Using Photoshop's Levels is a quick way to clean up a black and white drawing or piece of artwork. I use this method a lot for both work and personal projects.
You can work from a scan or a photo of the original. For this tutorial, I'm working from a photo I took. Below is the original hot pizza drawing from my sketchbook.
Open the image or scan in Photoshop and crop out any unnecessary background. Get as tight around the artwork as necessary without clipping in to the line work.
From the Layers panel, add an Adjustment Layer (black and white circle). Select Levels... from the menu. You might need to unlock your Background layer first, do this by dragging the lock to the trash on the Layers panel.
My goal here is to get the background to be completely white and have my lines retain their crisp detail. There are a few ways to make sure the background is #fff, like inspecting with the info panel, but my quick and dirty method is to change the canvas size, Image > Canvas Size... (⌥⌘C on a Mac) to be a little bit larger, revealing the empty canvas below around the edges of the artwork.
Back in the Layers panel, create a new layer and drag it below the artwork.
On the new layer, give it a white fill with the Paint Bucket Tool (G). If white is not your current foreground color, press 'D' then SHIFT+'X'. Now it will be really easy to see the paper change to white. See the corner of the artwork as it currently is:
- Select the Levels Adjustment Layer in the Layers panel again, and using Properties drag the white slider until your paper edges disappear. Change the black and midtone sliders accordingly.
- If additional detail clean up is needed, touchup with the Eraser tool. Don't forget to save.