### 5.5. Lens Distortion

#### 5.5.1. Overview

Figure 17.63. Example for the “Lens Distortion” filter

Original image

Filter applied

This filter lets you simulate but also correct the typical distortion effect introduced in photo images by the glasses contained in the camera lenses.

#### 5.5.2. Activating the Filter

This filter is found in the main menu under Filters → Distorts → Lens Distortion….

#### 5.5.3. Options

Figure 17.64. “Lens Distortion” options

The allowed range of all options is from -100.0 to 100.0.

Presets, “Input Type”, Clipping, Blending Options, Preview, Merge filter, Split view

  | Note
  These options are described in Section 2, “Common Features”.

Main

  The amount of spherical correction to introduce. Positive values make the image convex while negative ones make it concave. The whole effect is similar to wrapping the image inside or outside a sphere.

  Figure 17.65. Example result of Main option

  -100.0

  0.0

  +100.0

Edge

  Specifies the amount of additional spherical correction at image edges.

  Figure 17.66. Example result of Edge option (Main set to 50.0)

  -60.0

  0.0

  +60.0

Zoom

  Specifies the amount of the image enlargement or reduction caused by the hypothetical lens.

  Figure 17.67. Example result of Zoom option

  -100.0

  0.0

  +100.0

Shift X, Shift Y

  These two options specify the shift of the image produced by not perfectly centered pairs of lenses.

  As above this option produces visible results only if the Main or Edge options are non zero.

  Figure 17.68. Example result of Shift X option (Main set to 70.0)

  -100.0

  0.0

  +100.0

Brighten

  The amount of the “vignetting” effect: the brightness decrease/increase due to the lens curvature that produces a different light absorption.

  The Main or Edge options must be non zero for this option to produce noticeable results.

  Figure 17.69. Example result of the Brighten option (Main set to 75.0)

  -25.0

  0.0

  +25.0

Background color

  The part of the active layer outside the lens will have the background color selected here.

  You can select the color:

  - Click on the color button to open the color selector dialog.

  - Click on the eye-drop button on the right to pick a color from the image.

5.4. Engrave |  | 5.6. Kaleidoscope

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