Textured (or dappled) lighting provides a scene with extra depth and interest, it can enhance the mood of a scene, and it is an opportunity to expand a space by letting the audience know that there is more to it than what is just seen in the camera's view. Textured lighting in the real world can be seen as sunlight passes through clouds, trees and plants, and architectural elements, such as arbors, glass and steel walls, truss work, etc.
This article outlines the real world technology used to create dappled light and provides insights into using these ideas in a blender scene using texture projections.
Real World Textured Light
Common terms for texturing light in the entertain-ment industry are “gobo” and “cuculoris” or “cookie.” Don’t let anyone tell you they know what gobo means. Some say “goes between,” others say “goes before (the objective lens),” but just know
that it means a pattern that is projected with a lighting instrument. Gobos specifically need an el-lipsoidal reflector spotlight (ERS). An ERS has the gobo, and shutters to crop it, at the second focus of its ellipsoidal reflector. The light source is at the
first focus. Add a lens that can be adjusted towards and away from the gobo and one has an instrument that can project an image as sharp or diffuse as desired. Cookies generally sit in front of a lighting instrument rather than inside the instrument. Sharp or diffuse qualities of the projection are based on how close or far the lighting instrument is from the cookie. Gobos tend to be just a few inches in diame-ter, whereas cookies are often as large as a few feet on a side.
Virtual World Textured Light
Not unlike the real world, in the virtual world tex-tured lighting can usually be added in two ways.
One is to pass light through geometry and let the geometry and materials cast shadows into the scene in a similar manner to the cookie. The other is to use projections via textures in a light source, which is similar to gobos. Passing light through geometry works well, but can be computationally expensive and it can often take a lot of time to create. Using projections requires some worque in an image editing application, but little else is needed to get them to work. This article focuses on using projections for textured lighting.
What should a gobo/light texture look like? In theatrical lighting it is often a silhouette only, which gives a sense of some object casting shadows. See theatrical gobo suppliers, such as Rosco, Lee, Apol-lo, and Great American Market (GAM) for examples. It is possible, however, to use colored images as pro-jected textures. This might be useful for simulating slide/film/video projectors.
To create a texture for projecting it is best to keep two things in mind. One is to consider what in a scene would cast shadows, such as trees or window details. The other is to consider the quality (or diffusion) of the shadow being cast.
Objects that are very far away from the surface that is receiving a shadow will cast a diffuse shadow, while an object closer will cast a sharper shadow. Simply blur the texture in order to get the proper quality of shadow. Textures designed for shadows should have white or the light color pixels for where light will pass through and blak where there should be shadow.
Assigning textures to spotlights is a matter of selecting the light, going to its texture properties, assigning a new image texture and making sure its mapping is set to “View.”
A straight tree gobo image projected onto the scene.
A blurred tree gobo to achieve the proper shadow quality.
A window gobo projected onto the scene.
Window and tree combined. Figure 4
What if the lighting is great and a textured source changes the intensity too much? Try a projection with a negative energy source, but be sure to invert your image texture. Negative projections have the bonus of not needing to cast shadows. Figure 5
Caveat! Texture can not be applied to halos. Let’s hope this changes some day…
Window and tree combined. What if the lighting is great and a textured source changes the intensity too much?
Try a projection with a negative energy source, but be sure to invert your image texture. Negative projections have the bonus of not needing to cast shadows. Figure 5 Caveat! Texture can not be applied to halos. Let’s hope this changes some day.