resolution. No damage will come to it, but you have scanned it at the right resolution and dimensions, so no change should be necessary. Click "OK".

Save the resulting image as a ".PSD" file, then "Save As" a tiff file. If you need to place it against a coloured background, save it as a "Photoshop EPS" file. The resulting dialog will give you the choice of making whites transparent.