Shortcut

The Shift-p key combination will change the active tool to Perspective.

Overview

The available tool options for the Perspective Tool can be accessed by double clicking the Perspective Tool icon.

Affect

Affect icons let you choose the element, current layer, selection or path, the tool will transform:

• The Transform layer lets you modify the perspective of the selection content (the whole layer if there is no selection.

• The Transform selection lets you modify the perspective of the selection boundaries.

• The Transform path lets you modify the perspective of the current path.

	Warning
	Remember that your Affect choice persists after quitting the tool.

Transform Direction

Forward (Traditional): Performs transformation according to the direction of grid lines: if grid is bent 10° to the left then the image will be bent 10° to the left too.

Backward (Corrective): Performs transformation in the reverse direction of grid lines: if grid is bent 10° to the left then the image will be bent 10° to the right and so will be set upright. This option is used to correct perspective deformations. You bend grid lines to align them on the image lines that you want straighten up then you click Transform in the Info Window. You can have to clip the image after this transformation.

Interpolation

The Interpolation drop-down list allows you to choose the quality of the transformation. For more information about the different methods that can be employed, see the glossary entry Interpolation.

Clip Result

This option will clip the transformated image to the original image size.

Preview

Here, Preview is superimposed on the image. The drop-down list gives you four possibilities:

1. Outline: Puts a frame to mark the image outline, with a handle on each corner. Movements will affect this frame only on the Preview, but the result of the transformation will concern either the content or the boundaries of the selection according to the selected Affect mode.

2. Grid: Puts a grid on the image, with four handles. Movements will affect this grid only on the Preview, but the result of the transformation will concern either the content or the boundaries of the selection according to the selected Affect mode.

3. Image: Here, the preview is a copy of the image superimposed on the image, with an outline. Movements affect this copy and the underlying image appears.

4. Grid+Image: Both turn at the same time.

Preview type is only for greater convenience. Whatever your choice, result will be the same when you clic on the Transform button in the Perspective Transform Information dialog

Options with grid activate a drop-list with two options: Number of Grid Lines will allow control over the total number of displayed grid lines. Use the slider to set the number of grid lines. Grid Line Spacing allows control over the distance between the grid lines. Use the slider to set the distance.

	Note
	When transforming a path, Preview options are not valid: only Outline is active. When you click on the image with the Perpective tool to transform a path, the path disappear from the image but re-appears as soon as you move a handle.

The Information window for perspective transformation

Figure 8.57.  The dialog window of the “Perspective” tool

Matrix

You can get a small knowledge about matrices in the Convolution Matrix plug-in.