Quickguides: scan clean-up for black-and-white linework

When we left off, we had a scanned and merged grayscale, 600 dpi, TIFF image. Right? If that’s not what you have, go back and check the scanning quickguide.

There are many ways to approach cleaning up your image and preparing it for print. The one you choose will have a lot to do with the qualities of the art itself (are you using drybrush? Lots of corrections?), and the destination (are you planning to color? using what method?) Here, we’re going to go over two methods, starting with the most basic approach to prepping straightforward black-and-white linework for print, using the Threshold tool.

Preparing a scan using Threshold

  1. Go to Image > Image Size and size up the image to 1200 dpi. Make sure you do this before any editing.
  2. Save.
  3. If your linework in straight up black and white, with only line-based texture and tone (like stippling and hatching) and not a lot of whiteout corrections and pencil traces, you might be able to save yourself time by just setting the threshold, converting to bitmap, and making corrections.Go to IMAGE > ADJUSTMENTS > THRESHOLD and the following dialogue window will open:
  4. Setting the threshold means deciding where exactly in the spectrum of 256 available grays you want to make your cutoff of black from white. At the default, every gray darker than 128 will go black, and lighter will go white. So slide the little arrow to where your art looks nice and clean. You will see that the higher the number, the darker your art looks. Generally, setting the arrow around 100 to 115 works well for clean black-and- white work. However, if you have used dry brush or inked lightly, or your inking has grayed out a lot from erasing pencils, you may need to use a higher threshold level.If you have very dark, dense art, or lots of grubbiness from over-penciling or using your art as a coaster, you may need to use a lower number. Note that what you’re seeing now is an approximation of what the filter will do, and that the results may vary. You might have to experiment with this a few times before you get it right. Once you have your threshold level just right, click OK to accept it. Zoom in on dense cross-hatching and other problem areas as testing spots.

The instructions above are written for making the threshold adjustment directly on the work. But in many cases we find that using a Level Adjustment Layer to adjusting the threshold is a good course of action. It allows you to revisit your choice of threshold as many times as you need to to get it right. If you want to use an Adjustment Layer, go to the Layers Menu, and click the black-and-white cookie icon on the bottom. Choose Threshold from the options, and adjust your threshold as often as you wish.

You can even select a particular area and apply a different threshold there. When you finish working, though, including making corrections, below, you’ll need to flatten your image before moving on. That will apply the adjustment layer to the work permanently, so remember to Save As…so you preserver your original document with layers intact and you can go back if you need to.

Making corrections

Although you will have already corrected your artwork by hand prior to scanning, Photoshop enables you to make further corrections, such as cleaning up unwanted marks and redrawing lines that may not have scanned well.

Use the MAGNIFYING GLASS tool to zoom in on your art pretty close, but don’t go bananas and zoom to the point where you can’t tell what you’re looking at. Use an orderly pattern to check the art closely for smudges, dots, and schmutz.

Once you’ve located areas to be corrected, use the PENCIL tool, never the BRUSH tool (it has anti-aliasing built in). If you use the ERASER tool, make sure it is set to PENCIL in its options and the ANTI-ALIAS box is unchecked. Alternately, you can use the PENCIL tool only, hitting the X key to toggle the pencil color between white and black as needed to make the corrections.

Tip: Make sure the PENCIL and ERASER are at the same or similar BRUSH size on the OPTIONS. Or you might find it useful to set the ERASER at a slightly smaller size than the PENCIL, since erasing is generally a more delicate operation.

SAVE frequently.

Make the OPTIONS menu for the Pencil tool look something like this.

You can adjust the size of the tool in the Brush box. Here’s the work all cleaned up and corrected:

What is anti-aliasing? On some tools such as the ERASER, the LASSO tool, and the MARQUEE, among others, you have a check box on the OPTIONS menu for that tool labeled ANTI-ALIASED. When you use these tools, make sure this box is unchecked. When you zoom way in, anti-aliased lines look fuzzy at the edges, whereas aliased lines look stair-stepped. At print size, your aliased lines will appear crisper. You’ll also avoid other problems later when you color or otherwise manipulate your scan.

Even if it seems contradictory to you now, trust us, you want stair-stepped, nonsmooth, aliased lines for your final, black, high-resolution linework. We’ve had you make your art so high-resolution that at naked-eye scale, you’ll never see the steps, and the lines will look so much crisper. The first super-sized line—magnified approximately 20x print size—is anti-aliased (looks fuzzy). This second is aliased. This is what you want.



Zoom out and get a look at your artwork. Once you’re completely satisfied with the scan, go into IMAGE > MODE, and convert the art to BITMAP. Make sure that the METHOD in this window says 50% Threshold (meaning it’s set to 128, automatically). Since you’ve already carefully thresholded the artwork, don’t worry. This won’t readjust your threshold level.

Using levels to clean up scans of linework

Sometimes you’ll find that using Threshold is a bit of a blunt instrument. You may have subtle variations in your lines, drybrush, extensive corrections, or other issues that just aren’t getting easily solved with a simple Threshold conversion. That’s when you’ll use Levels, and specifically, a Levels Adjustment Layer, before you Threshold.

  1. Create a Levels Adjustment Layer on the raw scan by clicking on the little half black, half white circle that’s on the bottom of the layer menu and selecting levels. Set your black, white, and gray points by moving the little arrows on the bottom until the image looks right to you. Take note, in particular, of the effect of moving the middle arrow, the graypoint. This is a powerful tool for cleaning up grayish corrections or strengthening drybrush areas. 
  2. Then create a Threshold Adjustment Layer on top of that. Set your threshold, and save.
  3. Linework should always end up at 1200 dpi, though you can work at 600 dpi to make your life easier as long as you haven’t flattened your adjustment layers. But be sure to up-res to 1200 before flattening the document, and save that flat version separately as “final,” keeping the working version with layers intact.

A raw scan with lots of difficult drybrush areas as well as corrections.

A levels adjustment layer beefs up blacks, cleans up whites, and strengthens the gray drybrush areas (black point 21, gray point .83, white point 238, in case you were wondering). A second levels adjust- ment layer was applied to the deep cave only (by selecting that area and creating a new adjustment layer) where we lightened up the gray point in order to save more white in that dark area.
Then, we added a threshold adjustment layer, set a bit dark, at 142. We bumped the resolution up to 1200, and flattened. To see the final panel, after cleaning up with the Pencil/Eraser tools.

Done cleaning up? Upres to 1200 and convert to bitmap

The final step in scanning and manipulating your artwork prior to saving it one last time is to change the MODE to BITMAP. This is the best format from which to print line art.

Zoom out and get a look at your artwork. Once you’re completely satisfied with the scan, go into IMAGE > MODE, and convert the art to BITMAP. Make sure that the METHOD in this window says 50% Threshold (meaning it’s set to 128, automatically). Since you’ve already carefully thresholded the artwork, don’t worry. This won’t readjust your threshold level. You will get a dialogue box that asks you to confirm that you want to flatten layers. Say yes to this.

This tutorial is based on chapter 14 of Drawing Words and Writing Pictures and chapter 9 of Mastering Comics by Jessica Abel and Matt Madden.

Part 1: scanning quickguide