Deke's Techniques 022: Removing People with Image Stacks

Today's Deke's Techniques explains how to magically remove unwanted people from a photograph. Crazy as it may sound, you can take anything that moves in a scene---a person, a car, or even a distended orangutan head---and make it disappear into thin air. Suddenly a crowded plaza or distant vista becomes altogether vacant.

This technique requires two things: First, you'll need to shoot several exposures of the scene so that Photoshop can compare the stuff that moves to the stuff that doesn't. And second, you'll need Photoshop Extended. Either CS3, CS4, or CS5 will do just fine; but you have to own the Extended version of the software to pull this technique off.

Assuming you have both of these, the tool of choice is the image stack. Like a super-powered blend mode, an image stack takes a smart object-full of images and runs a kind of statistical analysis on every pixel across multiple images. Which is to say, it blends the similar pixels one way and the different ones another. So an image stack either wipes out or highlights differences.

Here's the official description from lynda.com:

Have you ever wanted to capture a pristine photo of a famous location that was unmarred by the presence of other people or random objects? Imagine the Golden Gate Bridge with no cars or the Piazza San Marco with no tourists. While you're not likely to ever have those locations all to yourself, this week's Deke's Techniques shows you how to simulate that kind of exclusive access using the image stacking capabilities of Photoshop CS5 Extended. In this free video, Deke McClelland shows you how he removed a pesky tourist from his shots of a famous theater by aligning multiple shots, turning all those layers into a single smart object, and then applying a Median calculation to remove his fellow traveler (not to mention an inexplicable floating monkey head) from the scene.

In Deke's case, this pesky woman was walking along the railing at the Teatro Olimpico in Vincenza, Italy, while he was trying to capture Palladio's amazing forced-perspective set. (Below, he actually used an alternate image stack, Minimum, to show you all four of her positions at once!)

What is this person doing in my scene?!

Then, without having to rely on a single mask, Deke managed to remove her by simply asking Photoshop to do the math. And he ends up with this altogether unfettered result:

Thanks to the Median image stack, now she's gone

During the course of the video, you'll also learn some of the other calcuations that Photoshop Extended offers. And you'll see how to troubleshoot remnant artifacts if your calculations don't do the job satisfactorily.

Every week, Deke offers up another handy free technique for you to use in your own projects. As if that's not enough, lynda.com members can access exclusive videos from Deke as well. In fact, this week, he'll show you how he turned a crowd in Piazza San Marco into a compelling set of ghostlike figures. Try it out and see what kind of serious power it gives you over your photographic surroundings!

And join us next week for another free technique from Deke. Ciao, fellow Photoshop travelers!

As hinted above, members of the lynda.com Online Training Library can look forward to a follow-up video in which I demonstrate a creative application about image stacks. This time, we take three lightly populated photos of Saint Mark's Square, including the one below:

One sample Saint Mark's Square photograph

And turn all moving objects---most obviously, the people---into apparitions. Even the moving cruise ship in the distance shines like a ghost vessel.

Three photos of Saint Mark's Square merged to produce ghosts

Next week, I'll show you how to create synthetic wood grain. In the meantime, keep an eye out for ghostly Photoshop things. Or learn how to make them for yourself. The choice is yours.

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Comments

Amazing tutorial. One small

Amazing tutorial.

One small comment about this technique: you need at least THREE images to make this work. In case of two-image stack, median mode is equivalent to mean, which give you the averaged-ghost image (not what we want in this case).

This is really a nice and

This is really a nice and informative, containing all information and also has a great impact on the new technology. Thanks for sharing it
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Excellent point

Someone knows their statistics!

Thank you

Many thanks for another awesome tutorial, not seen this demonstrated before.

Bit of a Photoshop nut.
http://www.tipsquirrel.com/