Apple Shake 4 - Manual (Page 175)

Chapter 5 Compatible File Formats and Image Resolutions 175
Note: 32-bit unsigned integer channel data will only be useful to custom plug-ins with
built-in logic capable of processing the data within the Z channel.
A major feature of the OpenEXR format is its ability to support an extremely wide
dynamic range. Thanks to its floating-point support, a contrast range of up to 30 f-stops
can be supported with no loss of precision. Color resolution in 16-bit float (“half”) files is
1024 steps per f-stop.
Another advantage of the OpenEXR format is support for any number of additional
auxillary data channels, in addition to the standard RGBAZ channels. For example,
additional channels can be written to store luminance, surface normal direction
channels, velocity channels, and even individual lighting passes written from a 3D
rendering application.
Shake Support for Auxiliary OpenEXR Data Channels
Internally, Shake only supports the processing of RGBAZ channels down the processing
tree. However, the FileIn node provides channel remapping options in the Image tab of
a FileIn node’s parameters. Each channel that Shake supports has a corresponding pop-
up menu. Each menu presents a list of every compatible channel within the referenced
OpenEXR file. Color channels that correspond to Shake’s supported channels are
mapped by default.
To remap any image channel:
1 Load a FileIn node that references an OpenEXR file into the Preferences tab.
2 Choose a new channel to map to from any color channel pop-up menu.
Channel remapping has the following restrictions:
• Any 16-bit or 32-bit float channel can be remapped within the RGBAZ channels.
• 32-bit integer channels can only be remapped to the Z channel.
Note: If you want to access multiple 32-bit integer channels within a script, duplicate
a number of FileIn nodes equal to the number of channels you want to access, then
remap each 32-bit integer channel to a Z channel of one of the duplicate FileIn nodes.
FileIn channel pop-up menus for two files with different image channels