On 01/10/2010 17:36, Frank McCormick wrote:
> Hello all--
>      I have a jpg which I would like to blur the background (focus
> blur I guess) - But I would like the blur to be gradual - when I
> have done this in the past the line between blurred and unblurred is
> too sharp. I have tried the feather selection, but it doesn't seem to
> work very well.  Any suggestions ??
> Thanks

A slightly more manual method using  a filter I wrote, where you can 
select what part of the image remains completely sharp...

1) get and install my WrapMap filter (requires python support) from
http://sourceforge.net/projects/gimp-wrapmap/. I suggest you play with 
it a bit to get acquainted first.

2) duplicate your sharp image (let's call it the 'Sharp" layer) to 
another layer (("Blurred"), and blur it to the maximum blur you want to 
get. Put it on top.

3) add a layer to that image (the "Map", which should as wide as your 
transition area (for performance reasons, avoid being bigger that 200 
pixels). This layer can also be in a separate image...

4)  fill "Map" with  a left to right gradient, black to white.

5) In "Sharp" select the part that should be kept sharp (lasso 
selection, scissors, whatever suits you)

6) That's where is starts being a bit clever: add a layer mask to "Blurred"

7) select the layer mask, fill the selection with black

8) still on the layer mask, apply the Wrap Map filter.  It wil wrap the 
gradient in "Map" around your selection.

9) So now your layer mask has a full black spot corresponding the the 
sharp part of the picture, surrounded by a black to white area which is 
your blur transition

10) Put "Blurred" on top, and make "Map" invisible if it's in the same 
image, and you are done.

11) Using the the various color tools (curves, levels, contrast, 
threshold) on the layer mask, you may alter the linearity of the 
gradient and so adjust how the blur progression happens.

An example is available here; http://dl.free.fr/cnRwtXe8s

PS: If you need a transition significantly wider than 200 pixels, I 
suggest that you prepare the selection/blur map on a scaled down image 
(you can apply WrapMap on a plain layer in this case), then scale up the 
layer to the right dimension, and copy/paste it to the layer mask. If 
you don't know how top copy/paste to a layer mask, it's explained here: 

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