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Manipulating RPF files in After Effects

Adding Depth of Field and Fog By Stephen Schleicher
In the last installment, I demonstrated how to export an RPF file from LightWave so the files contained Z-depth information that we can use in Adobe After Effects. In this installment, well continue on our final project.

After Effects has had filters for reading RPF data since the 4.1 days, but because many of us may not use a 3D application and a compositing application, we may not have seen much use for them. However with the continued decrease in prices, more and more users are starting to use them for work.

The Production Bundle of After Effects contains five 3D Channel Effects: 3D Channel Extract, Depth Matte, Depth of Field, Fog 3D, and ID Matte. Before jumping into our exercise for this installment, lets briefly look at what each one of these effects do.   The following examples are using characters created by Christophe Desse from www.xtrme3d.com.  These objects are used for demonstration only (and because they look really cool!).

The base RPF image for the following examples (the image is included in the project file at the end of this article).

3D Channel Extract: This effect takes the information contained in the image file and generates a grayscale image that can then be used in a variety of ways (think luma matte or color corrector). This effect allows you to select from a data contained in the image file (these items were selected in the last exercise).

One of the problems with LightWave data in After Effects is that the Z-depth information is relatively shallow. By default the 3D Channel Extract effect has minimum and maximum (black and white points) set at -10000 and 10000. For most of the LightWave scenes I have used, a very small setting (-6 to 6) seems to yield better results.

After manipulating the black and white point settings, a useable matte is created.

In addition to creating a grayscale depth map, you can extract information based on surface normals.

Depth Matte: This effect allows you to create a matte on a layer based on the Z-depth information. This is a very useful effect is you wish to place additional information in the scene, and is what we will use to add the company name to our pill animation.

The Depth Matte Controls are very basic. Depth refers to how far away from the camera the matte will slice the image. Feathering softens the transition, and Invert will invert the depth matte.

NOTE: You should be pretty careful when setting the depth amount. If you use whole numbers only, you may find that some of your objects will get sliced in half! Because of this, you may want to hold down your Control Key to do incremental changes.

Depth of Field: This is probably the effect that most users will use in their work. It does as the name says it creates a depth of field effect causing certain elements in the scene to be in or out of focus.

Depth of Field in action.

The Focal Plane is the point in your scene where your objects are in critical focus. This is often (but not always) a negative number. I found it useful to use the Depth Matte effect to find that region or zone that I want in focus and use that as a starting point. The Focal Plane Thickness determines how deep or shallow your depth of field will be. Maximum Radius determines the fuzziness of the images that are out of focus.

Fog 3D: This effect allows you to fade the scene into a background fog (determined by the color of your choice). For this effect, the Fog End Depth determines where all other objects are completely obscured by the fog (again based on Z-depth). If you want a broken up fog effect, you can use a gradient layer to achieve this.

ID Matte: This effect allows you to matte a layer based on Material or Object IDs. Object IDs are unique number given to different objects in your scene, while the Material ID is based on a surface name. This effect is great if you need to isolate one particular object or color in a composition and make adjustments to it.

In this image, the truck was selected with the Object ID, then the effect was inverted. This leaves all of the other objects in the scene except the truck.

NOTE: When using these effects (especially the matte effects), you may notice a great deal of fringing around the objects. To solve this, you may need to apply the Simple Choker effect with a radius of 1.

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Related Keywords:lightwave, after effects, z-depth, rpf, rla, 3d channel, schleicher


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