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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> --
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