Turn the background of overlapping shapes transparent using the Pathfinder’s Trim option

07 Jun 2010

A few months ago I received an e-mail from a friend with the question if I could help him out with an Illustrator problem. He created an illustration of a nucleus, based on a group of stacked circles, with a white fill, and a black stroke. He wants to use the illustration in Photoshop, but wants the background of his document shown through…

I want the "fill" area of the circles to be transparent, so the background of my document can show through.
— Dunstan Orchard, designer at Flickr

Illustration based on Dunstan Orchard's nucleus drawing.

First thing that came to my mind was that one of the Pathfinder options would be the obvious answer. The only question for me was "which option of the Pathfinder do I need?". You see, I totally love the power of the Pathfinder, but for some reason, there are a few in there that keeps me stumped what their function is. The ones that confuse me are in the second row. They are the destructive ones: Divide, Trim and Merge.

What I want as a result, is turn the black strokes into fills, and the white areas of the shape into transparent gaps. So how do we get rid of all the overlapping paths of the circles, without destroying the original shape of the nucleus, and have all the black lines still in tact? Here is how…

nucleus consisting of stacking circles, using the Pathfinder's Trim option
  1. Our starting illustration consists of shapes (in our example, circles) in stacking order.
  2. Select the whole shape and choose the Trim option from the Pathfinder (2nd row)
remove the fill and add back the stroke, then turn the stroke into a fill
  1. Now the paths are linked like we want them to, but the stroke is gone. Remove the white fill, and give the shape back its black stroke.
  2. Turn the stroke into a fill: go to Object > Path > Outline Stroke

Now you have a perfect shape you can copy and paste into Photoshop as a Shape Layer and play with it. Let the background show through, or use the shape as a mask like I did in my example. Shape Layers are great to work with in Photoshop as you keep things resizable and flexible. I always try to use them where I can.

The Live Paint method

Like with many things, there are multiple ways to achieve the same result. This other method with the Live Paint feature is a hat tip by oVan:

  1. Select the whole shape and choose Object > Live Paint > Make
  2. With the object selected, give it a transparent fill
  3. Go to Object > Live Paint > Expand
  4. Go to Object > Path > Outline Stroke

Comments

  1. 1 Chris 07 Jun 2010

    Awesome!  Thanks for this.  :)

  2. 2 Simeon 07 Jun 2010

    Awesome article. I’ve wondered for the longest time how to do this, not sure why I never experimented more with those Pathfinder buttons I never use.

    This is a function that is common in Sign Writer’s applications but I’ve thought was missing in Illustrator. Turns out, it ain’t!

  3. 3 Mordy Golding 07 Jun 2010

    Nice example, Veerle!

    Ever since Live Paint was introduced in CS2, I’ve said that “Pathfinder is dead to me”. Pathfinder is just old school, especially now with the Shape Builder tool in CS5. Also, there’s no need to expand the Live Paint group in your steps above—you can copy and paste it right into PS if needed (Illustrator handles any necessary expanding on the way). Of course, you can also use the art as a mask right in AI as well.

  4. 4 Veerle Pieters 07 Jun 2010

    @Mordy Golding Thanks for the tip and info. It sure looks like I should use Live Paint more as I ‘almost never’ do. I actually kinda forgot about it :-/ I’m so used to the Pathfinder for ‘jobs’ like this. As far as the Shape Builder in CS5, it sounds interesting but I’m still with CS4 at the moment. I haven’t upgraded yet. So if you skip the expanding, I assume you paste it as a Smart Object in Photoshop then, right? I just tried it as a Shape Layer, but that doesn’t work (bad result).

  5. 5 Jos 07 Jun 2010

    interesting! I haven’t seen that before. Good timing to practice :)

  6. 6 Mordy Golding 08 Jun 2010

    @Veerle Pieters When you paste it as a Shape Layer, it doesn’t look correct because the artwork is stroked in Illustrator and shape layers can’t have strokes (actually the concept of strokes doesn’t really exist in PS at all). In this case, a Smart Object is the best way to go—because it appears correct in AI, it’s scalable in PS, and if you need to edit it for any reason, you can edit the smart object back in Illustrator—where the art is still a fully-editable Live Paint group.

  7. 7 John Mindiola III 09 Jun 2010

    Shape builder? Ugh. It won’t kill off Pathfinder, it’s just for those who never understood it in the first place, which is sad. Live Paint has its time and place, but Pathfinder is still the most robust way to edit shapes of all sorts.

  8. 8 Bogdan 21 Jun 2010

    Great work, thanks for sharing! :)

  9. 9 Jeremy Darko 28 Jun 2010

    That was great! Thanks for sharing!

  10. 10 bizee1 30 Jun 2010

    Thanks for this tut, its one Ive never seen before and is very helpful..much appreciated!

      bizee1

  11. 11 Bartosz Oczujda 08 Jul 2010

    Short and to the point, my favourite type of tutorial.

    And I choose the pathfinder method. I guess I’m oldschool ;-)

  12. 12 Oscar 15 Jul 2010

    Wow! Going to try this when I get home. Very, Very nice!

    I like your website!