Use this tool for corrections to the geometry of the entire document, including its layers. It can be used e.g. for:
- aligning a horizon
- straightening receding lines
- fixing perspective
To make your corrections, either use the sliders in the Side Panel or work right inside the picture by dragging out guidelines alongside the lines to be straightened. A maximum of two horizontal and two vertical lines can be entered. As you add the lines, the program automatically performs the straightening needed, but the lines can be repositioned later at any time. To delete a line, right-click it or press [Delete].
Completely straightened lines can look unnatural; use the Intensity slider, if needed, to soften the correction.
Use the Rotation control to rotate a picture to a precise numerical angle. Beside the slider there is a button for setting the picture’s Horizon [H] – click this button to rotate the picture so that the line you place is horizontal (or vertical, if it is closer to being vertical)
Leave the Crop option active to have the program auto-crop after straightening. The auto-crop is automatically sized so as to cover the largest possible area in the picture possible without adding transparent (empty) areas in the corners. To resize the cropping frame, drag its corners and sides. To reposition it, drag its center. To rotate it, drag outside of it.
Click an item in the Crop Marks list to display crop marks.
Leave on the Delete Cropped Pixels option to remove all image data on all bitmap layers that falls outside the cropping frame. With this option turned off, cropping merely shrinks the document’s border to fit the cropping frame.