darkening around the edges

[Michael]

please, what is the difference between the two modes?

On Wed, Mar 23, 2016 at 2:35 PM, Brian Cluff <brian at snaptek.com> wrote:

> 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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-- 
:-)~MIKE~(-:
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