create a blur

What method is used to make an image created with a pen blurry, such as a background? Drawings I make are sharp with a pen and I don’t know how to recreate that out of focus look.

What program are you using, or are you talking about a physical pen?

In Photoshop (and probably GIMP) you’d float the foreground on its own layer, then apply a gaussian blur to the background layer.

Motion blurs are a bit trickier. You can use the “wind” filter… it makes a linear blur.

If you want to blur very selectively, you can simply use the blur cursor tool with a very fuzzy brush. That’s useful for glowing bits.

Alternatively, instead of a blur tool you can use a fairly large brush with a low opacity and either hard edge or just barely soft edge and sketch in your background. I find that’s useful for sketching in backgrounds in an illustration, because it’s really just more work to elaborately illustrate a background then lose 80% of the detail when you run a blur filter on it.

There are other ways to get good depth while drawing in pen. Instead of blurry, (like, narrow depth of field), you can also simply lighten the background and foreground and include less detail. That can create some nice effects.

For example…