SL shots lack so called "depth of field". In RL you focus on something and the elements in front of your focus point and behind it become increasingly unsharp as they are further from the focus point. How blurry they become depends on a number of factors that are not really important here like the focal lenght of your lens, the aperture etc. What does matter is that applying some blur to the background of your pictures brings out your main object and feels more real.
Making a decent blurred background can be a tedious job if you do it the traditional way as explained very well in Vint Falken's tutorial by making a mask. Not anymore...
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The rest of the story is Photoshop editing. Open both bitmaps in Photoshop. Use control-a to select the whole "depth" picture and and control-c copy it. Now go to the actual colored picture. If you're lucky enough to have CS3 duplicate your background layer* and convert the copy to a smart object (right click the layer for the menu). In the layer thumbnail you should now see the smart object icon. From the filter menu select blur > Gaussian blur and apply a generous dose. In your layer appears a smart filter thumbnail.
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If you don't have access to CS3 you can do it another way. Again open both the color version and the depth version of your picture. Start by inverting the depth picture by hitting control-i (or go to the top menu image > adjustments > invert). Select and copy the inverted depth picture as before. Select the color version and make two copies of the background layer. Of the three layers you have now select the middle one and apply some degree of Gaussian blur to it.
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However, there are some drawbacks. The "depth" picture doesn't pick up on transparent objects so they take on the blur of what's behind them and there is the fact it doesn't account for foreground blur. On top of that the grey areas in the mask are actually partially transparent so the sharp smart object or underlying layer is showing through to some degree which gives those areas a somewhat haloed look. Nevertheless I'm sure it can serve its purpose as a quick way of enhancing a picture.
as an example:
This one...
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... plus this one ...
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... makes this one :-)
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I would love to hear your comments and suggestions on refining this technique and I'd love to see your pictures created using it.
On a side note: sorry for the somewhat messy layout of this post, the template was not intended for tutorials :-)
* I like to keep the original background layer untouched so I can always go back.