Scanning Tips: How to Scan Black and White Line Art
The Best Methods for Getting Crisp, Beautiful Scans of Your Black and White Line Art
by Paul Ace Diamond "Huggy" Blow
Scan as black and white bitmap
The easiest and fastest way to scan black and white line art is to scan it as "black and white line art" in your scanner software settings. For print purposes you should scan the art at 1200 dpi (or at LEAST 600 dpi if your computer or scanner can't handle 1200 dpi), and scale it to the size it will be printed as. For example, if your art is 11" x 17" and it will be printed in a typical 6.625" x 10.25" comic book, you would scan it at 1200 dpi at about 60% scale. Most scanning software programs have only one adjustable setting for scanning black and white line art: the "threshold" or "brightness" setting, where you can adjust how "bright" the scan will be. This mainly affects how thick your line work will come out. If you set the "threshold" setting too high the line work will come out thick and chunky and any specks or paste lines in the art will also show up in the scan. Set the "threshold" too low and the line work will be thinner than it is in the original art and you may lose some fine lines in the art. The trick is to know your scanner and software well enough to judge what the threshold should be set on for each individual piece of art. I personally scan black and white line art this way ONLY with art that does not have a lot of detail in it, just basic line art with good solid line work and solid blacks. It works very well for the simple art but if your art has a lot of detailed fine lines such as cross hatching you will probably find that scanning it as line art some of the fine line work gets lost while some fine white areas get filled in. For the detailed black and white line art there is a better way to scan...
Scan as grayscale and convert to bitmap
This is the very best method for getting great scans from detailed line art with lots of thin line work, cross hatching, and detail. It is also a more time consuming process than simply scanning as line art, but well worth the excellent results you will achieve. Here are the steps for scanning line art as grayscale and converting it to bitmap:
1) First off scan the art as grayscale at 600 dpi, scaled to the size it will reproduced at. (Scaling down will reduce the time it takes to scan and process). You could also scan at 1200 dpi grayscale, but over the years I have found that scanning at 600 dpi grayscale gives just as good results as 1200 dpi and scans much faster, so if time is a factor (as it is at my job) 600 dpi works well enough.
2) Once your grayscale scan is complete, the first thing to do is to adjust the levels in Photoshop. Use the Photoshop "levels" to do this, moving the "shadows" slider on the left until the blacks are nice and black, and "highlights" slider on the right until the whites are nice and white.
3) If you scanned your art as 600 dpi instead of 1200 dpi, you would now up-sample your scan to 1200 dpi in Photoshop ( image / image size / 1200 dpi -- make sure the "resample image" box is checked in the "image size window) before you go to the next step. Note: I have found that scanning at 600 dpi and upsampling to 1200 dpi gives nearly identical results to scanning at 1200 dpi.
4) Now that your grayscale scan is nice and clean looking, use Photoshop's "unsharp mask" command to sharpen it up. This is the key ingredient for retaining all the detail in the original art. In the "unsharp mask" dialog box, set the "amount" to 145, the "radius" to 5 pixels, and the "threshold" to 3 levels. I would never use these settings on any other type of scan as they give it a very hefty dose of sharpening, but for a 1200 dpi grayscale scan of line art this will strengthen the weaker lines and also bring out any detailed whites that exist in any cross hatching.
5) Now that your scan has been cleaned and sharpened, use Photoshop's "threshold" command ( image / adjustment / threshold) and set the threshold on 105. A lower threshold makes the lines thinner, a higher threshold makes them thicker. I've found that between 100-110 works best on most line art, the goal being to reproduce the line work as close to the original art as possible.
6) The very last step is to convert your grayscale scan to bitmap. In your Photoshop menu bar go to "Image / mode / bitmap" and the bitmap box will open. Make sure the "output" is set on 1200 pixels/inch and the "method" is set on 50% threshold. Then simply hit "ok" and you will have yourself a beautiful black and white scan. If you find that you still have lost some very fine lines that you want to retain, you can undo the last bitmap command and darken up the lines you lost with the Photoshop "burn" tool, and then convert it to bitmap.
Now you are done! Simply save your scan as a tiff file with LZW compression and your scan is ready for reproduction. If you want to post your scan online, I would convert it back to grayscale, use Photoshop's "image size" to downsample it to 600-800 pixels wide (or however big you want it) and "save as" a gif or jpeg file.
There you have it: the secrets to getting the best possible scans from black and white line art... happy scanning!Author Paul Diamond Blow works as a production artist for a major book publisher with over ten years experience in the field. He is a Photoshop wizard, an Indesign samuri, and a sweetheart of a guy..