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Rusting Away

Blending CG text with the real world By Stephen Schleicher
As a compositing wizard, you may be asked to blend a CG element onto a real world surface. Transfer Modes and Opacity changes will only take you so far before you reach the end of their limit. In this After Effects Production Bundle Tutorial, well take an image and composite it believable on top of a rusted piece of metal.

Open After Effects and create a new composition using the DV/NTSC preset. It doesnt matter how long the comp is since you will be working with still images.

Speaking of images. For this exercise, I created a simple smiley face in Photoshop with an Alpha channel. For the rusted backdrop I downloaded a rust image from the MourgeFile.com (http://www.morguefile.com/). This is a great repository of images that you can use as reference for 3D models, or to use in a project like this weeks exercise.

Import the image files into After Effects and place them in the Timeline, with the Smiley face on the uppermost layer.

To get this effect as believable as possible, the Smiley face needs to not only appear to have faded and worn over time, but also needs to appear distorted by the rough surface. To do this well use a displacement map.

A displacement map works by distorting pixels both horizontally and vertically based on the color values in a second layer, called the displacement map. While any layer will work, you can often get better control if you use a black and white or grayscale image.

Duplicate the rust layer, by pressing Command+D on the Mac or Control+D on the PC.

To get a black and white image to work with, well need to convert the image. With the duplicate layer selected in the Timeline apply the Channel Mixer effect from Effect>Adjust>Channel Mixer.

This effect uses a mix of current color channels to modify a single color channel. You can use this effect if you need to make adjustments that are not easily done with other effects. If you wanted to create a tinted image you can adjust the constant amounts, which specifies the base amount of the input channel (Red, Blue, Green) that should be added to the output channel. In order to create a black and white image, use the Monochrome button.

Since the Rust layer has a heavy dose of red in it, and because that is the portion of the image that is "higher" than the rest, it is best to adjust the red channel information.

In the Effect Controls Panel, change the Red-Red amount to 200 to increase the red amount in the image. To bring out as much red as possible, change the Red-Constant amount to -30, and lower the Green-Green to 0. Blue-Blue can be left at 100 to create more contrast in the image. Finally turn on Monochrome to create the grayscale image.

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Related Keywords:After Effects, rust, displacement map, opacity, schleicher

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