Apple Shake 4 - Manual (Page 900)

900 Chapter 29 Optimizing and Troubleshooting Your Scripts
The Unbreakable Rules of Premultiplication
If you don’t read the full explanation of the mathematics of premultiplication in “ About
Premultiplication and Compositing ” on page 421, here are the two rules you must
always follow when creating a composition in Shake:
• Rule Number 1: Always color correct unpremultiplied images. To unpremultiply an
image, use an MDiv node.
• Rule Number 2: Always filter and transform premultiplied images. To premultiply an
image, use an MMult node.
Combine Image and Alpha Channels Prior to Filtering
If you need to mask, rotoscope, key, or otherwise add an alpha channel to an image,
make sure you do it in such a way that the result is premultiplied prior to adding
filtering nodes.
Unwanted Gamma Shifts During FileIn and FileOut
Shake and Final Cut Pro display and process the gamma of QuickTime movies and RGB
image files differently.
Shake makes no automatic changes to the gamma of QuickTime or RGB image files
and sequences. Users must make sure that their monitor is properly calibrated for
their production environment, and that the viewer lookup parameters are set to the
values required for images to display properly in the Shake Viewer. In particular, the
default viewerGamma value is 1, which leaves the gamma of images displayed in the
Viewer unchanged.
Final Cut Pro, on the other hand, makes some assumptions about the gamma of
QuickTime and RGB image files that are imported into a project. The gamma of
imported QuickTime and RBG image files is treated differently in sequences set to
render in 8-bit or 10-bit YUV.
Note: While it is possible to recalibrate Apple displays via the Display Calibrator
Assistant in Displays preferences, users should leave the gamma of their monitors to
the 1.8 Standard Gamma setting when working in Final Cut Pro. ColorSync settings are
not used by either Shake or Final Cut Pro for automatic color calibration or
compensation of any kind.
Gamma in QuickTime Movies
When importing a QuickTime movie created with Shake into Final Cut Pro, users may
notice a difference in the displayed gamma of the image. This is because Final Cut Pro
automatically lowers the gamma of sequences playing in the Canvas on your
computer’s display. The gamma of QuickTime images remains untouched when the
sequence is output to video or rendered as a QuickTime movie.