I think I'll spend a day (week?) reading the Linuxtopia book.
On Wed, Mar 23, 2016 at 4:13 PM, Brian Cluff <
brian@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@snaptek.com
>> <mailto:brian@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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