dinasset,

Thank you for the quick reply.
I have learnt something new! In future I will use your method on subjects where distortion will not show, because it gives more control of how much of the image I will lose by cropping (if any).
I will use my original method (Transform/Rotate) where the subject has a regular grid structure which will show distortion.

david.

I have often perspective problems, that's the reason why I'm using frequently Perspective, but only to adjust the horizon your method is the appropriate one

Thanks Everyone ... I'm learning how to use Gimp.
Had to try the Perspective tool .. it worked great.
So, this is with the Perspective Tool and cropped.
I used:
Colors>Auto>White Balance
Then a Luminosity Mask on D
Adjusted Curves
Back to Colors>Auto>Equalize and set to 55% Opacity
G'MIC > Tone Enhance

I'm happy to learn so many new things here in the thread about enhancement. My tries where I have applied horizontality as Dinasset said. I corrected colour balance and contrast too, Layer masks to correct only parts of the pictures. Thanks to you all
I leave these pictures and my tries.

My tries

Like your results Issabella !
Only time for one, then back to real world.
Good ole G'MIC
Duplicate image
Top Image,
G'MIC>Basic Adjustments>Brightness +6%, Gamma +28%,Saturation +12%
G'MIC>Boost Chromatically
Lower top layer opacity to 85%

My attempts at the latest two photographs.

1st. (011): rotate 2.79 degrees, heal transparency, duplicate, Luminosity Mask LL, Blue to 120%.
Bottom layer, increase Green & Red and slight decrease of Blue to increase contrast with sky and water.
Cropped foreground to lower horizon. The intention was to make the sky and water a greater part of the picture to increase the feeling of space and distance.
Scaled to 2000 x 1200 and sharpened.

2nd. (002): Scaled to 2000 x 1500 and then cropped 200 px from the foreground, again to emphasise sky and distance.
Duplicated. Luminosity Mask LLL, Blue to 120%.
Duplicate base image. Mask MM, darkened slightly using curves (trying to make distant mountains more obvious).
Duplicate base image. Mask DDD, darkened foreground bushes and trees to silhouette,
Flatten image and sharpened.

david.

I like your results a lot. They are good,
Tom and David each result in different style and I like them a lot.
I did another try on this picture and my steps were: Gmic - Colours - Colour Balance- After that Gmic - Colours - Boost Chromaticity 0.30. Tone mapping and wavelet sharpening.
A question; when predominate a colour (for instance green colour in the first picture) how does one low the intensity?

Issabella,
I can suggest several ways of changing the intensity of a colour.
1. You can use Colours/Curves and adjust the individual curves in different brightness regions - this is what I did with the first one. (I actually increased Red and Green in the darker areas and decreased Blue)
2. You can use Colours/Components/Channel Mixer. If you decrease, for instance Green in the Green Channel you must increase Red and Blue so that the total of the three percentages is 100%. If not, you will have a colour cast.
Two screen-shots to explain:

3. As I have done in my re-try of this picture!
I chose a Luminosity mask which was Black for the trees and then painted the grass area with black. Then I was able to adjust the sky, water and distant hills on the top layer and darken the trees and grass on the bottom layer.

I hope this helps.

david.

You can use the "Clop to result" clipping setting of the Rotate tool (and other tools) to clip to the largest rectangle that
fits.

Be very cautious with the Perspective tool. It obviously doesn't preserve the aspect ratio of things, and I'm not even convinced it does the proper thing to fix the perspective in architecture shots (the perspective tools in some other photography software may give better results).

Personally, when doing architecture shots, I use a wide angle lens and shoot horizontally when I can. Of course half the picture is the ground, but the resulting picture, even with half the pixels, will be sharper than the full picture after a perspective transform.

An even more extreme interpretation of one of the photographs.
Numerous layer masks to isolate different parts of the image and many "tweaks"!

david.

Thank you so much David. Your answer helps a lot for me. I wanted to know how you really adjust it and which way was the best to act.
I'm happy I am improving my results little by little thanks to you all.

Tonemapping and colors:

Issabella, you can play with G'MIC filter "Specific saturation". With opposing and input, you can do a lot, if there is a predominating color. Also play with GIMP color balance and curves (GIMP or G'MIC).

Only the methods described above:

Of course you can also try to reduce saturation first in GIMP Colours> Hue-Saturation.

Thank you so much iarga. Good methods. I've been practising them just now and they work great, too.

Issabella, do you know this tutorials by Pat David?

Basic color curves
Getting around in gimp color correction
Color curves matching

They are very useful too.

Two more pictures for anyone to improve.
Back to Greece again! Cruise ships in Argostoli harbour and, since we have had the old Sissia Monastery, now we have the new!

david.

Thank you so much iarga for the tutorials. All of them are very interesting and I'm practising that information.
David, two beautiful pictures I hope not to spoil