Re: [Gimp-user] Vignetting correction

["phanisvara das" <listmail phanisvara com>]

On Sat, 24 Dec 2011 21:07:22 +0530, Steve Kinney <admin pilobilus net>  
wrote:

> On 12/24/2011 09:30 AM, phanisvara das wrote:
> > On Sat, 24 Dec 2011 19:18:05 +0530,
> > <giuliogiuseppecarlo interfree it> wrote:
> >
> > > Hello everyone,
> > >
> > > i have a problem trying to remove/adding vignetting with Gimp
> > > 2.6.8 and .11.
> > >
> > > I have seen there is a nice tool in Filters-Distorts-Lens
> > > distorsion.
> > >
> > > But if i move only the brighten slider, nothing happens. It works
> > > only if i move also the main slider (and in most images, for
> > > example portraits, i won't need to touch it).
> > >
> > > Is it the intended behaviour or i'm missing something (for
> > > example another tool that only removes vignetting and shows a
> > > preview)?
> > >
> > > Thank you in advance.
> >
> > not sure what type of vignette you're talking about, but to apply
> > one as i used to wile enlarging & developing prints the old way
> > (optically & chemically), i just select an ellipse from upper left
> > to lower right corner, invert the selection, and feather it
> > according to image size. this allows me to either lighten or
> > darken the corner areas, subtly focusing attention on the middle
> > region.
> >
> > if that's the type of vignette you're looking for, i don't think
> > any tool can do that better than the plain ellipse selection tool.
> Hey y'all,
>
> I usually make a new transparent layer, scale it to about 120% of
> canvas size, make an elliptical selection with a high value set in
> "feather edges", invert the selection and and fill it with black.
> Then I adjust the transparency of the layer until I get the effect I
> want - which amounts to a realtime preview of the vignette effect,
> with unlimited do-overs.  If the boundary of the dark area is too
> sharp, use a high value gaussian blur on the vignetting layer.
>
> I make the vignetting layer larger than the canvas because blur
> effects tend to get a little "bent" at the edge of the layer.
>
> There's always more than one way to do things.  For more precise
> control:  Make a duplicate of the main image layer, add a white
> mask, select the area to be emphasized with a feathered elliptical
> selection tool, and fill it with black on the mask.  Then you can
> tweak image component of the masked layer to emphasize the
> "foreground" i.e. the visible part of the original layer - reduce
> brightness and contrast, blur it a little to simulate a flatter
> depth of field on the subject, etc.  If you deliberately "go a
> little too far" with your tweaking on this layer, you can dial back
> its opacity to adjust the amount of distortion in the finished image.

thanks, that's useful. i've never thought much about this vignetting  
stuff. just was something we did routinely with larger prints, because the  
lenses tended to loose light toward the edges.

the way you describe it, it can be used as a creative tool, not just  
subtle final polishing.

--
phani.