2017

Custom Color Transforms
Autodesk Color Management lets you create your own .ctf files to define custom color transforms.
Building Custom Transforms
In Smoke, Flame, and Lustre, you can use Custom mode to assemble a chain of transforms, either from the
installed collection or by importing transforms in ASC CDL or third-party LUT formats. You can then export
the whole chain as a single .ctf file for example, to use as a viewing transform or to save time with conversions
that you perform frequently.
Because the .ctf file format can represent arbitrary lists of color processing operations, the exported transform
is a lossless representation of the original processing. In other words, it is much more accurate than baking
the original transforms into a single 3D LUT.
The .ctf file format is XML-based, so you can also use any XML or text editor to create or modify color
transforms. You can either create a transform from scratch, or use <Reference> elements to build a chain
from existing transform files. See
Autodesk CTF File Format Version 1.3 (page 1325).
Dynamic Exposure and Contrast Controls
Some Autodesk applications, like Flame and Smoke, allow you to adjust exposure and contrast interactively
for viewing if those controls have been declared as dynamic in a .ctf file. The exposure and contrast values
set in the application are used for previewing, but the values set in the file are used for processing.
This means that you can create a transform that includes an ExposureContrast operator that does not affect
color values (i.e., exposure of 0 and contrast of 1), and still adjust the exposure and contrast when the
transform is applied to the display. This allows you to check the details in very bright or very dark areas.
However when the same transform is used for processing, the output color values are unaffected.
You can take advantage of this in your own color transforms by referencing one of the exposure-contrast
files in the misc/ directory. There are three versions, so that you can insert them in a scene-linear, logarithmic,
or video color space. The algorithms have been adjusted so that, for example, the exposure-contrast_log
transform causes the exposure and contrast sliders to behave the same in a log color space as
exposure-contrast_linear behaves in a scene-linear color space.
Dynamic Look Controls
Flame and Smoke allow you to toggle a look transform on and off for previewing purposes. The Look On/Off
toggle appears whenever the viewing transform includes one or more operator elements with a LOOK_SWITCH
dynamic parameter. If the same operators have their bypass attribute set to "true", they will be skipped during
processing. This lets you include operators that will never affect values rendered to file but that can still be
toggled on and off for display.
One way to take advantage of this is to define your look transform file as the defaultLook alias. The
defaultLook alias can be set in the LUT preferences, and the setting is stored in the SynColor configuration
file. You can then create a transform chain that includes a reference to one of the transforms in the misc/
directory that in turn references the defaultLook alias:
■ The misc/default_look transform applies the look transform directly.
■ If you are using an ACES workflow and ACESproxy was used on set, you can reference the
misc/default_look-ACESproxy transform instead. This transform first converts from ACES to ACESproxy,
then references the defaultLook transform, and finally converts back to ACES. If your look transform is
an ASC CDL operator and you use the "noClamp" option, then ACES values are not clamped to the
ACESproxy range. Because internal processing is done at 32-bit floating point precision, there will be
negligible quantization loss.
1320 | Chapter 25 Colour Management