The Rotate Tool Options
GIMP’s Rotate tool offers many options that are similar to those of other image editing apps such as Photoshop.
Transform
By default, the Rotate tool operates upon the active layer; look to the right of Transform to see where to change this option to Selection or Path. Before using the Rotate tool, check the Layers or Paths palette to make sure the layer, selection, or path you want to rotate is the active one. When rotating a selection, the selection will be obvious on the screen because of the selection’s outline. If Transform is set to Layer, only the part of the active layer within the selection will be rotated.
Direction
The default direction setting is Normal (Forward); applying the Rotate tool turns the layer in the direction you’ve specified. The other option is Corrective (Backward). At first glance, this seems to make little practical sense. However, this is an incredibly useful setting when you need to adjust horizontal or vertical lines in a photo, such as to straighten a horizon where the camera wasn’t held straight. To use the Corrective setting, select View > Show Grid (or, select Guides in the Rotate options and choose whatever option is most helpful, as shown later in this tutorial). Click on the layer with the Rotate tool, and rotate the grid until the horizontal lines of the grid are parallel with the horizon.
Interpolation
There are five Interpolation options for the GIMP Rotate tool. These affect the quality of the rotated image.
Cubic (the default) generally offers the highest quality and is usually the best option.On computers with less processing power, the None option helps speed up the rotation if the other options are unacceptably slow; however, edges may appear jagged.Linear offers a reasonable balance between speed and quality on less powerful machines.NoHalo and LoHalo help remove halos, the artifacts that can appear around elements in images when they’re altered. Experiment with these to find what works best for any particular image.
Clipping
This becomes relevant only if parts of the element being rotated will fall outside of the existing borders of the image.
When this option is set to Adjust, the parts of the layer outside of the image borders will not be visible but will continue to exist. So, if you move the layer, parts of the layer outside the image border can be moved back within the image and become visible.When set to Clip, the layer is cropped to the image border; if you move the layer, there will be no areas outside of the image that will become visible.Crop to result and Crop with aspect crop the layer after rotation, so that all corners are right angles, and the edges of the layer are horizontal or vertical.Crop with aspect differs in that the resulting layer’s proportions will match the layer before the rotation.
Guides
The Guides option lets you select the type of guides you’d like displayed on the image to help you make your adjustments. The choices include:
No guidesCenter linesRule of thirdsRule of fifthsGolden sectionsDiagonal linesNumber of linesLine spacing
Choose whichever setting is most helpful for the adjustments you’re performing.
