4. Transform Tools
| Chapter 13. Toolbox |

## 4. Transform Tools

### 4.1. Common Features

Figure 13.87. An overview of the transform tools

Inside the Transformation tool dialog, you will find eight tools to modify the presentation of the image or the presentation of an element of the image, selection, layer or path. Each transform tool has an Option dialog and an Information dialog to set parameters.

#### 4.1.1. Tool Options

Figure 13.88. Common options of transform tools

Some options are shared by several transform tools. We will describe them here. More specific options will be described with their tool.

Transform

  GIMP offers you three buttons which let you select which image element the transform tool will work on.

  | Note
  Remember that the Transform option persists when you quit the tool.

  - When you activate the first button the tool works on the active layer. If no selection exists in this layer, the whole layer will be transformed.

  - When you activate the second button the tool works on the selection contour only (the whole layer contour if no selection).

  - When you activate the third button, the tool works on the path only.

Direction

  Direction sets which way or direction a layer is transformed:

  The “Normal (Forward)” mode will transform the image or layer as one might expect. You just use the handles to perform the transformation you want. If you use a grid (see below), the image or layer is transformed according to the shape and position you put the grid into.

  “Corrective (Backward)” inverts the direction. Primarily used with the Rotation tool to repair digital images that have some geometric errors (a horizon not horizontal, a wall not vertical...). See Section 4.5, “Rotate”.

Interpolation

  This drop-down list lets you choose the method and thus the quality of the transformation:

  None

    The color of each pixel is copied from its closest neighboring pixel in the original image. This often results in aliasing (the “stair-step” effect) and a coarse image, but it is the fastest method. Sometimes this method is called “Nearest Neighbor”.

  Linear

    The color of each pixel is computed as the average color of the four closest pixels in the original image. This gives a satisfactory result for most images and is a good compromise between speed and quality. Sometimes this method is called “Bilinear”.

  Cubic

    The color of each pixel is computed as the average color of the eight closest pixels in the original image. This usually gives the best result, but it naturally takes more time. Sometimes this method is called “Bicubic”.

  Sinc (Lanczos3)

    The Lanczos3 method uses the Sinc mathematical function and performs a high quality interpolation.

  You can set the default interpolation method in the Tools Options Preferences dialog.

Clipping

  After transformation, the image can be bigger. This option will clip the transformed image to the original image size.

  You can choose between several ways to clip:

  Adjust

    Figure 13.89. Original image for examples

    Original image

    Rotation applied with “Adjust”

    Rotation applied with “Adjust” and canvas enlarged to layer size

    With Adjust: the layer is enlarged to contain all the rotated layer. The new layer border is visible; the whole layer becomes visible by using the Image → Fit Canvas to Layers command.

  Clip

    Figure 13.90. Example for Clip

    Clip

    With Clip: all what exceeds image limits is deleted.

  Crop to result

    Figure 13.91. Example for Crop to result

    Rotation 45° with Crop to result

    The crop limit is marked with red. No transparent area is included.

    If this option is selected, the image is cropped so that the transparent area, created by the transform operation in corners, will not be included in the resulting image.

  Crop with aspect

    This option works like the one described before, but makes sure, that the aspect ratio is maintained.

Preview

  GIMP lets you select among four Preview possibilities:

  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.

  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 Transform mode.

  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.

  Grid+Image

    Both turn at the same time.

  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.

Opacity

  This slider lets you set the preview opacity.

| Note
When rotating a path, Preview options are not valid: only Outline is active.

3.15. Dodge or Burn |  | 4.2. Move