darkening around the edges

[Brian Cluff]

 > 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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