I recently started to vectorize some old black and white handdrawn designs I created a long time ago. And I ended up with the problem, that some of the scans had a lot of speckles around the lines. One of this drawings was the following “skeleton snake” or whatever you wanna call it:

As I don't have Illustrator, I use Inkscape for tracing the bitmap.

Trying this with the image above will end up in very ugly paths:

As I didn't want to clean the image by hand, I found another solution.

1. Open your scanned drawing in Photoshop.

2. Use “Image >> Adjustment >> Brightness / Contrast…” and increase the Brightness and contrast a bit to remove all the potential noise you have in the white part of the image.

3. Open “Window >> Channels” and Ctrl-Click the RGB Layer to make a selection of the image.

4. Add a mask to you drawing using “Layer >> Layer Mask >> Hide Selection”

Now you can use the “Select >> Refine Mask Feature to refine the Selction and get a smoother look. For me the following settings have worked well. This depends on the size of your image and other factor, have fun playing around with these sliders.

1. Use Ctrl+Click on the refined layer mask to create a selection from the layer mask.

2. Use “Layer >> New Fill Layer >> Solid Color” and choose black as the color.

Save the image and open it in Inkscape. When you now trace the bitmap image using “Path >> Trace Bitmap …” the result will get much smoother without all the speckles.

Here a comparison of the refined bitmap and the results of the vectorication: