Monday, July 1, 2013

Modeling Monday 6


A GOBO is something put in front of a light to create light patterns or shadows in the image.  The term comes from theatrical lighting where it stands for Go Between Optics.  The focusing high power stage lights put some limits on GOBOS that we can overcome in 3D Art.

The are made as simple geometric shapes in an image editing program such as GIMP, Photoshop, etc.  Even simple image programs can make GOBOs.

Here are some GOBOs for light patterns.

Create a plane with DAZ Studio's Create menu -> CreatePrimitive...

Name it in the scene tab to easily distinguish from other planes the scene. Then use the GOBO image in the Opacity Strength image (small down pointing arrow then browse to the GOBO image)  The black portion will become invisible and the white portion will block light.  Be sure your GOBO plane has cast shadows on.

Place this GOBO plane behind the camera (so its not visible in the scene ) and in front of a light.  Its possible to get a good idea where the light is going to be my looking through the lights view (in the camera drop out list)

It doesn't work with a distant light because the distant light is everywhere and doesn't have an effective position.

Substitute a spotlight for the distant light ( sun in the 2EZ light setup ).  This light is blocked by portion of the GOBO as expected plus it has the added advantage -- the spread angle controls the width of the light cone which allows keeping it from going around the GOBO.

The results in the image can only be seen correctly in a render, the preview is not entirely accurate for this effect. A good way to tune the effect is with shadow softness the image above is 25%

Once a good GOBO location is set up,  It is easy to try out the library of GOBOs, but just substituting different GOBO images in the Opacity Strength of the GOBO plane.

Lighting GOBOs are usually are exposed to high heat and extreme magnification,  so they are usually cut from sheets of metal, which limits what they can be.  3D scenes don't have these restrictions, so it is possible to use grayscale images for more effects that black and white.

These images can be prepared with contrast changes, etc.

Color is possible, too.  Because Opacity Strength is an absorption model colors are inverted.  To invert a color subtract each of its RGB values from 255.  So if this orange  200 200 0 is wanted use 55 55 255.  The resultant color will be close, but is strongly influence by light color and the color of the surface it strikes.