9.4. Lighting Effects
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### 9.4. Lighting Effects

#### Overview

This filter is found in Image>Filters/Light Effects/Lighting Effects.

This filter simulates the effect you get when you light up a wall with a spot. It doesn't produce any drop shadows and, of course, doesn't reveal any new details in dark zones.

#### Preview

When Interactive is checked, parameter setting results are interactively displayed in preview without modifying the image until you click on OK button.

If "Interactive" is not checked, changes are displayed in preview only when you click on the Update button. This option is useful with a slow computer.

#### General Options

- Transparent Background: Makes destination image transparent when bumpmap height is zero (height is zero in black areas of the bumpmapped image).

- Create New Image: Creates a new image when applying filter.

- High Quality Preview: For quick CPU...

- Enable Antialiasing: Lowers the scale effect on lines. Depth is the strength of antialiasing. Threshold determines which transitions will be considered as a border. High values will limit the effect to strong transitions.

#### Light

Light Settings

  Light Type: Three types are available. Point displays a blue point at center of preview. You can click and drag it to move light all over the preview. Directional: the blue point is linked to preview center by a line which indicates direction of light. The white light halo has an elliptic shape. None: there is no blue point. Light comes from the top left corner, the best to give a good relief effect.

  Light Source Color: When you click on the color dwell, you bring a dialog up where you can select the light source color.

  Position: Determines the light point position according to three coordinates: X coordinate for horizontal position, Y for vertical position, Z for source distance (the light darkens when distance increases). Values are from -1 to +1.

#### Material

Intensity Levels

  These options don't concern light itself, but light reflected by objects.

  Ambient: Sets the ambient light, i.e the indirect light which lightens all the scene out of the light spot

  Diffuse: When you increase this value, light progressively diffuses to the whole image

Reflectivity

  Diffuse: Higher values make the object reflect more light.

  Specular: Controls how intense will be the highlights.

  Highlights: Higher values make the highlights more focused.

#### Bump Map

Enable Bump Mapping

  Combined with "Environment Map", this option allows interesting bump mapping. Only greyscale images can be used for bumpmaps (light areas are bumped, dark areas remain unchanged). So, if you want to bumpmap against a RGB image, you have to turn it to greyscale first (<Image>Image/Mode/Grayscale). When you check this box, following options are enabled:

  - Bump Map Image: You have to select there the greyscale image.

  - Curve: Four curve types are available: Linear, Logarithmic, Sinusoidal and Spherical. See Bump Map plug-in for explanations.

  - Maximum Height: This is the maximum height of bumps.

  - Minimum Height: This is the minimum height of bumps.

  - Autostretch to fit Value Range: There is correspondence between grey level and height. If difference between black and lightest grey is not enough to fill the height value range determined above, then values are stretched.

#### Environment Map

Enable Environment Mapping

  When you check this box, the following option is enabled:

  - Environment Image: You have to select there a RGB image.

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