Extraction

Extractions are the most fun, so we will start with them.


Step 1:
First we need to choose an image to work with.  Since most people see extraction possibilities from everyday photos, we will work with this snapshot of my daughter, Ximina, taken at a market.  For a good extraction some things to look for in a photo include:

  • Contrast between the subject and background - dark hair against a dimly lit background will be difficult to extract.  Ideally, we want a high key shot (white background) or a chroma key background (green or blue screen) that is evenly lit.
  • A pose that will work with the background to be inserted.  Having hands in the image that are holding onto nothing does not work too well.
  • Lighting similar to the background to be inserted.  If the subject is lit from the left and the background lit from the right, it will cause a discontinuity in the image making it look unnatural.

For the background, we will use a scenery snapshot taken at Disneyland.  Some things to look for in a background image:

  • Should be relatively free of clutter and simple.  After all, we did not get the right background when we shot the image which is why we are going through the trouble to change it.
  • Choosing an appropriate background can also make the image quite humorous - see the next page for some examples.

It is important to work with full, unresized, images.  This gives us more room to work with and keeps detail loss to a minimum.

Now that we have the two images we want to work with, lets get started with the extraction.  There are a number of ways to extract a subject.  The most time consuming, but easiest way, is to simply erase around it.  Since we do not have either a high key or a chroma key background, the other extraction methods will not work very well anyways.


Step 2:
We start by opening both images in Photoshop.  Once we have them both loaded, we drag the windows so that they overlap as pictured to the left.  This allows us to move elements from one image to the other.

Select the Move Tool from the toolbar (highlighted on the panel to the left) and click the foreground image, drag it onto the background image and drop it in place.  Move the image around until positioned as desired.

Hint:  I usually press the [Shift] key while dragging so the image is dropped in the center.  We can fine tune the movement after we have extracted the subject and can see the background.

Since both images are layered on top of each other, we no longer need the source window and can therefore close it.

Our Layers Palette should now appear similar to the panel shown on the right.  There will be an eye icon indicating that both layers are visible.  For now, we want to work only with the top layer (the subject) so toggle the background layer visibility off by clicking on the eye icon.

Step 3:

To begin the extraction start out with the Marquee Tool, highlighted on the panel to the left.  On the Tool Preferences Bar (pictured above), select the "Add to selection" icon so that our marquee boxes are added together.  Now we go around and select large portions of the image that we will be deleting to speed up the erasure process. 

Once we have the marching ants as close to the subject as we want, simply press the [Delete] key to remove the masked areas.  The background will now appear as a checker-box pattern.



Step 4:

Now that the bulk of the background is cut out, we need to erase around the edges.  For this we select the Eraser Tool, highlighted on the left panel.  Adjust the brush size by right clicking on the canvas (or [Ctrl] click on the Mac).  Chose a small brush appropriate for the size of the subject we will be working with.

 
We have finished erasing around the subject on the left panel.  On the right panel, we cleaned up the leftovers with a larger brush size, as this does not require as much precision.  We have also gone through and cleaned up the image - we cloned out distracting elements such as the price tag on the hat, and the neck strap to my daughter's camera.


Step 5:

Now it is time to bring in the background.  Simply click on the empty box where the eye icon should be in Layers Palette.  This will turn the background layer visibility on and replace the checker-box pattern with our background image.

Since our subject's position is not where we want it in the final image, select the Move Tool and drag it to its final position.

We can also resize the foreground and/or background so that they match up.  Here we have reduced Ximina so she is a bit smaller.  This way we can crop out the distracting railing from the final image.

 

 


Step 6:

Finally, we want to crop the image.  To do this select the Crop Tool and drag out the area we wish to retain.  The grayed out area represents the section that will be cut out.

Once the crop is complete, we can then make adjustments to each layer individually.  Since we want our subject, Ximina, to be sharp, we sharpen that layer by selecting it and applying the appropriate sharpening.

For the background, we want it to be slightly defocused so that it adds to the image but does not deter focus from our subject.  To do this select "Filter -> Blur -> Gaussian Blur...." and a dialogue box will appear.  Move the slider until we are satisfied with the amount of blur and select "OK."

The background also appeared too bright and the subject a tad dark.  We adjusted black levels on the background to bring down the tonality in the background and made a small boost in the curves to bring up the mid-tones in Ximina.

 

 

 
Done:
All done!  In this final version, I decided to take a bit more of the blankie out from under Nemo.  The end result looks much more interesting than the busy store from where the image was originally captured and has a more natural feel to it.
Of course, we can add any background we want and move the position to wherever we wish.  Here, we positioned Ximina to the left and added a studio backdrop (created in Photoshop) and a bit of vignette to highlight the subject.

 
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