Just keep in mind that the book on linuxtopia, grokking the gimp, is 16 years old. I'm sure there are plenty of good examples, but the gimp has changed significantly since then, so you might have to do a little searching for features that have moved.
Brian CluffOn March 23, 2016 7:12:40 PM MST, Michael <bmike1@gmail.com> wrote: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:PLUG-discuss@lists.phxlinux.org><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?
--
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