Correcting a tilted horizon?

[edavies]

As someone new to the digital photography world, I wonder if anyone can help me? Is it possible using PP to correct a tilted horizon? When I say tilted, beginers like me, often find that we concentrate on the composition of a shot - say a landscape by the sea - and remember everything except the fact that the horizon where sea and sky meet is actually not perfectly horizontal. I am presently using GIMP version 2.5 and have access from time to time to Corel Photo Paint 11. Any assistance or advice would be appreciated. Thanks!!

[Dirt_Bike_Ryda]

all you need to do is rotate the photo a little, and then crop it to suit

[kencaleno]

First go to view>show>Grid-(This will show where horizon needs to be)
Then Image>Rotate canvas>Arbitrary
Set an amount-adjust to suit
view>Show.grid-click on grid to remove
Crop image to suit
Regards, Ken

[edavies]

Many thanks for all your comments and advice. I have just tried it and it WORKS!!! I did try it before but found that the horizon seemed have steps in it. I have since discovered the box which says "Anti Aliasing' which keeps the horizon flat after rotating. Thanks again for your advice - much appreciated. - Regards Evan

[PrimeTime]

Originally Posted by edavies

Many thanks for all your comments and advice. I have just tried it and it WORKS!!! I did try it before but found that the horizon seemed have steps in it. I have since discovered the box which says "Anti Aliasing' which keeps the horizon flat after rotating. Thanks again for your advice - much appreciated. - Regards Evan

You can also check for straightness, with gimp, by clicking on the border of the picture and holding. Then drag out a straight edge to check if you rotated properly.

[Japaslavian]

I don't know if GIMP has this or not, but in Photoshop, there is a ruler tool hiding under the eyedropper. You take that and drag it all the way across your tilted horizon.
Then just do Image>Rotate Canvas>Arbitrary, and Photoshop will make the line you just made perfectly straight, thus making your horizon straight as well.
Of course, if the angle is pretty extreme, there will be a lot of cropping to do, and you might lost a lot of information.

[Raigoki]

(sorry for the disruption...)
i do have a question regarding rotating of images.

what i do is i use CTRL+T then pick the edges then rotate....
is there a difference to the Image>Rotate Canvass>Arbitrary
and does it affect the pixels of the image?

[idcrewdawg]

You can use Picasa to do it as well. The function lays the grid, and you use a slider to adjust the image. Really simple in that program.