User Manual

Lock RGB
When enabled, the settings in this tab affect all color channels equally.
Disable this control to convert the red, green, and blue channels of the image using separate
settings for each channel.
Level
Use this range control to set the black level and white level in the log image before converting.
The left handle adjusts the black level, while the right handle adjusts the white level. Pixels with
values in log space below the black level become out-of-range values below 0.0. Pixels with
values above the white level become out-of-range values above 1.0 after conversion.
When processing in floating-point color space, both negative and high out-of-range values are
preserved. When using 16-bit or 8-bit mode, the out-of-range values are clipped.
Soft Clip (Knee)
The Soft Clip control is used to draw values that are out of range back into the image. This is
done by smoothing the conversion curve at the top and bottom of the curve, allowing more
values to be represented.
Applying a soft clip of any value other than 1 causes the node to process at 16-bit integer,
eliminating all out-of-range values that do not fit within the soft clip.
Film Stock Gamma, Conversion Gamma, and Conversion Table
These controls are used to set the response curves of the logarithmic data during conversion.
In addition to the settings above, a custom ASCII file Lookup Table (LUT) can be created with
specific conversion values. The ASCII LUT file can be loaded using the Browse button.
Common Controls
Settings Tab
The Settings tab controls are common to all Film nodes, so their descriptions can be found in
“The Common Controls” section at the end of this chapter.
Black Rolloff
Since a mathematical log() operation on a value of zero or lower results in invalid
values, Fusion clips values below 1e-38 (0 followed by 38 zeros) to 0 to ensure correct
results. This is almost never an issue, since values that small have no visual impact on
an image. To see such tiny values, you would have to add three Brightness Contrast
nodes, each with a gain set to 1,000,000. Even then, the values would hover very
close to zero.
We have seen processes where instead of cropping these minimal values, they are
instead scaled. So values between 0.0 and 1e-16 are scaled between 1e-18 and 1e-16.
The idea is to crush the majority of the visual range in a float image into values very
near to zero, then expand them again, forcing a gentle ramp to produce a small ramp in
the extreme black values. Should you find yourself facing a color pipeline using this
process, here is how you can mimic it with the help of a Custom node.
The process involves converting the log image to linear with a very small gamma and a
wider than normal black level to white level (e.g., conversion gamma of 0.6, black of 10,
white of 1010). This crushes most of the image’s range into very small values. This is
followed by a Custom node (described below), and then by a linear to log conversion
that reverses the process but uses a slightly higher black level. The difference between
the black levels defines the falloff range.
Chapter – 90 Film Nodes 2017