On Wed, Sep 16, 2009 at 7:02 AM, Bob Meetin <b...@dottedi.biz> wrote:
> Subject says it all.  I have a large assortment of product pictures
> which I need to give uniform backgrounds, preferably white.  Can someone
> point me to a tutorial that discusses how?  You can see a representative
> sample image at: http://www.dottedi.biz/images/diagnostics/DSC_4355.JPG.
> They can probably live with the shadows if I can lose the bulk of the
> background.
>
> Thx, Bob

For this kind of thing, there is the name 'greenscreening', in which a
matte, contrasting color is used as a background for an object,
allowing the object to be easily separated from the background.

In that case, Foreground-select is ideal.
However, you basically have the opposite: A photo of a bluish-gray
object on a bluish-gray background. Naturally this is very hard to
separate automatically!
So for such pathological cases, paths is probably a better choice.

Smoothness is not a big deal (in fact the selection created by
foreground-select is entirely binary, no smoothing involved)... this
is because you can convert the selection to path and then that path
back to selection if you want it smoother.

If I needed to handle your example in the way you want, I would:
* use foreground-select to get a rough approximation (make sure that
there are no 'holes' by marking areas as foreground as needed)
* enter QuickMask mode (click the icon to the left of the scrollbar)
* select paintbrush with an appropriate brush and black color, paint
away the wrongly selected parts
* exit QuickMask mode (click the icon to the left of the scrollbar)
* Select->To Path
* Tweak the path if needed
* right click on the path in the Paths dialog -> 'Path to Selection'

If your example wasn't pathological (ie if it had a good contrasting
background), I would just use foreground select, convert to a path,
tweak the path, and convert it back to a selection.

Afterwards in either case, I'd probably just Select->Invert and fill
with white (like this: http://i26.tinypic.com/bdpjm0.jpg )
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