The Parallax Experiment

Given that the current hot topic in home videography is “home 3-D movies” (both camcorders and screens to view them) I thought it would be appropriate to attempt making some 3-D on the “cheap.”  Really cheap.

I got the idea from Ashton Kutcher – actually, a video he posted in the Nikon Festival contest.  If you look closely at the stills in his video, you’ll see what’s known as the “parallax effect.”  In other words, an object in the foreground moves in relation to the background – simulating the changing position of the viewer / camera, and adding a bit of a 3-D effect.  The idea is that if you move your vantage point from right to left, objects nearer to you will shift to the right more quickly than distant objects.  Apparently it’s useful in astronomy, as in when you’re measuring distances between stars and galaxies.

I wanted to take a collection of stills I had turned into a slideshow some time ago and see if I could create a parallax effect without having the equipment – and staff – Ashton Kutcher likely has available to him.  And here is what I ended up with:


while you were sleeping… from Tom on Vimeo.

As you can see I did not apply the effect to every still.  Sometimes it works, sometimes it doesn’t.  And sometimes it seems like it should work, but due to operator error (failure to accurately imagine how moving a virtual camera will affect the scene) makes the whole effect kind of cheesy.

But here’s the basic idea.  You take a photo that has clearly defined foreground objects, maybe also some mid-range objects, and some far-off background.  If it’s difficult to cut out, like bare tree branches, skip it.  Ditto if there is a sunburst effect that overlaps your foreground objects – it’s too hard to separate.  These silhouettes in the video I did seem to work pretty well.

Using photoshop or photoshop elements, use your magic lasso to “cut out” the foreground objects.  Create a new layer from your clipboard, and save it as a GIF file.  You’ll lose some color detail by doing this, but as far as I know it’s the only way to allow transparency – which you’ll need in order to see the background.

Now go back to the background and delete what you just cut out.  You’ll notice you have some dips and jags where there is white space.  You’ll need to fill these in somewhat, because when you move your perfectly fitting foreground in relation to the background, these gaps will show up.  So use the clone stamp tool – again, using a sky background makes this easier – and use similarly colored sky areas to gradually close up your gaps as well as you can.  Basically you’re looking for an overlap between your foreground and background so you can move things around without opening up white space.

Now you go to your video editor.  The background photo will be your first timeline.  Now import your foreground photo(s) and put them in the second, third timeline(s) as appropriate.  The first thing you’ll need to do is adjust sizes so that the original photo has been recreated.  You may want to fudge a little and make your foreground a little bigger – say 105% – to give you more wiggle room.

Now you need to animate the clips.  You have to decide how your camera is going to move.  Left to right?  Simultaneously zooming?  You may want to focus on a particular feature of your photo, as if the camera is moving forward alongside that object.  And you may want to draw a diagram for yourself.  But as a simple example, if you move your camera from right to left, everything in your scene will move left to right.  So you’ll want to give yourself room to do that by increasing the size of your photos and letting a little hang out the left side of the frame.  If using premiere or premiere elements, you then adjust your “x” coordinate at the beginning and end of the clip (using edit effects and clicking on the little clock icon on the appropriate effect).  You want objects close to you to move more than objects farther back.  So a bush may move 25 pixels left to right, and the sky in the background may only move 5 pixels.  Then you have to check and recheck to make sure (a) it looks natural and (b) there are no gaps created during the movement.

To get the hang of this, you’ll need to experiment.  The clip above was my first attempt, and let’s just say it took WAY too much time to create what you see.  Try adding zooms along with your pans and the issue becomes much more complicated.  But I think it’s a cool effect, and well worth learning, if only it helps you understand how parallax works in order to assist you in framing future shots and projects.  Good luck!

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2 Responses to The Parallax Experiment

  1. Yoshi says:

    Nice! Just what I was looking for. I had the impression that it was some easy job with some programs, but I guess you gotta do it manually. No problem though, I will give it a go. Anyways, thanks for the tut!


  2. admin says:

    It might be there is some program that will do it – I always like to try it manually so I understand how it’s supposed to work. If you hear of one, I’m all ears!

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