Apple Shake 4 Tutorials Manual de usuario descargar pdf (Pagina 175)

Chapter 5 Using Keylight 175

Although this is an extreme color correction used for illustration purposes, the principal

concept here is that you spit out an unpremultiplied image, do your color corrections

or transformations, then composite with preMultiply enabled. You can alternatively use

On Black for your output from Keylight, apply a Color–MDiv, do your color corrections,

then apply a Color–MMult to get the same result, but this complicates the tree.

Testing a Color Correction

The following is a handy trick. Use the viewer lookup table (VLUT2) to gauge the color

correction. If it is a good correction, the foreground blacks should be somewhat similar

to the background blacks when the gamma is boosted, and the brights should be

similar when the gamma is lowered below 1.

To evaluate the color correction:

1 In the Viewer shelf, turn on the VLUT2 button.

2 Right-click the VLUT 2 button, then choose Load Viewer Lookup Controls into

Parameters2 Tab from the shortcut menu.

3 In the Parameters2 tab, adjust the viewerGamma slider from .1 to 4 to evaluate the

correction.

If things look good, turn off the VLUT2 button.

You have now pulled a basic key using Keylight and tested some of its parameters to

adjust the mask. Since the parameters were not sufficient to remove the grain of the

image but keep the hair detail, a garbage mask was created, thereby removing most of

the noise. Afterward, a color correction was applied. You used a viewer lookup table

(VLUT) to test both the key and the color correction.

Advanced Keylight Techniques

This part of the tutorial focuses on more Keylight parameters and also discusses the use

of anamorphic images.

For the following example, use the five foreground and background images (at video

resolution) in the $HOME/nreal/Tutorial_Media/Tutorial_05/images directory.

A Bad Correction Highlights Are Good Lows Are Good

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Apple Shake 4 Tutorials Manual de usuario Pagina 175