Add a gobo filter to mask a spot light.
- [Narrator] We can now finalize the look of our key light, it's going to represent sunlight coming through a window behind the camera. And we want to achieve the effect of two swathes of light, as if they were coming through two window panes. Just like this window here. This effect is easily done with a Gobo filter and a ramp texture. A Gobo, or cookie, is a cut out shape, placed inside a theatrical, or film lighting instrument to cast shadows onto the set.
Let's select the spotlight, which is the arrow, and go to it's attributes, control A. Open up the Arnold attributes, and scroll down to the bottom, you're looking for light filters. You've got a big field here, which is a list of all light filters that are connected to the current light. And it's empty, because we don't have any yet. We can add a light filter by clicking the add button, or by using this pull-down list. Click on the down facing arrow, and choose AI Gobo, now a Gobo filter has been created, and that node is connected to the current light.
Let's access that Gobo's attributes, at the top of the attribute editor, use the right facing arrow to page through the different node tabs, until you see AI Gobo, and then select that. And here are the Gobo attributes. We don't need to change anything here, except to add a map in the slide map attribute. Click on create render node, and in the create render node dialogue, click ramp. And that of course is a simple gradient.
Let's now test this with a rendering, right click in the camera view to give focus to that view port, without losing the current selection. Go up to the menus and choose Arnold, render. In the Arnold render view, there actually is a Gobo effect in place, but we just don't see it very well. Back in the ramp attributes, set the type to U ramp, and now we can see that the left side is darker than the right side.
I've experimented with this already, and I know the effect that I want, so I'm just going to set that up. The first color swatch here, on the far left, should be white. So swap these out, bring this one over. Not quite all the way to the left, because I want to make some more copies, just click in the center to make another one. And click again to create a third one. So we want one here at a position on zero, and then we want one a little bit further down here.
Let's set that to a value of .415, so it's at position here. .415. And then we want the next one to be black. And we're going to need to make a copy of the black one too, so click in the black area to create a second black one, and then swap these out. So this next black color swatch, or flag, should have a position of .425. And we've got another black one, at a position of .575.
And finally, the last color swatch, or flag, we'll set to a position value of 0.585. And as the Arnold render view progressively renders the shot we can see that, in fact we've got a nice Gobo effect, with just a stripe of black, or shadow down the center. If we wanted to change the softness of that edge, we could change the positions of these color flags, or swatches on the gradient. And that's how to apply a Gobo filter to a spotlight, using a ramp texture.
- Arnold rendering concepts
- Lighting with Maya and Arnold lights
- Controlling exposure
- Filtering light with Gobo
- Light attenuation with Decay
- Image-based lighting with Skydome
- Exterior daylight with Physical Sky
- Arnold Standard Surface material attributes
- Mapping material attributes
- Rendering refractions
- Mesh subdivision and displacement at render time
- Shading effects such as ambient occlusion and vertex color
- Camera effects such as fisheye and depth of field
- Animation image sequence rendering