Photoshop answers reader's questions in this tutorial how-to use Photoshop Actions to remove backgrounds from 36 digital photos in the Photoshop Tips & Tricks Department of the Design & Publishing Center

Setting the Stage for Photoshop Actions

The Question: 36 Backgrounds to remove
I am doing a project to make 3D photo which is basically a series of photos (36) of an object taken from different angle( every 10 degree). Most of the time is spent in extracting the object from the background since there are 36 photos for each object. Is it possible if I took a blank photo of the background and use it to subtract all the other 36 photos with just a few click? Or is there a better way to do this?
The Answer: Photoshop Actionsthe shot
WOW... what a great project. We'd like to see some screen shots and before/after of this project for an article in Photoshop Tips & Tricks!
We've given some thought to this problem, and seem to keep getting back to the same conclusions you did.
Set it up right the first time
We saw a Photoshop Action would be just the right thing, but it would work even better and easier if the shot was staged first.
      If you're setting up to shoot an object many times -- and the background must be removed, then get a good shot of the background with NO subject. This sets a uniform, unchanging background to show off the object. If the object sequence is for a movie or QuickTime VR, or even an animated GIF file, then this set-up is a must.
      Bring in a neutral gray or off-white backdrop cloth, paper or screen, to shoot the rotating subject. This makes a background that can easily be extracted with the Magic wand.
      Stiff background paper is probably the best because it won't develop wrinkles to deal with.
      Make sure the color CONTRASTS with your subject. If the subject has 20% or more color difference from the background paper, this should be enough. I've been known to light the backdrop separately too, but that's another story.
      Be careful not to get a background too close to the color values of the object. I would have perhaps gotten a medium blue background paper since there are no blues in the sculpture. This will allow me to crank up the tolerance of the wand until a perfectly clean selection later when we go to process the files.
      Now light the setting as evenly as possible to avoid unsightly shadows, make sure the background doesn't change -- keep the camera steady on a tripod, always located in the exact same spot, and fire away.
      John's in good shape here because he's using a turntable which allows him to rotate the object with very little effort. He can also mark the turntable so he moves the object the same amount each time.
In this diagram, we give you an idea of how the setup provides ideal shooting conditions.
Processing the Sequence
Once you've shot all the iterations, then it's time to bulk process them.
      The first step is to make a first test -- running through the technique until the steps are perfect. This will take a few minutes.
      Begin by testing with the magic wand, adjusting the tolerance in a trial and error fashion until the Magic Wand selects only a clean, continuous selection line around the background.
      If the object is particularly sculpted, and shaped, perhaps the EXTRACT filter might be faster. See our tutorial on using the Extract filter. However the Extract filter will be all but impossible to script into an action.
      With that accomplished, make the changes to the background necessary to knock the object out.
  1. Always work on a copy of the image, or a dupe of the image layer.
  2. If you are lightening only, then use Image > Adjust > Brightness/Contrast, or the Levels dialog.
  3. If you plan to delete completely, then set a one or two pixel feather then delete.
After each operation check to make sure it's going to work to your satisfaction. If not, back up and try again, changing the parameters. Keep concise notes of HOW the correct settings are achieved -- each step. You'll want to remember the steps you took for the next step.
Building a Background Action
  1. Open "Actions" palette
  2. Click "New" button, and Name your action
  3. Click the "Red" button at the bottom and "Record"
  4. Carefully walk through the steps required to achieve the "Correct" knockout
  5. When complete, Click the "Stop" button (Black Square)
Congratulations, you've now created an "Action" to knock the background out. Select File > Revert and forget the changes you made, or close the file without saving, and open another.
      Now, click the "Play" button in the Actions Palette. (Right pointed arrow) Observe the results. If they are correct, you're done. If they are not correct, then back-track, and check to make sure each step is exactly the way it needs to be, then record again.
      It may take several tries, but once you're finished you'll have an automated color correction for all such "bluish" scans.
Tips for Building Actions
When you click with the magic wand, be careful to click where you know it's okay to click in each file. If the series of steps is too complicated, then break it up into multiple, logical sequences. You won't be able to "batch" process, but you'll be able to quickly select and play the second sequence. If you get it absolutely perfect, then you can "Batch" process the whole folder by using the File > Automate > Batch command.
And that's about all there is to it!
From Photoshop 911 Case #10/06/2003
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