Oops, use the Dodge layer mode instead of screen.  You'll get better 
results.

Brian

On 03/23/2016 11:22 AM, Brian Cluff wrote:
>  > On 03/23/2016 04:49 AM, Michael wrote:
>  > Thanks Brian. I am putty in your hands!
>
> I get the bounces from the PLUG mailing list, so I got your images even
> though they were too big for the queue... nobody else did though, so my
> answer will be the only one based off your image.
>
> Anyway, looking at your pictures, it appears that the darkened edges
> aren't due to fading over time rather they are caused by what appear to
> be a flash going off that lit the center of the image more than the
> edges. This can also be caused of lower quality lenses giving you
> darkened edges in what is called a vignette.
>
> If you want to try and reduce/eliminate it, in gimp you would add a
> layer above your picture, but before you do that, if you have the
> option, go to Image -> Precision and set it to 16 ot 32 bit, so that you
> have more color data to work with.  Unfortunately you'll only have that
> option if you are running the development version of GIMP, but it will
> still work OK if you can't do that setting. Next use the gradient tool,
> changing the gradient type to radial, and make a gradient that goes from
> black in the center fading to white at the corners. (draw the gradient
> from the center to one of the corners).
>
> Then set your new gradient layer's mode to "screen".
>
> At this point the effect will probably be too strong, so you will need
> to play with the opacity till it looks better and you can also play with
> the color curves moving the line on the lower left back and forth across
> the bottom to adjust the shape of the gradient till it better matches
> the vignette in your image.  You can change the gradients layer mode
> back to normal to get an idea of what the color curve adjustment is
> doing to the gradient.
>
> Brian Cluff
>
> On 03/22/2016 06:42 PM, Brian Cluff wrote:
>> Can you send an example so that I can see what you mean by "darkened
>> around the edges"?
>>
>> I'll see if I can easily correct it and then send instructions on what I
>> did.
>>
>> Brian Cluff
>>
>> On 03/22/2016 04:18 PM, Michael wrote:
>>> how does one use a transparent layer? is it only for drawing things on?
>>> I have some old pictures that have darkened around the edges. How I
>>> think I can fix it is to duplicate the layer then  lighten the exposure
>>> value on the lower image, then paint black and uncover the lighter image
>>> over the section that has darkened. How do I do this with gradients and
>>> Darktable?
>>>
>>> --
>>> :-)~MIKE~(-:
>>>
>>>
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