darkening around the edges

Michael bmike1 at gmail.com
Wed Mar 23 19:12:40 MST 2016


I think I'll spend a day (week?) reading the Linuxtopia book.

On Wed, Mar 23, 2016 at 4:13 PM, Brian Cluff <brian at snaptek.com> wrote:

> Here's some specifics of the blend modes.
> https://en.wikipedia.org/wiki/Blend_modes
>
> http://www.linuxtopia.org/online_books/graphics_tools/gimp_advanced_guide/gimp_guide_node55_002.html
>
> For your example pictures, screen will over brighten the darker areas of
> your picture, so dodge produces a better result.  In a different picture,
> screen could be the better choice.
>
> Brian
>
> On 03/23/2016 12:56 PM, Michael wrote:
>
>> please, what is the difference between the two modes?
>>
>> On Wed, Mar 23, 2016 at 2:35 PM, Brian Cluff <brian at snaptek.com
>> <mailto: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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-- 
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