Lighting plug in

Current version: 0.37 beta (see notes below)
Last changed: 17-Sep-1996
Upcoming changes/bugfixes? Yes
Tested platforms: IRIX 5.3, SunOS 5.4 (Solaris 2.4), SunOS 4.1.3
GIMP API version: 0.54.1 (Tue Feb 13 10:29:00)

The plug-in source code is available [here]

Notes:

• The Sine/Log/Sphere mapping doesn't always do what I want.
• The documentation is not even half-finished.
• There is probably bugs.

Table of contents

Introdution

This plug-in enables you to add various types of lighting effects to your (RGB) image. Optionally you can specify a refractive, reflective layer on top of the image to achive special effects (glass, water, slime, distortion etc.) You can choose among three light models:

• Directional light
• Point light
• Spot light

You can choose to apply lighting on image only, layer only, both or none. Additionally you can specify two kinds of mapping to apply to your image or layer. One is the traditional "wavy" mapping which makes a -uhm- wavy mapping. The other is "bump-mapping", where you specify another image as source for your bumps. Also, for the refractive layer, you can specify seperate mappings for index of refraction and layer thickness (more on this later).

Light position and direction

In this section I will explain how to set the position and direction of the light source, and try to suggest some useful settings. All coordinates are relative to the image mapping, which is the unit square [(0,0)..(1,1)] (upper left, lower right).

Directional light

Directional light is non-local light such as the Sun, i.e. light-sources "infinitely" far away. A few common direction settings; [0.0,0.0,1.0] (light directly from above), [-1.0,-1.0,1.0] (light from above, upper left corner), [1.0,1.0,1.0] (light from above, lower right corner). Well, you get the idea :) The default settings for this light-type is [-0.5,-0.5,-1.0].

Point light

Point light is local light-sources, like a free-hanging light bulb of no size. Positioning it at (0.5,0.5,+Z) places it above the center of the picture. The Z value should be positive, although I have not (yet) restricted you from entering negative values; you could get pretty odd results by doing it, though. Default position is [0.5,0.5,2.0].

Spot light

Spot light is like a, er, well.. spot light :) A directional point light, or something :) In addition to a position (P), you specify a direction (D) and a angle (A), which controls the light fall-off effect. A spot light defines a cone with its apex at P, its principal axis along D, and its range controlled by A.

Usage examples

• Create 3D boxes, free-hand frames and logos
• Box example
• Frame example
• Logo example
• Add glassy effects and distortions to your image
• Water/wave example
• Glass lens example
• Distortion example
• Misc. cool examples.. :)

Main dialog

Refraction settings dialog

Material settings dialog

This dialog lets you adjust the material properties of your image or layer. The values set here are critical for how the result will look, so make sure you experiment a bit with them and understand what they do.

• Two-sided shading - turn two-sided shading on/off. Enabling this will result in high-lights appearing at the "dark-sides" of things too. Cool in some cases. Try it.
• Ambient intensity - this value decides how "dark" your image should be where no light falls. Settings this to 0.0 means black, while 1.0 means that the image doesn't get darker at all. Common settings are 0.2, 0.5 and 0.7.
• Diffuse intensity - this value controls the "darkness" of the lighting of your image. Smaller values means darker image. This values is usually set to 1.0.
• Diffuse reflectivity - controls the amount of light to be (diffusely) reflected from your image. Higher values makes your image reflect a lot of light (appear lighter or more intense), while smaller values makes it appear more dull or matte. Good values should probably be 0.2 through 0.6.
• Specular reflectivity - decides how "intense" the high-lights will appear. A value of 1.0 makes your image very shiny (bright high-lights) while smaller values makes you image less shiny, making the high-lights dimmer. The most common values are 0.2, 0.5, 0.8 and 1.0.
• Highlight - makes the high-lights more or less focused. Higher values result in more intense/focused high-lights, whereas small values makes them more diffuse, or unfocused (less noticable). Note that effect of this value is expotential. The values I most often use are 3.0, 7.0, 10.0, 27.0 and 200.0.

Wave settings dialog

Map from image dialog

From this dialog you can specify from what image you want to map, how to scale the data from the image and how to map the scaled data to fit your needs. Here's an explanation of what the various fields do:

• Map from image - contains a list of images from which you can map the effect (IOR,thickness,bump) you have chosen. Only RGB and grayscale images are allowed. RGB images will be converted to grayscale on the fly.
• MinValue - Map zero values (black pixels) to this value
• MaxValue - Map full values (white pixels) to this value
• Map function - Specifies how to the mapping is to be done. Linear mapping uses the data as it is. Logarithmic takes something like this and turns it into something like this. Sinusoidal transforms it to this. Finally, there's the sphere map.
• Autostretch - stretches the value range of the input image from its minimum and maximum values to zero (black) and full (white) before applying the transfer-mapping (see MinVal/MaxVal). This is somewhat like the "contrast autostretch" applied to gray-scale images.

Dialog screenshots

1. Main dialog
2. Refraction dialog
3. Material dialog
4. Wave dialog
5. Map dialog