I’m a long time GIMP user (15+ years) but I can’t find what I would think is a basic function. I would like to rotate my image enough to get my vertical lines straight up and down. I can use Guides in the Rotation tool, but those rotate along with the image. RawTherapee has this feature under Lens/Distortion, but I’m not finding anything similar in GIMP. Suggestions?
How about dragging a ruler
to a suitable position and then
rotate against that?
Claes in Lund, Sweden
Good call. Thank you.
I remember this from the very first episode of ‘MeetTheGimp’, many years ago. I think it might even have been Gimp 2.6
However, use the rotate tool in Corrective Mode, rotate the grid to match a vertical and apply. These days the same method, using the unified transform tool, especially if you need to apply any perspective correction as well as rotate.
For a plain rotate, use the measure tool, draw down a known vertical, apply.
Thank you! That’s a great method to know.
The measure tool offers as straighten option if that is all you are wanting to do. Really easy to use.
Old Gimp: This is the “Corrective” move of the rotate tool. In that mode the guides rotate, so you align them with your verticals/horizontals, and when you apply the rotation the lines that were parallel to the guides become vertical/horizontal. This method also works with other transform tools, in particular with the Perspective one.
Since 2.10.something: this can also be done with the Measure tool. Measure the angle or a vertical or the horizon, and then hit the “Straighten” button in the Tool options.