7.6. Transform

The Transform submenu of the Layer menu

The Transform submenu of the Layers menu contains operations that flip or rotate the active layer of the image.

Flip Horizontally [or Vertically]

These commands can be accessed from an image menubar as Layer->Transform, followed by Flip Horizontally or Flip Vertically

"Flip Horizontally" reverses the layer left-to-right, and "Flip Vertically" reverses it top-to-bottom. Both commands leave the layer dimensions unchanged; neither causes any degradation of pixel data in the layer.

Rotate 90 degrees CW [or CCW, or 180 degrees]

These commands can be accessed from an image menubar as Layer->Transform, followed by Rotate 90 degrees CW, Rotate 90 degrees CCW, or Rotate 180 degrees.

Each of them rotates the layer in the specified way, with no degradation of pixel data. The shape of the layer is not altered: note that this may cause it to extend beyond the bounds of the image. (In GIMP this is permitted, and does not force the layer to be cropped. You will not, however, be able to see the parts that extend outside the image unless you resize the image canvas or move the layer.) The center of the layer will be located at the same place after rotation as it was before rotation.

Arbitrary Rotation

This command, accessed from an image menubar as Layer->Transform->Arbitrary Rotation, it is an alternative way of activating the Rotate tool.

Offset

The "Offset" dialog

This command can be accessed from an image menubar as Layer->Transform->Offset.

"Offset" allows you to shift the contents of the active layer; it does not change the dimensions of the layer. Anything that gets shifted outside the edges of the layer is cropped away. Choosing this menu entry brings up a dialog that allows you to specify how the shift should be performed. You can set the distance to shift the layer in the X and Y directions, measuring from the upper left corner, with positive numbers representing movement to the right (X) or downward (Y). The default units are pixels, but you can use the Units menu in the Offset area to change this if you like: units of "%" are sometimes useful. Pressing the button labeled "Offset by x/2, y/2" will cause the layer contents to be shifted exactly half the width and height of the layer. There are three possible ways to treat the areas left empty by the shift, specified by "Edge Behavior":

  • Wrap around.  This option causes the empty space to be filled with the parts of the layer that are shifted outside the edges.

  • Fill with background color.  This option causes the empty space to be filled with the Background color shown in the Color Area of the Toolbox.

  • Make transparent.  This option causes the empty area to be made transparent. If the layer lacks an alpha channel, "Make transparent" will not be available.