I had a photo that I wanted to blur the background on. I've been using a bunch of different techniques. On this photo, the technique I normally use didn't work that well. So, I started doing some experiments. This is an analysis of the three experiments I tried with screen shots and a conclusion for which work the best. Since there are always 100 ways to do something in Photoshop, feel free to contribute your method of blurring the background if it's different than the three here.

In all three techniques, I started with the following steps:
1) Carefully select the foreground object
2) Save the selection
3) Create a new layer containing just the foreground and put it on top - this will preserve the foreground in it's non-blurred state
4) Create a dup layer of the rest of the image (where we'll do the blurring)
5) Create a gradient mask so only the far away part of the background gets blurred. Note, I'm using elements so I have to simulate a layer mask by grouping two layers together (that's what the adjustment layer with mask is for - it's just a simulated layer mask for the blurred background layer. If I had CS, that would be a little easier, but I get the same affect this way in Elements)

The three techniques I tried where these steps above plus the following:
Method #1: Just blur the whole image under the foreground layer
Method #2: Delete the foreground from the blur layer and delete just the background bits
Method #3: Same as method #2, but lock the transparent pixels in the blur layer before the blur

What I found was that method #1, gave me a halo of color around the foreground that I think was caused by color from the foreground object blurring into the background area as part of the blur operation. I don't know how clearly you can see it in this small web image, but there is clearly a blue halo all along his back in the original.
#1: BLUE HALO:
http://jfriend.smugmug.com/photos/9583616-M.jpg

In method #2, I just deleted the foreground from the blur layer before blurring (trying to avoid the color bleed on the blur). In this case, I got some very weird blur artifact caused by the chain link fence. You can see these artifacts in the blowup above his back, but they exist all along his back. What seems to be happening is that the blur is incomplete around the edge of the deleted foreground causing less blur near the foreground. With some shapes like the links in the chain link fence, this is really obvious and looks terrible.
#2: CHAIN LINK FENCE ARTIFACTS
http://jfriend.smugmug.com/photos/9583618-M.jpg

Finally, I did the same as method #2, but this time locked the transparent pixels before blurring. I knew that this would keep the blur out of the transparent area (which didn't matter to me because that's obscured by the foreground layer above), but I didn't know what it would do to the blur near the edge of the background and whether I'd still have the same problem as in #2. It worked. I got a nice smooth blur of the background.
#3: LOCKED TRANSPARENT PIXELS - IT WORKED
http://jfriend.smugmug.com/photos/9583617-M.jpg

How do others do blurred backgrounds?
--
http://jfriend.smugmug.com
smugmug discount coupon: Bhl3oSIF5zVho